Strength And Conditioning Programme Physical Education Essay

Strength and Conditioning is the combination of resistance training and endurance conditioning that is used by athletes and sports teams to improve and assist their performance (Driskell, 1999). Sport specific fitness can include a structured progressive program that could comprise of power, muscular endurance, strength, speed, aerobic or anaerobic conditioning (Steindler, 1955). It has been shown that strength and conditioning programs increase sports performance, producing better athletic results and reducing the incidence of injury (Burrows, 2007). Strength and conditioning programs are suitable for athletes performing at recreational levels, elite levels, sports teams or anyone else looking to ascertain new training methods that might raise their performance capabilities (Baechle & Earle, 2000).
The aim of this assignment is to undertake a needs analysis for a chosen sport and position and to design and outline a six week training programme suitable for the individual athlete. The assignment will consider periodization as well as an analysis of the macrocycle, mesocycle and microcycle sections of a training programme.
The sport and position that will be discussed within this report is football and a central defender. Football is a demanding sports in terms of the effort the players need to put into the game. Football training and conditioning is essential. Players can cover around 8-12km during a match of which 24% is covered by walking, 36% covered by jogging, 20% coursing, 11% sprinting, 7% moving backwards and 2% moving whilst in possession of the ball (Reilly, 1996).
Central defenders need a wide range of attributes, which include height, Strength, balance and a good mentality. Saif (2002) claimed that a defender needs to have good concentration during games and also require skill attributes such as tackling and heading.
Football players need to have excellent endurance. They require a VO2max that has been reported to range between 55 and 70 ml/kg/min in elite performers (Bangsbo, 1991). The game is played approximately 80-90% of maximum heart rate (Helgerud et al, 2001). The greater a player’s aerobic capacity, the greater the distance they would cover during a typical game (Reilly & Thomas, 1976).
Many factors need to be considered to plan and implement a successful training programme. These factors include periodization, macrocycle, mesocycle and microcycle along with other essential phases. These are all factors that need to be taken into account in order for a successful training programme.
Periodization is a planned execution of particular training phases (Bompa & Haff, 1996). The training during the periodization phase is based on increasing and decreasing the volume of repetitions, time and amount of sets. In addition an increase and decrease in intensity. These measures are implemented when planning a structured training program. An important characteristic of periodization training is the scheduling of a recovery period. The principal attributes of periodization include creativity, tactical preparation and utilization of the recovery (Bompa, 2005).

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Examples of periodization programmes include, Stepwise where training includes high volume with low intensity and progresses to low volume and high intensity. In addition, Undulating periodization is used. This is where volume and intensity of training are changed throughout the course of a short period of time. Periodization is the most effective form of training when aiming to improve on muscle strength, motor performance and body composition.
The macrocycle can be defined by four different components. These components include the number of competitions, dates of competitions, the recovery period between competitions and the preparation period before competition. (Dick, 2002)
The microcycle is the smallest part of the overall program as it accounts for only one week of the training. The mesocycle is the part of the year that the athlete is in, for example ‘mesocycle 1’ will be the pre-season phase. The macrocycle is the overall program based over a year (Dick, 2002).
The Anatomical Adaptation is established at the start of the season or immediately after the transition phase. It is introduced before the season starts as it adapts the body for future strength programs. The aim of this stage is to involve all of the muscle groups which prepare muscle, ligaments, and tendons and joins in preparation for training. These strength programs should look to include all parts of the body such as arms and legs but also for the core area, which includes the lower back, abdomen and spinal column musculature. The muscle areas present support for the arms and legs, to help absorb any shock during exercises that require landing or falling. This period is essential because it generates objective growth of the muscles.
Maximum strength phase sets to develop the highest force possible. The training requires the athlete to train at 85-100 percent of 1RM. Many sports require power, muscular endurance or a mixture of both. This phase will last between 1 and 3 months depending on the athletes needs (Bompa, 2005)
The conversion phase transforms the maximum strength that has been developed ready to use during competitive. This conversion occurs when specific training is performed. Throughout this phase an assured level of maximum strength must be acquired otherwise power will deteriorate. Weight training is the most appropriate method of doing this. The duration of this period depends on the ability being converted. The customary period is between 4 and 5 weeks. Conversion to muscular endurance is 6-8 weeks due to anatomical changes that take longer to transform (Bompa, 2005).
The competition phase consists of work carried out during pre-season and must be maintained to reduce the probability of detraining. If an athlete does not maintain their pre season training then muscle fibres can decrease, power is lost as there is a decrease in motor recruitment and speed which can result in a decrease of power. These decreases can result in poor performance during the season.
A transition period is commonly known as the off-season. The aim of this phase is to remove any fatigue a player has developed. It is a method of replenishing the energy systems by decreasing the volume of exercise. This can also be an effective way of reducing the psychological stresses that the player could experience during training and competition. This relaxation period can allow the player to loosen up and rest. Although this period has benefits it should last no longer than 4-6 weeks as there would be great deterioration of the players training. (Bompa, 2005).
Training programmes can be developed to aid the development of the player.The goal set to achieve in the training program is to try to improve performance levels. This includes fitness and skill levels. To find the improvements of a player the measurements will be recorded through fitness testing as a marker to distinguish if certain component skills are improving or not (Fleck and Kraemer, 2004). When planning a training programme for a particular sport, Specificity must be considered. This associates to how much difference there is between training and performance. This is very important, as training inappropriately could ultimately have a negative effect on performance.
Performance levels are measured through fitness testing. The levels will be assessed prior to the training program and after the training program to see if, there has been any improvement. Alternatively, the program may show signs of a decrease in skill levels because the training program did not work and therefore changes will need to take place to solve the problems immediately (Brooks, 2004).
When designing a strength and conditioning program the experience of the player must be taken into account. This is because it would be easier to improve a player at a lower level such as amateur league or Sunday league than a player who is at professional level (Reynolds, 1982). This is because; to improve a professional player other factors must be taken into account such as the attitude of the payer. If the player’s attitude to improve is good then it will become easier to improve than if the player has a bad attitude towards it however this could also be a factor for amateur players (Magnusen and Rhea, 2009).
Strength and conditioning programs must take into account the time of year such as if it is Pre season or in season etc. Moody (2007) suggests “The 4 Phases of a football strength training program” which includes, off-season, Off-Season/Early Pre-Season, Late Pre-Season and In-season.
During the off season players should look to build functional strength. Football like any sport, places a lot of demand on the body. Most players kick the ball with a predominat foot and using the same motor patterns, some muscles develop more than others. Some joints are also experience more stress than others. The goals of this phase are to prepare the joints, muscles, ligaments and tendons for more intense work in subsequent phases.
With a good foundation to build on after phase one the player is prepared to move into phase 2 which is the off-Season/early pre-season period where they set to build maximal strength. The goal of this phase is to develop the highest force possible. Since power is our overall outcome, it makes sense to develop strength first and then convert it into football specific power. The aim is to complete this phase before the start of the season. That way the latter stages of pre-season training can focus on power and strength endurance training.
Phase three is the late pre-season – muscular power and strength endurance. In this phase of football strength training, goal is to convert your strength gains into soccer-specific power and muscular endurance. Football is one of the few sports demands roughly equal amounts of explosive force and strength endurance. Plyometric training and/or circuit training should replace sessions in the weight room for this phase. It will last roughly 4-6 weeks depending on your schedule.
Phase four is the in-season maintenance which aims to maintain the gains you’ve made during a strenuous pre-season period without over reaching or over training. This is not one big, continuous phase in your soccer strength training routine. Because the competitive season can last up to 9 months, it should be split up so the strength routine is in smaller cycles.
Periodization of a player to perform maximally at competition level is crucial at times. For example, if the England team try to get maximum performance out of a midfielder for a world cup in four years time, they should make use of a young midfielder of 22, who would then be more of a mature player at 26 when the world cup begins. This Periodization is a long-term assessment; but for the amateur player a short-term assessment will be made (Bompa and Carrera, 2005)
The program will focus on training pre-season for the player so that the player is prepared for the new season in our training program. In addition, the competitive status of which the player will be training for is the amateur league so it will be competitive for the player and with in reason.
The strength of the player will need to be improved through free weights, as in a game situation the player will not be supported by any machines. Muscle groups that are a key in the sport are lower body muscles such as the quadriceps and hamstrings. The movements that will be involved with this are a squat position to strengthen quadriceps, hamstrings and calves. This may need to be done through maximum power. Tackles that the player makes needs to be explosive although the athlete also needs to be able to do this through out the 90 minutes. Upper strength also needs to be maintained to be able to keep balance and be strong enough to jostle for the ball and gain possession.
Another key skill component that will be needed is maintaining cardiovascular endurance. This is maintained by running on a regular basis in an environment, which the player would be performing. This is so that the player is aware of the environment and surroundings. Although working in a regular environment can help with the development of the player, the use of treadmills can also be efficient. Kravitz et al (1996) has shown that heart rate levels are higher with the use of treadmills than is an athlete uses a cycle. These findings suggest that the player would work harder when using a treadmill than training outdoors.
To assess an athlete’s performance fitness tests can be introduced to identify strengths and weaknesses. When tests are complete, the player can then assess what skill components they need to improve on and what needs to be maintained.
It is important to decide the most suitable fitness test, which can be used to measure these skill components. After the tests are identified data can be collected so that analysis can be made to see where the weaknesses and strength are obtained. After this analysis decisions can be made as to what exercises are needed to create the training programme.
Before any training can proceed, a medical of the player must be undertaken. This is to make sure they have no illnesses that can harm them during their training (Waehner, 2010)
The facilities in which the player or a team may train in can vary a person’s ability to train. For example, if a player is training their football skills in the rain on outdoor grass, then it can become very difficult to train indoors as the difference in the environment can affect their ability. Although training outdoors in the rain can be off putting. However it can also be an advantage because it replicates playing in a competitive game where the weather conditions vary.
When assessing the individuals performance we need to fitness test them, so by doing this we are going to assess their cardiovascular system. This can be done by the 12-minute cooper test, which is a field test, which measures how far a person can travel in 12 minutes. This will be done prior to the training program and 6 weeks after the programme to see if there are any improvements within 6 weeks. This will be the same with all the fitness tests that are included to measure the skill components.
Next thing we need to asses is muscular power. We can do this by fitness testing one repetition max test. There are a number of exercises we could use to test this fitness component such as handgrip dynamometer and maximum bench press. The exercise we will be using for this is a squat as it improves lower body for tackling and needs explosive power when in a need for short bursts in a game situation.
Before a training programme can be created, the following training principles should be used. The principle is abbreviated to “S.P.O.R.T” which stands for, Specificity, Progression, Overload, Reversibility and Tedious as a way of guiding my training program.
Specificity is the principle of training that states that sports training should be relevant and appropriate to the sport for which the individual is training in order to produce a training effect (Triplett, 2006) The athlete is going to be training over a 6-week period prior to the new football season. It is important to emphasise the cardiovascular system whilst maintaining key component skill factors. Trying to improve Muscular Power is also a key factor so that the player can sharpen up and be more explosive ready for the new season.
The Principle of Progression implies that there is an optimal level of overload that should be achieved, and an optimal period for this overload to occur (Shepard, 2009). For the athlete to progress when training cardiovascular endurance, he will start off at a level that he is comfortable with and is able to perform such as running for a 10-minute period. For the progression, the athlete can add on 30 seconds each time he runs. Therefore, the next time this athlete runs it will be 10 minutes and 30 seconds, then 11 minutes and so on.
To progress when performing muscular power exercises the athlete could add on an extra 2.5kg every session. This is because if the athlete added to much extra weight they could become injured so progress made should be slower. This should only be prepared if and when the athlete feels, it is possible. If the athlete struggles with the weight, it is highly unlikely that the player will be able to lift anything heavier.
The principle of overload states that a greater than normal stress or load on the body is required for training adaptation to take place (Kavanaugh, 2007). To make sure that the athlete does not over load on his training programme we will be organising a programme that includes three training sessions a week for a 6-week period. This can reduce the risk of the player becoming fatigued and unable to train.
The Reversibility Principle dictates that athletes lose the effects of training when they stop working out. Conversely, it also means that detraining effects can be reversed when they resume training (Powers et al, 2006). When a player has started to progress their skill levels, they could become injured. If injury occurs, reversibility is a big factor that can affect progress. If the player trains three times during a week and sticks to the training program then this should not be a problem. It is much harder to get back into the fitness levels that you once were if reversibility sets in. This is in particular a big vulnerability when working with cardiovascular endurance.
Tedium commonly occurs in those who regularly perform monotonous exercise routines. Unlike fatigue, boredom leads to a lack of desire to exercise, rather than an inability to exercise. Boredom is one of the main reasons why people stop exercising and drop out of sport. It can be avoided if the type and location of exercise is varied, if achievable but challenging targets are set, and if exercise is made more fun (Baechle and Earle, 2000). Boredom sets in when the training program becomes the same every week and there are no goals or challenges for the player to try to achieve. If a training program becomes to boring for a player they may become jaded and therefore it will be very difficult for them to stick to the training program and be motivated for future sessions.
When designing a training program it is important to make sure that the coach assesses the situation of the athlete and starts the program at the level the athlete has reached. For example, if an athlete is at a low level of training then the coach must start the program with easier ability exercises.
The emphasis on the first week of the program is to get the athlete ready and motivated to become active. To achieve this, the program will include high intensity training to get the athlete ready and prepared for the new season and the program will start with Cardiovascular Endurance Training. The skill of the player will also need to be tested and this can be performed by the 12 minutes cooper run and finding out how far the player can run over a 12-minute period.
The results are assessed after the test to create a suitable starting time for this player. The player will start running at 10 minutes. This will then be done 3 times in the first week whilst adding 30 seconds on each time.
In addition, muscular power will also be assessed. To perform this test the player will use weight training and perform squats. Adams et al (1992) found that squats exercises enhance power production, which is why we are using squats as the main exercise in producing muscular power. The player will start off at a weight he can lift and add on 2.5k each time. This will overload the progression of muscular power. Low weights with high repetition would increase muscular endurance and high weights with low repetition would increase muscular strength, so we need to try to avoid this and balance the weight distribution evenly to try to increase muscular power.
Firstly we need to fitness test his ability and by doing this we will do a maximum repetition max test on how many this player can squat. One set of ten squats at a high intensity, which would be a high weight so that muscular power can be strengthened.
The following weeks are set for a progression from week one and to maintain football skills and team work the players must attend club training sessions which is held once a week for an hour and a half.
When the player reaches the final week of the programme, he should feel fit and ready to perform at a high level. His skill levels should be higher as well as his attitude and motivation, this then acts as an indicator to show he is ready to compete in a competitive game situation for the new season ahead.
The final cardiovascular training session should consist of a 12 minute cooper run again to find out if the player has improved or not. My prediction would be that the player would run further this time than he did the first time he ran the 12-minute cooper run, if the results show an improvement then the training program has been efficient. The Athlete should also repeat a muscular endurance test. The one repetition max test should be carried out during the last session to see if the player has improved.
In conclusion, Strength and conditioning programmes can be very useful to the progression of an athlete. Whilst other methods of training have been found useful, a well-designed programme has been shown to improve an athlete’s ability greatly (Burrows, 2007). This could be because the athlete knows exactly what is needed from them and exactly when the effort is needed. The structured plan can give a big confidence boost for the athlete therefore, they will be eager to test their ability with the addition of a test to improve their ability for the season ahead. With the programme set up the athletes and coaches, can set targets and the athlete can then work within the programme to reach the goals. With a well-organised and constructive programme, improvements should be found. When improvements are not found, this indicates that the programme was not successful therefore; a revised programme must be made to aid the athlete.
I feel that there would be great improvements in the athlete’s ability because the programme sets out to achieve goals that were set and was specific to what the athlete needed to work on. No ineffective training was performed leaving the athlete training only what was needed to play at a higher level of football that before the programme.
 

Improvement of Cement Concrete Strength Properties by Short/Long Steel Fibre Additives

Project Title:Improvement of cement concrete strength properties by short/long steel fibre additives

Section 1:  Introduction/Rationale:

The development of industrial and architectural structure refers to the new technology which balance between building plan and auxiliary material with effective performance. Concrete is a fundamental component to use in modern-building due to the ability to mold any shape and form in practical terms. Therefore, concrete construction has made rapid progress in the recent years. However, concrete is significantly more brittle but exhibits a poor tensile strength and strain capacity (Mindess, 2019 p.17). A possible solution is using discrete steel fibre to ameliorate the performance of brittle materials (Mansour et al., 2007).

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The idea of using the fibres as materials reinforcement can reduce the concrete permeability and improve crack control ability. Furthermore, the element of steel fibre control opening also propagation micro-crack in early-stage (or plastic stage) until contributed in final strength of concrete (Brandt, 2008, p.3-9), increases the young modulus,  reduce its consequent growth and water bleeding (Bencardino et al. 2008). Furtherore, steel fibres additive makes concrete more cohesive and isotropic, and transforms it from a brittle to a more ductile material (Wafa and Ashour, 1992). However, the beneficial effect on concrete design depend on many components, for instance type of steel fibre, characteristics of fibre and concrete mix design.

Due to the lack of documentation on the behaviour of steel fibre in concrete mix design with tensile and compressive strength, the investigation of this research was conducted to evaluate and compare the mechanical efficiency of short / long steel fiber reinforcement concrete and steel fiber dosage in plain concrete.

 

Section 2: Research Questions:  

 

How much ratio of long and short steel fibre to mix with reinforcement cement that give the optimum volumetric to compressive and tensile strength?

Which type of steel fibre short  produce greater mechanical impact in reinforcement concrete design?

 

Section 3:  Annotated Bibliography :

 

Tadepalli, P.R., Mo, Y.L. and Hsu, T.T., 2013. Mechanical properties of steel fibre concrete. Magazine of Concrete Research, 65(8), pp.462-474.

Tadepalli (2013) examine the relationship between type of fibres, the characteristic of steel fibre bonding and the amount of steel fibre used in reinforcement concrete design that effect on the mechanical propose of concrete, which I am discussing in my review looking at between our the relationship of bonding steel fiber characteristic with mechanical strength. These authors recommend reviewing case histories and the standard to reduce the risk by use of Soulioti et al., 2011 and ASTM standard, 2011. However, the result of this paper can be used in large scale prestressed concrete beam only.

Fraser, L.T., May, R.N. and Bagala, R.D., 2018. Exploring the Properties of Fiber Reinforced Concrete. Worcester Polytechnic Institute

This paper focuses on the toughness of concrete and the additional of different type of reinforcement material such as glass, steel fibre and polymer fibre. The author compared the corrosion testing resistance by using Shores et al., 2017. Concrete durability is the permeability concrete and Fraser et al. found that the polymer-fibre and steel fibre can reduce the void in mortar. This study will use be useful for my research as it presents a detail overview role of steel fibre can diminish void in concrete. Though, they recognised that they were unable to clearly prove their findings of the mixing ratio between steel fibre reinforcement and concrete mix design. Furthermore, the limitation of room temperature and the moisture are attributing the curing time, multiple cracking and producing a yield strength.

Soutsos, M.N., Le, T.T. and Lampropoulos, A.P., 2012. Flexural performance of fibre reinforced concrete made with steel and synthetic fibres. Construction and building materials, 36, pp.704-710.   

This paper focuses on the quantify different in fluctuations toughness of concrete made with fibre and steel of different shape and length by using the same dosage. Moreover, the researcher compares the influence result of steel fibre configuration, dosage, and synthetic fibre on shear bending performance and mechanics properties of fibre concrete performance has been investigated by Jovicˇic, (2009), p,723-30 and Parker et al. (1974).This article assisted me in understanding the relationship between characteristic of steel fibre and the performance of mechanical properties. However, they recognised that they were unable to clearly prove that their findings the minimal required thickness determined for the different steel fibre types even the same dosage

Ragavendra, S., Reddy, I.P. and Dongre, A., Fibre Reinforced Concrete-A Case Study. In Proceedings of the 33rd national Convention of Architectural  Engineers and National Seminar on” Architectural Engineering Aspect for sustainable building envelopes” ArchEn-BuildEn-2017.                                     

It is clear that this paper categorises the fibre matrix interaction, reinforcement mechanism and performance characteristic is advanced. It performance has been already claim by Swamy et al. (2003) and Surendra (1987, p.83-88). Although it did not examine the primary of steel fibre concrete compressive-tensile strength and steel fibre type to use in experiment, which is the focus of my essay.

Shende, A.M., Pande, A.M. and Pathan, M.G., 2012. Experimental study on steel fiber reinforced concrete for M-40 grade. International Refereed Journal of Engineering and Science, 1(1), pp.043-048.                 

Shende et al. (2012) focus on the micro crack in mortal aggregate is responded in plan concrete M-40 and inclusion of fibres in the mixture. This paper shows the advance admixture of concrete design sulphonate naphthalene polymer properties with Hook Tain Steel fibre. The authors suggested a new model that uses Permalatha et al. (2003) which suggest the new ration of mix polymer with steel fibre concrete design. Even though, it did not examine the relationship between of steel fibre and bending load directly, the methodology used by the author might be applied to my own study.

Section 4:  Methodology: 

 

The research approach influence design and provide to consider benefit and limitation of various available to the researcher in any sources and time. In this research are considered use to type of approaches are available, for instance, which gain from test theories while inductive came from theories. This report uses secondary research approach as it aim to formulate the hypothesis and develop the mechanical performance of concrete mix with short/long steel fibre.

There are two method available for data analysis- Qualitative and Quantitive; this project uses the quantitative data collected that gained form the researches, journal or published on the University of Glasgow website or library  and explored the research question as it allow researchers to conduct in-depth exploration of particular mixture of concrete design.

Project scope:    

Regarding the limitation and scope of this research, the study briefly considered the entire production method, but the main focus was on the interrelationship between materials, their properties and how they can be measured, and the structural behaviour /performance.

Research limitation and constraints: mention time and money contraints, resources.

This study has potential limitation. The effect of time constrains and implementation of data collection method which may have be influenced the bias data or inaccuracy data than would have chosen. Furthermore, the lack of previous studies in the research area are too specific and reliability of data would be out of date.

Ethics consideration:

No ethics consideration needed as secondary research. 

Section 5:  Reference List

 

Alsayed, S. H. and Alhozaimy, A. M. (1999), Ductility of Concrete Beams Reinforced with FRP Bars and Steel Fibers, Journal of Composite Materials, Vol. 33, No. 19, pp. 1792–1806.

Altun, F., Haktanir, T. and Ari, K., 2007. Effects of steel fiber addition on mechanical properties of concrete and RC beams. Construction and Building Materials, 21(3), pp.654-661.

Brookes, A.J. and Meijs, M., 2008. Cladding of buildings. 4 th edn. London:Taylor & Francis

Barros, J. and Figueiras, J. (1999), Flexural behavior of SFRC: Testing and modeling, Journal of Materials in Civil Engineering, Vol. 11, No. 4, pp. 331–339.

Burgers, R., Walraven, J., Plizzari, G.A. and Tiberti, G., 2007. Structural behaviour of SFRC tunnel segments during TBM operations. In World Tunnel Congress ITA-AITES (pp. 1461-1467).

Bischoff, P.H., 2003. Tension stiffening and cracking of steel fiber-reinforced concrete. Journal of materials in civil engineering, 15(2), pp.174-182.

Carlswärd, J., 2006. Shrinkage cracking of steel fibre reinforced self compacting concrete overlays: test methods and theoretical modelling: test methods and theoretical modelling (Doctoral dissertation, Luleå tekniska universitet).

Collepardi, M., 1994. Superplasticizers and air entraining agents: state of the art and future needs. Special Publication, 144, pp.399-416.

Dejke, V., 2001. Durability of FRP reinforcement in concrete: literature review and experiments

Di Prisco, M., Plizzari, G. and Vandewalle, L., 2009. Fibre reinforced concrete: new design perspectives. Materials and structures, 42(9), pp.1261-1281

Fall, D., Lundgren, K., Rempling, R. and Gylltoft, K., 2012. Reinforcing tailor-made concrete structures: Alternatives and challenges. Engineering Structures, 44, pp.372-378.

Jovičić, V., Šušteršič, J. and Vukelič, Ž., 2009. The application of fibre reinforced shotcrete as primary support for a tunnel in flysch. Tunnelling and Underground Space Technology, 24(6), pp.723-730.

Parker Jr, F., 1974. Steel Fibrous Concrete for Airport Pavement Applications (No. AEWES-TR-S-74-12). Army Engineering Waterways Experimemt Station Vicksburg Miss

Ragavendra, S., Reddy, I.P. and Dongre, A., Fibre Reinforced Concrete-A Case Study. In Proceedings of the 33rd national Convention of Architectural Engineers and National Seminar on” Architectural Engineering Aspect for sustainable building envelopes” ArchEn-BuildEn-2017.

Song, P.S. and Hwang, S., 2004. Mechanical properties of high-strength steel fiber-reinforced concrete. Construction and Building Materials, 18(9), pp.669-673.

Soutsos, M.N., Le, T.T. and Lampropoulos, A.P., 2012. Flexural performance of fibre reinforced concrete made with steel and synthetic fibres. Construction and building materials, 36, pp.704-710.

Shende, A.M., Pande, A.M. and Pathan, M.G., 2012. Experimental study on steel fiber reinforced concrete for M-40 grade. International Refereed Journal of Engineering and Science, 1(1), pp.043-048.

Tadepalli, P.R., Mo, Y.L. and Hsu, T.T., 2013. Mechanical properties of steel fibre concrete. Magazine of Concrete Research, 65(8), pp.462-474.

Stiffness and Strength Characteristics of Demolition Wastes, Glass and Plastics in Railway Capping Layers

Stiffness and Strength Characteristics of Demolition Wastes, Glass and Plastics in Railway Capping Layers

Abstract

Increased generation of demolition waste has led to their successful implementation in civil engineering projects. Combination of recycled aggregates with supplementary materials can potentially improve the quality of geomaterials when constructing alternative railway capping layers. In this research, two types of demolition wastes, namely Recycled Crushed Aggregates (RCA) and Crushed Brick (CB) were studied in comparison with two Conventional Capping Materials (CCMs), which are currently used for railway track construction. Recycled Glass (RG) and Mixed Recovered Plastic (MRP) were also blended with RCA to assess their performance. All the materials and mixtures were evaluated in terms of both stiffness and strength. A new Repeated Load (RLT) triaxial testing protocol was introduced based on the induced stress in capping layer to determine the materials’ stiffness. A comparison was made between the current resilient modulus prediction models to find a model better fits the results of demolition wastes and mixtures. Multistage triaxial test was also conducted to determine the strength, friction, stiffness and energy absorption capacity of materials. It was found from this research study that RCA, CB and mixtures of RCA with RG and MRP had equivalent or higher stiffness and strength than CCMs and are suitable alternatives for sustainable railway capping layer construction.

Keywords: Demolition waste; Recovered plastic; Railway capping layer; Sustainable subballast; Resilient modulus; Multistage triaxial test

1.    Introduction

The usage of Construction and Demolition (C&D) wastes in civil engineering projects has become popular for the industrial sectors. This is predominantly due to the extensive pressure on natural resources, the increasing generation of C&D materials, their successful implementation in civil engineering projects, high disposal costs of landfilling, and enhancing environmental sustainability (Vieira and Pereira, 2015).

In Australia, the C&D waste generation increased by 20.7% from 2007 to 2017 and formed a significant 30% of the waste stream produced in 2016-17 (Pickin et al., 2018). While the recycling rate increased from 60 to 67%, it is still lower than target recovery rate of 80-90% set by Australian states’ authorities (Pickin et al., 2018). Recycled Concrete Aggregate (RCA) and Crushed Brick (CB) in particular, comprise more than 50% of C&D waste stored annually in Australia (Arulrajah et al., 2013). In addition, 1.1 and 2.5 million tons of glass and plastic waste were produced in Australia in 2017-18 respectively, which is approximately 8% and 18% of total generated municipal solid waste (Pickin et al., 2018). In the last decade, glass and plastic waste had a relatively stable recycling rate of around 57% and 12% in Australia respectively (Pickin et al., 2018). Plastic had the lowest recycling rate in all the key waste materials with almost all the rest of it was stockpiled in landfill (Pickin et al., 2018).

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Extensive research has been conducted on RCA and CB, to determine their performance as road base/subbase layer and it was generally found that they can meet the requirements of pavement base/subbase layers (Vieira and Pereira, 2015). Previous studies also showed that Recycled Glass (RG) and recycled plastic, including LDPE and HDPE can be used reliably as additives in combination with other C&D materials in road construction (Arulrajah et al., 2014; Yaghoubi et al., 2017). Also, considering the importance of capping (also known as subballast) layer in reducing the generated train’s load at the bottom of the ballast layer to a bearable threshold for the top of subgrade (Selig and Waters, 1994), some alternative materials including mixture of coarse aggregates with shredded waste tire rubber (Signes et al., 2015) and blend of coal wash, steel furnace slag and rubber crumb (Indraratna et al., 2018; Qi et al., 2018) have been introduced recently.

Earlier track foundation design methods for determining granular layers thickness do not consider the resilient modulus, Mr, of the granular layers (Li et al., 2016), however, more robust design methods are also introduced by Li and Selig (1998) and Indraratna and Ngo (2018). According to Li et al. (2016) and Indraratna and Ngo (2018), neglecting the different properties of individual layers will often result in inaccurate estimations of induced stresses in the subgrade, which subsequently influence the overall performance of the railway track significantly. Particularly, the most important factors governing track performance and induced stress on the subgrade are the Mr and thickness of ballast and subballast layer (Li and Selig, 1998; Li et al., 2016; Sayeed and Shahin, 2017). Shahu et al. (1999) and Smith et al. (2006) also reported that the Mr of subballast can have a major effect of induced vertical and horizontal stresses at the ballast-subballast interface. Although Repeated Load Triaxial (RLT) testing protocols have been used successfully for determining the Mr of pavement materials (Arulrajah et al., 2013; Gu et al., 2015), no testing method has been introduced to date for determining the resilient response of capping materials under the induced loading of the train.

Sustainable utilization of C&D aggregates in railway track substructure has not been investigated, despite their successful implementation in pavement constructions. Although the conventional aggregates perform satisfactory in capping layer construction, there are limited regulations for designing these layers. In this research, the performance of alternative geomaterials was compared to the behavior of two types of Conventional Capping Materials (CCMs). Moreover, limited studies on the mixtures of C&D materials with additives such as RG and waste plastic are another motivation of this research to introduce alternative capping materials (Mohsenian Hadad Amlashi et al., 2018; Yaghoubi et al., 2017). According to Poulikakos et al. (2017), almost all the studies on aggregates with waste plastic, only focused on one or two individual types or mixtures of plastic, mainly for road or concrete construction. However, separating plastic requires further recycling operations and consequently is energy consuming which ultimately is not financially viable for construction activities. The Mixed Recovered Plastic (MRP) used in this research is the mixture of several types of plastic waste (including PET, HDPE, PVC, LDPE, PP, PS, and Other), with much lower processing costs. There has been limited study on civil engineering application of MRP to date, particularly in capping layer to utilize the energy absorption of MRP.

In this research, the feasibility of using C&D materials including RCA, CB, and blends of RCA/RG and RCA/MRP as alternative capping materials was investigated. Basic geotechnical properties of materials were compared to two CCMs currently being used in track constructions in Australia. In addition to basic geotechnical testing including Los Angeles (LA) aberration test and California Bearing Ratio (CBR), several specialized tests such as an adopted RLT testing protocol for determining the Mr of capping layer materials and multistage triaxial test have been conducted. The resilient and shear response of materials were compared with those of CCMs to evaluate the behavior of potential alternative capping materials.

2.    Experimental Study

2.1. Materials and Methods

In this research, four types of aggregates and two different supplementary materials were studied (Fig. 1). Aggregates with nominal size, dmax, of 20 mm, include Conventional Capping Materials of Victoria (CCM1), Conventional Capping Materials of New South Wales (CCM2), RCA and CB. RG and MRP were also utilized as supplementary materials in mixtures with RCA, having dmax of 4.75 and 9.5 mm, respectively. Traditional capping materials were obtained from two natural quarries of railway construction projects in Victoria and New South Wales, while recycled materials were collected from two recycling facilities in Victoria, Australia. MRP used in this research was the mixture of different types of plastic (including PET, HDPE, PVC, LDPE, PP, PS, and Other) which can neither be separated nor reprocessed into new products (Fig. 1). Sampling for all the materials has been undertaken according to ASTM D75/D75M (2014) to have a representative particle size.

Laboratory tests were also conducted on the mixtures of RCA blended with 10%, 20%, 30% and 40% of RG and 3% and 5% of MRP. RG contents were designated based on the study of Arulrajah et al. (2014) on RCA/RG mixture, while MRP percentages were chosen according to the results of Yaghoubi et al. (2017) on LDPE and HDPE blends with RCA. Mixture portions were calculated using dry weight measurement rather than volume fractions. This is mainly due to the fact that measurement of by weight percentage in both laboratory and field could be more accurate as the materials’ volume is reliant on the specific gravity and may change by temperature and water content (Indraratna et al., 2018; Signes et al., 2015). Previous studies also used by-weight method in adding RG and waste plastic to RCA (Arulrajah et al., 2014; Yaghoubi et al., 2017).

Particle Size Distribution (PSD) test was conducted in accordance with ASTM D6913/D6913M (2017) using the washing method except for MRP which was sieved by dry method. ASTM D2487 (2017) was implemented to classify the materials based on the Unified Soil Classification System (USCS). Particle density and water absorption of all aggregates were determined based on ASTM C127 (2015); ASTM C128 (2015), while the specific gravity of RG and MRP were obtained following ASTM D854 (2014).

Maximum Dry Density (MDD) and Optimum Moisture Content (OMC) of all the aggregates and mixtures were determined using ASTM D698 (2012). Standard Proctor energy was used following ARTC ETC-08-03 (2017) for capping materials. Previous studies have also used standard Proctor energy in preparing samples of capping materials (Indraratna et al., 2019; Suiker et al., 2005).

In order to assess the degradation resistance of aggregates, LA abrasion test was conducted by ASTM C131/C131M (2014) test method. CBR tests were performed following ASTM D1883 (2012), using standard Proctor energy. Samples were submerged for 4 days by application of a 9 kg surcharge load as recommended by MTM L1-CHE-SPE-178 (2018) for capping materials.

RLT tests were conducted to measure the Mr of materials using a proposed testing protocol for capping layers. Multistage triaxial test was also performed at three confining pressures of 10, 40, and 80 kPa based on AS 1289.6.4.1 (2016); DPTI TP184 (2015). For all the samples, ASTM C702/C702M (2018) was practiced carefully using both quartering and splitting method in reducing sample size.

2.2. Adopted RLT testing Protocol

Different protocols of measuring the resilient response of granular pavement materials have been proposed based on the loading condition of pavement base/subbase layer using RLT test (AASHTO T307, 2012; CEN EN 13286-7, 2004; NCHRP 1-28A, 2004).

Stress state envelopes NCHRP 1-28A (2004) and AASHTO T307 (2012) for pavement base/subbase and CEN EN 13286-7 (2004) for Method B (High-stress level) are plotted in Fig. 2. In AASHTO T307 (2012) and CEN EN 13286-7 (2004), the confining pressure, σ3, is kept constant at each stage and deviator stress follows a stress path inclined sharply toward the Mohr-Coulomb failure line till reaching a maximum value of principal Stress Ratio (SR) (Andrei et al., 2004). Thereafter, σ3 is increased and the vertical stress, σ1, is reset to a low level and is increased steeply again. Constantly experiencing low-stress to high-stress levels may result in either extensive deformation of weak materials even in the first stress path or disability of capturing enough data close to the failure line of strong materials. However, NCHRP-1-28A (2004) proposed harmonized loading protocol in which the initial stress combinations farthest from the line of failure are imposed to the sample, followed by more demanding stress paths (Andrei et al., 2004). This procedure enables capturing maximum number of Mr points over a larger stress state domain, comparing to the two other protocols.

The domain of applied confining pressure used in the three protocols is fairly similar and is approximately between 20 to 150 kPa (Fig. 2). Based on the discussions, numerical simulations, field measurements and laboratory investigations of Indraratna et al. (2015); Indraratna et al. (2018); Indraratna et al. (2019); Qi et al. (2018); Rose et al. (2004); Suiker et al. (2005), σ3 of capping materials, particularly in Australia, is as low as 5 kPa especially at the edge of track to a maximum value of 75-80 kPa closer to centerline. This indicates the inefficiency of current pavement RLT testing protocols in capturing the Mr of capping materials at low σ3. Hence, the confinement of the proposed testing regime was limited from 5 to 80 kPa.

Regarding the induced cyclic deviator stress (σd-cyclic) at top and bottom of capping layer, field studies of Indraratna et al. (2010) determined a range of around 30 to 80 kPa for passenger train and 60 to 120 kPa for coal train at Australia. Based on the analytical and numerical investigations, σd-cyclic of capping layer interface with ballast or subgrade was reported to be between 50 to 150 by Adegoke et al. (1979), 70 to 90 by Selig and Waters (1994), 60 to 90 by Li and Selig (1998), 30 to 90 by Shahu et al. (1999), 50 to 150 by Rose et al. (2004), 30 to 60 by Sayeed and Shahin (2017). While different loading condition and individual layer characteristics, such as layer thickness and Mr values were assumed in these studies, the reported range of most of the studies was consistent with the field studies reported by Indraratna et al. (2010) in Australia. Also, concerning laboratory studies, Indraratna et al. (2015) applied cyclic sinusoidal stress of 41 to 166 kPa on the subballast-ballast interface. Qi et al. (2018) used the maximum cyclic axial stress of 16 to 116 kPa (corresponding to the σ3 of 10 to 70 kPa).

Based on the aforementioned in-situ and induced loading condition of capping layers, and the characteristics of current RLT testing protocols, a new RLT testing protocol was adopted using the NCHRP 1-28 A (2004) approach. As presented in Table 1 and Fig. 2, the range of confining pressures and cyclic axial stresses was determined based on the previous studies discussed earlier, considering the in-situ anisotropy of materials (ν = 0.3), emphasizing on field studies in Australia. Unlike NCHRP 1-28A (2004) which uses a constant principal stress ratio in each stress path, SR varies in the newly proposed protocolat different confinement levels. In other words, higher SR was imposed at lower confining pressures, which is a more realistic condition of an element of soil under moving wheel load when considering in-situ anisotropy and thickness of different sections of track. The same methodology was used in CEN EN 13286-7 (2004) and the proposed protocol of Gu et al. (2015).

For RLT test with constant σ3, the resilient modulus is defined as a ratio of the applied repeated deviator stress to the induced recoverable axial strain (AASHTO T307, 2012), which is a measure of material’s stiffness:

Mr=σ1–σ3ε1=σdε1

(1)

where Mr is resilient modulus, σ1 and σ3 are major and minor principal stresses (axial and confining stresses), ɛ1 is the major principal or axial recoverable strain, and σd is deviator stress. Since this parameter is stress dependent (Andrei et al., 2004), many researchers have introduced resilient modulus models in terms of stress state parameters, as presented in Table 2. Some of the models presented in this table were reformulated by changing σ3 to θ (bulk stress) and/or σd to τoct (octahedral shear stress), to capture the sensitivity of the models to input parameters (Andrei et al., 2004).

3.    Results and Discussion

Geotechnical properties of the aggregates and supplementary materials are presented in Table 3 and the results will be discussed in the following sections.

3.1. Geotechnical Properties

Fig. 3 illustrates the PSD of recycled materials in comparison to the requirement of Australian agencies (ARTC ETC-08-03, 2017; MTM L1-CHE-SPE-178, 2018) for capping materials. The PSD of CB, CCM1 and CCM2 is within the specified limit of ARTC ETC-08-03 (2017), while RCA has less fine content in the range of 0.15 mm to 0.075 mm than the lower limit of both specifications. Both CCM1 and CCM2 have more fine contents than the limit of MTM L1-CHE-SPE-178 (2018), whereas the fine content of CB is slightly below the upper limit. Also, none of the supplementary materials (RG and MRP) satisfy the recommended range of both specifications. As presented in Table 3, RCA and CCM1 have similar gravel content (well-graded gravel with sand), while CB and CCM2 have more sand than gravel (well-graded sand with gravel).

Based on Table 3, particle density of both coarse and fine particles of RCA and CB are similar to the CCMs. While specific gravity of RG is similar to the measured value of Arulrajah et al. (2013), that of MRP is higher than the HDPE and LDPE used in Yaghoubi et al. (2017). Also, RCA and CB have higher water absorption than both CCMs.

As presented in Table 3, MDD of both capping materials is more than (2 Mg/m3). MDD of CB is marginally below 2 Mg/m3 and that of RCA is 1.83 Mg/m3. As plotted in Fig. 4, adding RG up to 30% reduces the MDD and increases the OMC of the RCA/RG blends, which is similar to results of Arulrajah et al. (2014). However, by adding 40% RG, the MDD of mixture increases significantly. According to Vallejo (2001), this is due to transition in fabric of the mixture from coarse grain supported matrix to fine grain supported matrix, in which the sand-sized particles of RCA and RG fill the voids between coarse particles and reduce the porosity of mixture. The MDD of RCA/MRP blend also decreases significantly by increasing the MRP content (Fig. 4), which is expected due to the low specific gravity of plastic (Yaghoubi et al., 2017).

An LA abrasion of less than 50 is usually adopted for capping materials (Li et al., 2016; Selig and Waters, 1994). While RCA and CB show higher degradation than CCMs, all the aggregates meet this maximum criterion.

Following the Australian agencies (ARTC ETC-08-03, 2017; MTM L1-CHE-SPE-178, 2018), the CBR value of capping materials should be more than 50%. All the tested aggregates except for RG meet the required limit (Table 3). As presented in Fig. 5, inclusion of both RG and MRP in RCA has resulted in CBR value reduction. Lower strength of RG to the RCA (Arulrajah et al., 2014) and softer surface of plastics (Arulrajah et al., 2017) to the RCA particles can contribute to this trend. The only strength parameter that has been set by Australian agencies to evaluate the feasibility of using any materials in capping layer is CBR value. Hence, 5% MRP can be blended confidently with RCA for capping layer construction while the usage of RG should be limited to 40% (Fig. 5).

3.2. Resilient Response of Materials

In order to better compare the response of conventional capping materials with the alternative recycled products, the obtained Mr of materials has been re-ordered in accordance with the applied confining pressure and maximum applied cyclic stress from the lowest to highest value as presented in Fig. 6.

Fig. 6(a) shows that the Mr of both CCM1 and CCM2 is approximately in the range of 50 to 150 corresponding to the bulk stress of 37.5 to 560 kPa. The Mr of CCM1 is higher than that of the CCM2, from around 3 MPa at the lowest θ to 15 MPa at the last cycle. Limited studies have reported on the measurement of Mr for railway capping materials. Selig and Waters (1994) used a range of 55 to 125 MPa in their analytical calculations. Shahu et al. (1999) assumed a range of 60 to 100 MPa corresponding the induced major principal stress of 82 to 92 kPa at the subballast-ballast interface. Qi et al. (2018) used the same limit in evaluating the Mr of coal wash, steel furnace slag and rubber crumb mixture as an alternative subballast layer. Their cyclic triaxial test results showed that the Mr of coal wash and steel furnace slag blend with zero and 10% rubber crumb is approximately between 35 MPa (θ = 46 kPa) and 140 MPa (θ = 322 kPa). Li et al. (2016) proposed a required range of 55 to 105 MPa for subballast materials. Based on the available data in literature, the Mr range of both CCM1 and CCM2 falls between the required ranges of this layer (Fig. 6(a)).

The Mr of CB was observed to commence from a lower value than CCMs till σ3 of 40 kPa (Fig. 6(a)). Subsequently, this falls between the ranges measured for CCMs. Also, the Mr of CB is in the range of Mr presented by other researchers for capping materials, as discussed earlier. Therefore, CB can be a suitable alternative material to the capping materials, in terms of Mr. Nevertheless, RCA shows higher Mr compared to the other aggregates used in this study (Fig. 6(a)) showing a 1.4 to 1.9 times higher Mr of CCMs and CB. This superior resilient response of RCA can result in lower induced vertical and horizontal stresses and deformations of track substructure (Shahu et al., 1999; Smith et al., 2006).

Superior resilient response of RCA provides the potential for sustainable utilization of alternative recycled capping materials. Based on Fig. 6(b) and (c), inclusion of both RG and MRP has resulted in decreasing the Mr of the RCA/RG and RCA/MRP mixtures, which is expected as the shear strength of both additives is lower than RCA (Fig. 5) and consistent with the previous observations (Arulrajah et al., 2014; Arulrajah et al., 2017; Mohsenian Hadad Amlashi et al., 2018; Yaghoubi et al., 2017). Particle shape and low particle roughness of recycled plastic can contribute to this trend as well (Arulrajah et al., 2017).

Although by increasing the RG percentage the Mr of the RCA/RG mixtures decreases, the Mr of RCA60/RG40 is still higher than that of CCMs (Fig. 6(b)). The Mr of both mixtures of RCA97/MRP3 and RCA95/MRP5 falls between the Mr values of RCA and CCMs. Fig. 6(c) also shows that at the same σ3, some levels of shear softening have occurred for the RCA/MRP mixtures by increasing the σd even for the inclusion of 3% MRP. This can be related to high SR applied to the sample compared to the other protocols discussed earlier. Attia and Abdelrahman (2011) also observed a similar trend for recycled C&D materials that experienced shear softening under a loading condition with relatively high-stress ratio.

3.3. Comparison of Mr Models

Predictions of all the models in Table 2 were compared with the measured Mr, to determine a more robust model which could be used with the newly proposed protocol for capping materials, especially for the blend of RCA/MRP which experienced shear softening. This was done by measuring Se/Sy ratio, which is defined as the ratio of the standard deviation of the errors (Se) to the standard deviation of the measured Mr of sample (Sy) (Andrei et al., 2004). Se/Sy ratio was given higher priority than the well-known determination coefficient, R2, in evaluating the models as this parameter applies only to linear, unbiased models based on its statistical definition (Andrei et al., 2004).

As presented in Table 2, the models have been categorized based on the number of regression coefficients into 4 groups and Se/Sy ratio for all the samples was calculated for the models of each group and presented in Fig. 7. For some models (like Model 3 and 4), changing the set of stress parameters (like from σd to τoct) does not result in different goodness of fitting parameters. However, since the correlation coefficients are different, it was decided to evaluate all the models.

Fig. 7(a) shows that in the 2-parameter models, confining pressure (Model 1) is the best single-variable predictor and can predict more accurately than some of the 2-parameter models such as model 21 and 22 (Fig. 7(b)). Other single-variable models (Model 2, 3, 4, 5, and 6) has Se/Sy more than 0.2, which shows a low level of their accuracy. For RCA/MRP mixture, increasing σd at the same σ3 has an adverse influence on the Mr (shear softening in Fig. 6(c)). Therefore, Model 7, in 2-parameter models, better fits the results than Model 1 since parameter J2 in this model takes into account the effect of stress ratio. Also, using bulk stress as a single predictor (Model 2) will result in inaccuracy for RCA/MRP mixture as this parameter simultaneously accounts for σ3 and σd.

Fig. 7(b) and (c) also illustrate the Se/Sy ratio of 3 and 4-parameter models. Model 11/12 (3-parameter) and 23/24 (4-parameter) have the best goodness of fit (Se/Sy below 0.06) for CB, CCM1, and CCM2 respectively. However, Model 13/14 or 17/18 in 3-parameter models and Model 26/27 in 4-parameter models generally perform better for RCA and its mixtures (RG or MRP).

For the RCA/RG and RCA/MRP mixture, the R2 of Models 13/14 and 17/18 in 3-parameter models are very close. Therefore, unlike the results reported by Andrei et al. (2004) on unbound natural pavement materials, using σ3 and σd instead of θ and τoct can increase the accuracy of the models especially in the RCA/RG and RCA/MRP blends. This is consistent with the results of Attia and Abdelrahman (2011) on recycled C&D materials, where the samples experienced some levels of shear softening. Therefore, in the 5-parameter model (Model 32), only the pair stress parameters of σ3 and σd were considered with special emphasize on recycled C&D materials and their mixtures.

Since Model 32 as a 5-parameter model takes into account the effect of suction (k4), failure of material, and instability of equation (k5), for the most of the samples gives the highest goodness of fitness in comparison to the other models (Fig. 7(c)). Although the Se/Sy ratio of this model in most of the samples is low, it is slightly lower than some of the 3 and 4-parameter models including 13/14 or 17/18 and 26/27 for RCA and its mixtures.

While Model 32 needs many trial and errors to find the best parameters with the highest goodness of the fit, Models 17 and 26 provide a good balance between accuracy, ease of calculation, and computational stability for recycled materials as a sustainable alternative for capping layer construction with the newly proposed RLT testing protocol. Therefore, the regression parameters of these two models for tested samples are presented in Table 4.

3.4. Stress-strain characteristics

Fig. 8(a)-(c) present the results of multistage triaxial test on RCA, CB and CCMs and the mixtures of RCA with supplementary materials. For all the samples, the deviator stress, q, initially rises with accumulation of axial strain, ɛ1, until it reaches the peak strength, qpeak, and in the post-peak zone, the q decreases with increasing ɛ1. This is generally known as strain softening behavior in which the yield surface in stress space contracts with continuous shearing and is a typical characteristic of dense granular materials and a similar trend was observed for capping materials (Indraratna et al., 2019; Suiker et al., 2005).

As plotted in Fig. 8(a), RCA has the highest strength followed by CCM1. CB has an intermediate strength between the two CCMs, and qpeak of CCM2 at each stage is around half of the RCA, which is the lowest recorded strength among all the aggregates and also mixtures. A similar trend was observed in resilient response of the materials and signifies the superior strength of RCA and intermediate behavior of CB in comparison to the CCMs. Also, CB and CCMs mainly show a relatively ductile behavior as compared to that of RCA which can be related to the higher particle breakage and high amount of cohesive fine content.

According to Fig. 8(b) and (c), adding either RG or MRP content leads to the reduction of qpeak of the mixtures, mainly due to the lower shear strength of both materials (especially MRP) compared to that of RCA. Moreover, the axial strain corresponding to the qpeak has increased by inclusion of RG and MRP. While for RCA/RG mixtures, this increase is insignificant especially below 30% RG content, addition of MRP noticeably increases the ductility of the RCA/MRP blends. Similar observations have been reported in Mohsenian Hadad Amlashi et al. (2018) for the crushed limestone and recycled glass blends and unconfined compression strength results of Yaghoubi et al. (2017) on RCA and plastic mixture.

In terms of RCA/RG mixtures (Fig. 8(b)), up to 20% RG reduces the peak strength of RCA to about 20%. The rate of reduction has increased significantly by increasing the RG content and qpeak has decreased to 45% in the RCA60/RG40 mixture. Ultimately, the shear strength of the highest RG inclusion, RCA60/RG40, is within the range of the two tested CCMs. Similarly, both RCA97/MRP3 and RCA95/MRP5 show 25% and 15% more strength than CCM1.

In order to better assess the behavior of the recycled C&D materials and mixtures, the peak friction angle, ϕpeak, Young’s modulus, E, and Energy Absorption Capacity (EAC) of mixtures were calculated and compared with the range of results of two capping materials, as presented in Fig. 9. Based on CBR values, resilient response, and stress-strain behavior, CCM1 has higher strength than CCM2. Hence, the upper and lower range of CCMs plotted in Fig. 9 is related to CCM1 and CCM2, respectively.

Similar to the Indraratna et al. (2019), ϕpeak of the samples was calculated for the second stage of loading (σ3 of 40 kPa) and is presented in Fig. 9(a). The value of ϕpeak reduces approximately linearly with increasing both RG and MRP content. Since the ϕpeak of RCA is about 20% higher than that of CCM1, the ϕpeak of RCA70/RG30 is still higher than the plotted range for conventional materials, while RCA60/RG40 has similar value to CB and falls within the CCMs range. Also, Both RCA97/MRP3 and RCA95/MRP5 has higher friction angle than capping materials (>50°). Similar results were also observed for other confining pressures, which are not presented herein.

The reduction in Young’s modulus (initial tangent modulus at the first stage of loading) of RCA with addition of RG and MRP is plotted in Fig. 9(b). Low stiffness of RG and especially MRP is the main factor contributing to this trend, but, generally, due to the high stiffness of RCA, all its mixtures have relatively higher E than the range of CCMs. According to Indraratna et al. (2019), the reduction in E is corresponding to the increase of sample’s ductility as can be seen in Fig. 8(b) and (c). RCA/MRP mixtures show higher ductility compared to RCA/RG mixtures, which results in their lower stiffness. The E of CB is also about 17% higher than CCM1.

Energy absorption capacity of capping materials can enhance the overall stability of railway track structure, reduce track degradation and maintenance costs (Indraratna et al., 2018). The total energy per unit volume absorbed by soil sample can be calculated based on the area of stress-strain curve (Fig. 8) to a given value of strain (Babu and Vasudevan, 2008):

where U* is EAC, σ and ɛ are deviator stress and axial strain in triaxial test. Generally, it is expected for capping materials to not to experience an axial strain of more than 2% (Indraratna et al., 2018). More axial strain or reaching post-peak regime of this layer may result in extensive deformation of track structure and development of undesirable differential and total settlements (Suiker et al., 2005). Consequently, the area under stress-strain curve of samples up to qpeak or 2% axial strain, whichever reached first, was calculated at each stage of loading. Fig. 9(c) illustrates the average U* of samples, which has a similar trend to the U* at each stage of loading. While increasing RG content increases the ductility of RCA/RG mixture, the reduction in deviator stress outweighs the increase in axial strain and hence the reduction in U*. Based on the general trend line of RCA/RG mixtures, after 30% RG, the EAC of mixture is lower than the range of CCMs. However, inclusion of MRP enhances the energy absorption of the matrix such that even by adding 3% MRP, the U* of RCA increases by 22% which is around 45% higher than CCM2. This is due to the increase in dissipation of energy by plastic particles rather than the frictional resistance of the sample. This substantial increase in energy absorption as well as higher strength and stiffness of RCA/MRP mixtures (Fig. 6(c) and Fig. 8(c)) than CCMs, provide the opportunity of introducing an energy-absorbing capping layer with superior performance to virgin aggregates. CB also shows an EAC in the range of two tested capping materials.

4.    Conclusions

In this research, the feasibility of using recycled C&D materials including RCA, CB, and blends of RCA/RG and RCA/MRP, with up to 40% RG and 3 to 5% MRP as railway capping layer was studied and results compared to two types of CCMs. Stiffness and strength characteristics of materials and mixtures were evaluated based on the proposed RLT loading protocol for capping layers and multistage triaxial tests. The following conclusions can be drawn:

Generally, basic geotechnical properties of RCA and CB including PSD, specific gravity, water absorption and LA were fairly similar to the CCMs and complied with the requirement of Australian standards for capping layer. Also, in terms of CBR value, RCA, CB and mixture of RCA with up to 40% RG and 5% MRP fulfilled the limit recommended by Australian agencies.

Mr and shear strength of materials showed that RCA had approximately two times higher stiffness and strength than CCMs, while Mr and strength of CB were approximately in the range of tested natural capping materials.

Higher stiffness of RCA provided the opportunity for adjusting the sensitivity of the layer to repeated loading by inclusion of supplementary materials such as MRP and RG. Based on the test results, both blends of RCA with up to 40% RG and 5% MRP had higher Mr than the two CCMs.

For the RCA/MRP mixture which experienced some levels of shear softening during RLT testing, resilient modulus models taking into account both σ3 and σd performed better than θ and τoct.

Based on the results of multistage triaxial test, addition of both RG and MRP reduced the peak strength, peak friction and Young’s modulus of RCA/RG and RCA/MRP mixture. However, in the case of up to 30% RG and 5% MRP, their values were generally higher than CCMs. The values of RCA60/RG40 and CB also were either higher or in the range of CCMs results.

RCA blended with up to 20% RG and 5% MRP are a viable replacement for CCMs with superior performance in terms of stiffness and strength. Although addition of RG decreased the energy absorption capacity of RCA/RG mixture, RCA/MRP blends showed a significant enhancement in energy dissipation compared to CCMs. Therefore, higher content of RG up to 40% can be utilized considering the comparatively lower EAC of the final product.

 

Stimulus Strength and Response in Muscle Fibers

A study of stimulus strength and response, muscle length and tension generated, and contraction strength in gastrocnemius muscle of frogs.

Introduction:

 

The amount of tension in muscles changes based on how many muscle fibers are contracting. When stimulus strength is increased beyond maximal level, tension does not continue to increase because all of the muscle fibers in the muscle are contracting (Hill, Wyse, & Anderson, 2018). The resting length of skeletal muscles maximizes the muscle’s contraction when stimulated (Hill at al., 2018).

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The objective of stimulus-response exercise was to determine the relationship between the strength of the stimulus and the response of the muscle. The length-tension relationship exercise was performed to determine the relationship between muscle length and tension generated in the muscle. The objective of the summation and tetanus was to measure the amplitude of contraction produced in a muscle that is stimulated with repeated pulses delivered at progressively higher frequencies. The objective of the pre- and post-loaded weight and contractile strength exercises were to measure the strength of contraction while the muscle was lifting pre-loaded and post-loaded weights.

 

Methods and Materials:

 

Figure 1:  Set-up for weight and work exercises acquired from Animal Muscle -Skeletal Muscle-Weight and Work-SetupIXTA page AM-1-4 used to produce and record contractions from the frog gastrocnemius muscle.

Figure 2: The equipment setup used to induce and record contractions from the frog gastrocnemius muscle related to length and tension of muscle using IXTA data acquisition unit and power supply.

The frogs were placed in an ice bath for ~15 minutes to anesthetize them. The frogs were then pinned down in a dissection tray and their skin was removed from the legs using scissors, forceps, and a scalpel. Steps for frog gastrocnemius were followed from a video titled Frog Dissection on YouTube. Ringer solution was used to moisten the muscle. The femur bone was clamped to the ring stand holder and a fishing hook was used to attach the Achilles tendon to transducer. The stimulating electrodes were positioned against the muscle about partway between the knee and the tendon as illustrated in Figure 2. The FT-302 Force Transducer was calibrated with no weight and 5 grams.

 

Results:

 

Table 1: Amplitude of muscle twitches generated by stimulus pulses of different amplitudes.

Stimulus Amplitude (V)

Twitch Amplitude (g)

0.000

0.000

0.250

0.000

0.500

2.769

0.750

10.288

1.000

12.046

1.250

20.750

1.500

28.257

1.750

49.130

2.000

60.014

2.250

63.854

2.500

63.944

2.750

68.599

3.000

70.347

3.250

73.564

3.500

79.990

3.750

81.064

4.000

80.645

4.250

83.224

4.500

85.355

Figure 3: Amplitude of muscle twitches (g) generated by stimulus pulses of different amplitudes (V).

Table 2: Muscle length and muscle twitch amplitude for the frog gastrocnemius muscle.

Muscle Length (mm)

Twitch Amplitude (g)

34

2.267

36

36.86

38

64.749

39

87.307

40

59.11

41

54.914

42

7.202

43

5.494

Figure 4: Muscle length (mm) and muscle twitch amplitude (g) for the frog gastrocnemius muscle. The active tension segment and passive tension segment are labeled, respectively.

 

Table 3: Amplitude and times of muscle twitches generated by stimulus pulses of different amplitudes.

 

Muscle Twitch

Stimulus Amplitude (V)

Amplitude (g)

Contract Time (msec)

Relax Time (msec)

Latency (msec)

0.000

0

0

0

0

1.000

99.955

95

160

20

2.000

112.588

100

175

25

3.000

121.634

105

195

25

4.000

124.295

105

180

25

5.000

128.733

105

195

25

6.000

128.766

105

215

25

7.000

128.515

105

210

25

 

Table 4: Strength of muscle contractions during mechanical summation and tetanus.

Stimulus Frequency (Hz)

Amplitude 1st Twitch (V)

Maximum Amplitude (V)

Change in Passive Tension (V)

Summation/Tetanus

0.5

124.612

126.05

0

No

1

120.376

122.636

0

No

2

116.017

116.812

0

No

3

111.796

118.150

81.975

Summation

4

108.676

120.282

113.929

Incomplete tetanus

5

108.604

122.611

121.033

Incomplete tetanus

10

139.881

143.591

143.098

Incomplete tetanus

20

145.456

145.456

145.456

Complete tetanus

30

146.079

146.079

146.079

Complete tetanus

 

 

Table 5: Amplitudes and times of contractions from a post-loaded muscle.

Rod displacement: 19 mm; trace deflection: 1,859 mV; conversion factor: 0.01

 

Muscle Twitch

Post-load Weight (g)

Amplitude (mV)

Distance (mm)

Contraction Time (msec)

Relaxion Time (msec)

Latency (msec)

Work (Weight x Distance)

Rate of Contraction (Amplitude /Contraction Time)

10

164

1.64

95

65

35

16.4

1.73

20

154

1.54

80

65

35

30.8

1.93

30

138

1.38

90

65

50

41.4

1.53

40

128

1.28

80

60

50

51.2

1.60

50

114

1.14

65

50

35

57.0

1.75

60

106

1.06

75

45

35

63.6

1.41

70

97

0.97

65

45

45

67.9

1.49

 

Table 6: Amplitudes and times of contractions from a pre-loaded muscle.

Rod displacement: 19 mm; trace deflection: 1,859 mV; conversion factor: 0.01

 

Muscle Twitch

Pre-load Weight (g)

Amplitude (mV)

Distance (mm)

Contraction Time (msec)

Relaxion Time (msec)

Latency (msec)

Work (Weight x Distance)

Rate of Contraction (Amplitude /Contraction Time)

10

215

2.15

90

65

40

21.5

2.39

20

199

1.99

80

60

35

39.8

2.49

30

195

1.95

95

65

30

58.5

2.05

40

192

1.92

80

65

40

76.8

2.40

50

187

1.87

100

55

45

93.5

1.87

60

177

1.77

100

50

35

106.2

1.77

70

164

1.64

90

60

45

114.8

1.82

 

 

Figure 5: Work plotted against load weight, both pre- and post- load.

 

Discussion and Conclusions:

 For the stimulus response exercise, the twitch amplitude increased from 0.500 V stimulus amplitude up to of 3.750 V, and decreased at 4.000 V. This data agrees with the expected results because a small amplitude was produced when a weak stimulus was applied due to the contraction of only some fibers. Additionally, when a strong stimulus was applied, all of the muscle fibers contracted, which caused a large amplitude. At 0.250 V, the twitch amplitude response was 0.000 mV because few channels were open, which was not enough to produce an action potential that reached threshold. The length-tension exercise results were supported by literature. As the muscle length increased to normal resting length for a frog, the overlap of the thick and thin filaments increased optimal cross-bridge binding with actin. Twitch amplitude decreased as length increased past moderate muscle lengths because sarcomeres had less overlap of thick and thin filaments (Hill at al., 2018).

 In the mechanical summation and tetanus exercise, once mechanical summation was present, the change in passive tension increased as stimulus frequency increased until the maximum amplitude and change in passive tension were equal. Tetanus was observed at high stimulus frequencies of 20 and 30 Hz because the reuptake of calcium is very fast. An increase in cytosolic calcium levels activates muscle contraction (Kuo & Ehrlich, 2015). Muscle relaxation is slower after tetanus compared to after a single muscle twitch because there is a larger amount of calcium that needs to go back to the sarcoplasmic reticulum.

Literature Cited:

 

Hill, R. W., Wyse, G. A., Anderson, M. (2018). Animal physiology. Oxford University Press, NY.

Kuo, I. Y., & Ehrlich, B. E. (2015). Signaling in muscle contraction. Cold Spring Harbor perspectives in biology, 7(2), a006023. doi:10.1101/cshperspect.a006023

 

Strength Training for Children and Adolescents

This essay will particular focus on the links between a child development and training load by critically discussing, bone development, muscle mass and strength, menstruation in young females, issues of obesity and physical inactivity, aerobic and anaerobic exercise, and injury. After highlighting the contemporary research surrounding these links, the findings and methodology are evaluated. To begin, a brief definition of training load is put forward. The findings founds within training load and children may not be a as straight forward as it appears as much research has looked at the link between training load and a child’s development, through peered reviewed research. The ways of assessing physical activity training load and development, as well as the reasoning why they should and should not take part in exercise, with reference to bone and muscle changes. Also the implications to menstruation in young female athletes and which exercise type of exercise is better for the young. As well as the negative issues relating to injury during physical activity, with reference to the potential affects in to adulthood. Physical activity and health is also known to be beneficial, however the methods and ways in which this is done may give different results. This will be discussed through how physical activity can improve the quality of life and also how being inactive can have issues. It will be looked at through many health conditions including cardiovascular diseases, hypertension, osteoporosis, cancers, and obesity, and also how physical activity can reduce the chance of getting some of these health conditions.

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It must firstly be mentioned what training load is. Training load is the amount of exercise completed and how much energy used (Rowland, 2005). Children and adolescents have taken part in physical activity through school in physical education classes, but there are those who enjoy exercise more than others. In each case there are physiological implications which can occur, such as developmental issue which can include, bone and muscle problems, injury and health issues such as heart disease, cancers and obesity, as well as menstrual complications in females. Also there are implications for children and adolescents who do not exercise. As children progress into adolescence, the influence of peers and peer pressure becomes noticeable and a widespread decline in physical activity becomes more of a problem. Generally boys will tend to participate in some sort of exercise or sport with friends at a higher intensity than girls (Sallis, 1993). Rowland (2007) suggested that physical activity has many benefits for the young, as it promotes health, thus making you healthy in adult life. However Rowland goes on to mention that more research is needed to look at factors such as frequency and duration of physical activity during childhood as this can determine how reliable the health outcomes maybe in adulthood. Furthermore it was suggested that in the long term that if adolescents are physical active it will enhance bone health and reduce certain cancers such as breast cancer. However Twisk (2001) discussed the onset of many chronic illnesses which start at child and that strategy should be put in to plan to reduce disease early on in life. Exercise found that one important way to stop the on set of disease, but increasing physical during childhood and adolescence. Evidence found that exercise guidelines for children and adolescents is weak, and additional it was found that only a small amount of research which found that exercising when young can be related to health in adulthood. This can suggest that guidelines based on the public, should be more focused on health benefits, rather than how much exercise should be completed on a daily basis.
Behm, Faigenbaum and Klentrou, (2008) produced a review on the recommendations of resistance training on paediatrics, with the correct training methods can be safe and improve health. Studies measuring (anthropometric) children have not found to show an increase in muscular hypertrophy with resistance training in paediatrics with cystic fibrosis and cerebral palsy. Surprisingly it has been mentioned that there is no minimum age to start resistance training in children, however this does need to be structured when exercising. The resistance training in children needs to be with a qualified instruction and while being supervised. This seems in many cases to be unachievable as not every child can have instruction with exercising (e.g. a child running is exercise but does not need instruction or supervision), never the less resistance training exercise can aid in muscle strength, endurance, balance, power and co-ordination and many health benefits. Moderate stress on bones (e.g. weight-bearing exercise) builds a stronger skeleton. Heavy loads or extreme forces can retard bone growth. Therefore, power and heavy weight training should be avoided until later stages of development. Training should be closely monitored during adolescence for signs of stress / overuse. Bones are more susceptible to fractures when growth plates (cartilage sights that are not yet ossified) are still present. If bone growth accelerates faster than muscle length, then undue stress can be placed on the skeleton during growth spurts; this can be exasperated by repetitive exercises or movements. Burrows (2007) found that diseases such as osteoporosis are becoming increasingly high, however weight-bearing exercise is a good way to enhance bone mineral density, making it stronger, if this exercise is continued throughout the growth period. It has been suggested that sport needs to start at perpubertal age to obtain peak bone mass. Sports such as gymnastics and football are recommended to increase peak bone mass. Within this research area there also seems to many authors suggesting that training load will be good for muscle and bone strength, especially weight bearing training as this strengthen the body, additional some authors have mentioned professional support and instruction in training will stop the chances of getting injury, but surely injury will be enviable, as it is the individual who is doing that specific exercise or sport can have an accident.
Despite this there are other issues with training load on the young, especially in females and menstruation, as Eliakim & Beyth, (2003) study found when looking at exercise training, menstrual irregularities and bone development in children and adolescents. Weight bearing exercise has been know to be important in bone development, this is even more important in children and adolescents, as bone mineral density reaches around 90% of its peak by the second decade. Physical activity in childhood and adolescence can reduce the risk on bone disease such as osteoporosis in later life. However strenuous exercise in females can affect there reproductive system causing athletic amenorrhea (this is the stopping of menstruation for six months or more). This is becoming more popular as it is 4-20 times higher than the general populations, especially in the female athlete. This can lead to skeletal fractures, unstable spine and vertebral joints, as well as menstrual abnormalities. As a result female athletes would have to reduce training, to reduce skeletal affects, as this is more harmful to bones growth, especially if a child or adolescence is still at the rapid growth stage at this time and prevent changes in menstruation.
Further issues relating to adolescents and training load are growth, maturation and strength. Bernadette (2006) study looked at whether moderate-high amounts of dance training would influence linear growth and sexual maturation if girl ages 8-11 years old, through puberty. Results found that no change of height velocity of the dancers in year one. However when controlling the groups for maturations, fat mass, lean mass and also extracurricular activities (not dancing), there where found to be no changes in growth or velocity growth in height, sitting height or leg length. Thus finding that there was link between age at menarche and hours and years of dance training. Also resulting in no affect occurring in moderate high level of dance training in linear growth or maturation. However it has been found that preadolescent boys and girls can see meaningful gains in strength with proper training. Although it has been documented that adults and adolescents can achieve significant improvements with strength training, training gains for children have been questioned. The argument that led to the false belief that children couldn’t benefit from training was based on two presumptions. First, it was considered unlikely that notable changes in muscular strength and endurance could occur prior to puberty, due to lower levels of circulating androgens (e.g., testosterone). The underlying assumption was that higher levels of androgens were necessary for improvements in muscle size and strength to occur. Second, children naturally become stronger as they grow, and strength gains beyond that were thought improbable. Previous studies, which seemed to support this, were often limited in study design and research methodology (such as low intensity, low volume or short duration training protocols). Nevertheless, this data seemed to suggest that resistance training was ineffective in the very young population. Faigenbaum (2000)
A growing body of scientific evidence in support of children’s strength training has arisen within the past decade. The literature provides strong documentation that both male and female preadolescents can improve strength significantly with well-designed resistance-training programs. Recent reviews analyze the available research by comparison. Although a relatively small number of studies were included, one review revealed that a majority of studies demonstrated strength gains between 13 and 30 percent as a result of training (Falk & Tenenbaum, 1996). Another reported similar results for children and youth, and each of the studies included in this review indicated that resistance training was generally effective, regardless of participants or study characteristics (Payne, Morrow, Johnson & Dalton, 1997). Gains from strength training for preadolescents are generally attributed to neural adaptations and motor learning, rather than circulating androgens. Muscle hypertrophy, or an increase in the cross-sectional area of a muscle, is not usually detected in children as a result of training. Since muscle size has been correlated with strength, studies indicating no increase in muscle hypertrophy implied that strength training was ineffective in younger participants.
On the opposite side of the scale there are those children and adolescence who do not exercise. It is well known that obesity is one of the biggest health problems across the world, but with children becoming less physical active this will be inevitable, along with several other major diseases which can include coronary heart disease, hypertension, osteoporosis, diabetes mellitus, lung disease and some cancers. Watts, Jones, Davis & Green (2005) study found evidence that non physically active children are most like to become less physically active in adulthood, furthermore it is encouraged that physical activity habits in children help patterns of exercise in adulthood. Random control trails have been designed to look at exercise training in both children and adolescence. The studies found exercise does have beneficial outcomes, but it does always reduce bodyweight, it does however have more beneficial effects to changes in fat and lean body mass, thus showing the need for better assessment in future exercising training studies. Exercise can improve cardiovascular fitness and muscle strength, but little affect on blood lipids and blood pressure in obese youths. Similar important studies have found that exercise improves vascular endothelial function, which was found to be a substitute measure to predict the atherosclerotic risk in children and adolescents who are obese (Celermajer, Sorensen & Gooch, 1992).Training studies have found an improvement in vascular function, however an absence in changes in lipid fractions, haemodynamic variables or glucose metabolism as exercise appears to have a beneficial effect on the vasculature (Watts, Beye & Siafarikas et al, 2004)
Another area which is essential in a children development is the aerobic and anaerobic development in children and adolescence. Cardiovascular function being in childhood but is also different of those of an adult. Children have smaller heart chambers and lower volume than adults, thus finding a lower stroke volume than an adult during rest and exercise. Children have a smaller stroke volume, but a child has a higher maximal heart rate compared to an adult. An adolescent, max heart could be found to be higher than an adult but not quiet as high as a child’s (Sharp, 1995). Although higher heart rates can not be compensated for a child’s lower stroke volume and there’s a child’s cardiac output is lower than in adults (Wilmore & Costill, 1994). Thus suggesting that more of the cardiac output goes to working the muscle in children than it would in adults (Wilmore & Costill, 1994). Children are found to be more naturally aerobic, rather than anaerobic, but unfortunately there are few studies which have found that aerobic capacity in children will improve with training aerobically. Furthermore Rowlands (1992) argued that no study’s have been complied which has the specific outline of 12 weeks training, over three days per week, with heart rates of 160 beats per minute over twenty minutes as a minimum requirement, as well as a large group of participants, with a control, thus being similar to an adults training schedule. Rowland found that if children complete a similar aerobic training routine and intensity to an adult, they would improve there V02 max between 7 and 26%. Which suggests children can improve aerobic fitness from an adult training program. Sharp (1995) found that children have a lower lactate production and the anaerobic threshold in children give heart rates of between 165-170 beat per minute, which is similar to a trained endurance adult. Yet sedentary adult’s anaerobic threshold is between 120-150 beats per minute. Which means that heart rate will be higher in a sedentary child than an adult. More evidence has supported high intensity stimulus theory that activity level in children is not related to V02 max (Rowland, 1992). As children are not as active as they once were, Armstrong & Welsman (1994) stated that they are still aerobically fit, which suggest children are naturally fit. Thus, to improve a child’s natural fitness, a good, strong training program is needed.
Whether children exercise aerobically or anaerobic, there is the issue of heat conditions, also know as thermoregulation. Falk (2008) found that children produce more heat per kilogramme body weight than adults, but their thermoregulatory system is not as good. This is partly because they sweat less. For example, a 12-year-old boy may sweat 400ml per square meter of skin per hour, compared to an adult man’s 800ml. Girls and women sweat proportionately the same, although less in absolute quantity terms. Children also tend to have higher skin temperatures, which hinder the flow of heat from body core to the periphery. However, children have a proportionately greater skin surface area the smaller they are. A young adult weighing 64kg will have a surface area of about 1.80 square meters; an eight year- old weighing 25kg will have a skin area of 0.95 square meters, i.e. 36 per cent more surface area per unit of weight. This helps to correct thermal imbalances, but can be a disadvantage when running in direct sun (or swimming in cold water) – with the possibility of a faster rate of overheating (or overcooling).
Injury is another common occurrence in children who take part in sport and exercise during there development. Adirim (2003) found that within the US around 30 million children take part in sport and exercise, and many of those have an injuries, which is due to overuse, also of those injuries over one third where of school age. With the physical and physiological differences of children and adults, this is one reason why children are more susceptible to injury. Overuse injuries are common, overuse injuries occur from the repetitive application of submaximal stresses to otherwise normal tissues. (Outerbridge & Micheli, 1995) Injuries which are the most common are the ankle and knee. Overtraining and exposure to excessive levels of physical activity can cause an increased chance of injury, overuse injuries can affect normal physical growth and maturation. Prevention is the key, gradual rather than sudden increases in stresses and intensity can usually avoid physical breakdown. Early changes of the training program can ensure successful return to sport.
In conclusion, it can be found after looking through peered reviewed research that training load can have both positive and negative aspects. In research it has found that Moderate stress on bones builds a stronger skeleton. Furthermore heavy loads or extreme forces can retard bone growth. Thus, power and heavy weight training should be avoided until later stages of development. Training load and menstruation in female athletes can have detrimental affects on reproductive development. As a result female athletes would have to reduce training, to reduce skeletal affects, as this is more harmful to bones growth, especially if a child or adolescence is still at the rapid growth stage at this time and prevent changes in menstruation. Surprisingly children are becoming more susceptible to many more health conditions as a result of falling physical activity levels, even when knowing that exercise can improve cardiovascular fitness and muscle strength, but little affect on blood lipids and blood pressure in obese youths. Although it has been found that children are most aerobically fit rather than anaerobic, but unfortunately there are few studies which have found that aerobic capacity in children will improve with training aerobically. Children also have a lower lactate production and the anaerobic threshold in children give heart rates which are similar to a trained endurance adult. Furthermore thermoregulation in children produce more heat than adults, but their thermoregulatory system is not as good. However to correct thermal imbalances, but can be a disadvantage when running in direct sun, with the possibility of a faster rate of overheating or overcooling. Finally injury is another aspect which occurs during a child’s development, when taking part in sport and exercise. The most common injuries are overuse (joints commonly affected are ankle and knee). Children are most susceptible to injury during development as they are not coordinated and react slower than adults. It’s also been found that instructions in training will stop the chances of getting injury.
References

AD Faigenbaum (2000) Strength training for children and adolescents, Clinics in sports medicine, 19(4): 593-619
Sharp NC. (1995) The health of the next generation: health through fitness and sport. Journal of the Royal Society of Health, 115(1):48-55.
Falk, Bareket; Dotan, Raffy, Children’s thermoregulation during exercise in the heat – a revisit (2008) Applied Physiology, Nutrition, and Metabolism, Volume 33, Number 2, 1, pp. 420-427(8)
Outerbridge RA, Micheli LJ. Overuse injuries in the young athlete. Clin Sports Med. 1995;14:503-516
Celermajer DS, Sorensen KE, Gooch VM, et al. Non-invasive detection of endothelial dysfunction in children and adults at risk of atherosclerosis. Lancet 1992; 340: 1111-5
Watts K, Beye P, Siafarikas A, et al. Effects of exercise training on vascular function in obese children. J Pediatrics 2004; 144: 620-5
Falk, B., & G. Tenenbaum (1996) The effectiveness of resistance training in children: A meta-analysis. Sports Medicine 22(3): 176-186.
Payne, V.G., J.R. Morrow, L. Johnson & S.N. Dalton. Resistance training in children and youth: A meta-analysis. Research Quarterly of Exercise and Sport 68

 

Analysis of the Strength Based Model of Healthcare

People with Diagnosis of Mental Health and Disability
Strength based model
Strength based practice is a way to deal with bolster that has an in number concentrate on the recognizable proof of individuals’ capacities, hobbies and abilities and on their qualities and potential. Qualities construct practice is to a great extent established with respect to the work of Charles Rapp from the United States who established the qualities show in connection to case service inside of the psychological well-being division. It is a critical way to deal with directing needs appraisal and service coordination in light of the fact that:
• It is an enabling way to deal with options which have verifiably focus around shortfalls and issues inside of families or individuals requiring backing. In strength construct approach with respect to the qualities and capacities of the individual.
• It maintains a strategic distance from the utilization of defaming, marking or accusing dialect.
• It makes trust inside of individuals and their families by concentrating on what is at present effective or has been fruitful in the past for them.
• It concentrates on individuals’ capacities and versatilities and spots them in the “master” position all alone objectives, aspirations and answers for troublesome circumstances.
• The “expert” support worker is put in the part of accomplice and aide.
• It catches (frequently surprisingly) the constructive things in a man and the individual’s surroundings that can serve as a begin for positive changes.
• Individuals and their families are more occupied with a procedure where they feel they are a critical part, not just a beneficiary of others’ “administration”.
• Groups are seen as an essential wellspring of assets as opposed to obstructions or hindrances to succeed.
Working with a qualities point of view obliges staff to have the capacity to:
• Show duty to the thought that all individuals can learn, develop and roll out positive improvement for themselves and their families.
• Give coherence of bolster and aggregate acknowledgement of the person.
• Concentrate on “what’s solid” not
Strength:
Strength based model helps them to expand the capacity to manage issues and get positive solutions. The strength of strength based models is to help a population of persons with mental sickness to make the move from organized consideration to autonomous living. Strength based model expand the potential in the patient to connect with themselves. The strength builds the capacity and feeling of ampleness inside of the people with disability and mental problems and helps they get the opportunity to acknowledge a best or opportunity in their life. It concentrates on the capable getting on the being by comprehensive an advantage based access to propel the energy in them. It helps the incapacitated people to delegate them in and engages them to do copious for themselves after others offer assistance. It also permits them to plot for themselves and to demonstrate their selves in the society. It empowers to be actualized by the standard of the model which is concentrating on helping the patient to use his or her strength and opportunity and resources as the vehicle for gaining required assets.
Weakness
The weakness is that if there is excessively concentrating on the strength, issues may be avoided. Individuals additionally will be unable to address some new thoughts or roll out improvements if they perform all alone strengths. The strength based model may not be design for individual/families that acknowledge two investigation of handicap and mental health needs with carefully or at top accident agency that could progress to youthful ill-use or dependence. It builds the inactive limits furious into the a priorism of change and not the desires of unique individual. The measure of predominant based arrangement shows the brake which described the proficiency of the people with disarranges to yield an assimilation in the gathering. It can as well prematurely end people that acknowledge double analysis anomalous with unlikely aim.
Assessment:
Strength based assessment in respect to the patients with disability and mental health needs are rely on the individual strength and ability, aspirations, and goals they have inside in. Utilize strength Evaluation which is an instrument to help the patients to investigate in an all holistic, positive way then again strength, resources and aspiration to find out individual disability, to offer assistance access assets in the group that will help with the consummation of recuperation focused goals. The strength evaluation will test into the diverse regions of a man’s life, for example, day by day living, financial, social, profound and recreational topics. It will help to recognize and clear up what is going on at this moment, what has happened in the past with respect to these diverse topics, and how to make a dream for the future. The quality based model was produced to prompt the professionals in a more extensive activity of dependably cartoon on quality. Utilizing the structures concentrated on qualities and shortcomings supports an all encompassing and offset of the qualities and issues of an alone with double investigation of incapacities and mental heath necessities. The qualities access is to be something that totally aides and impacts our persuade it ought to be aphoristic in the accent of connections with the people they serve, the accent of service, aggregation and definitive collaborations, and record other activities.
Planning
The evaluation will help to distinguish particular goals. Utilizing these we will draw up an Individual Arrangement with the individual we are supporting. An Individual with mental health and disability, arrangement helps separate huge objectives into little achievable steps furthermore, to share a few responsibility between the client and support worker. The little steps are the investigation of past, frequently overlooked individual resources is guided for the most part by an examination of nine” life spaces”, which incorporate life abilities, accounts, recreation activity, relationships, life style, occupation/instruction, wellbeing, inner resources ( qualities, confidences, critical thinking), and recuperation. Meanwhile, the case Manager ought to endeavour to hear the client’s goal and desires before they hear proof of his or her past issues, mistakes, or weakness.
Co-ordination
Coordination in the model means a variety of activities composed through general communication with client (mental health and disability) wherever they may be found to guarantee service needs are met. These incorporate, yet are not restricted to, appraisal and assessment, consistent service arranging and observing. The execution of these capacities ought to be organize. Case in point, the caseworker starts an evaluation of the client’s strength, needs and potential answers for the issues. At that point, a care arranges for that addresses the individual’s treatment and other asset needs is produced. That implies the caseworker will help facilitate a complete arrangement of a services and casual support for client.
Prespective
The strength based model is exceptionally realistic for the disabled and mental health needs of a person. Strengthening is a focal topic to this methodology. To engage a person with double issue the assessment must be made and in this manner the achievable objectives will be made alongside the assessment so a very much composed arrangement will be done to accomplish the objectives and the likelihood of the achievement will ideally be high. The patients are helped with restoring a consciousness of internal resources, for example, knowledge, capability and critical thinking capacities ; setting up and arranging lines of operation and correspondence between the patient and outside assets; and supporting with those outer assets keeping in mind the end goal to improve the coherence, accessibility, responsibility and effectiveness of those resources.
Summary of Expected Outcome
The strength evaluation and plan are being used. It gives data to research, supervision what’s more, case load planning goal. The supervisors can look out for the status of individual on their caseload. Those reports likewise demonstrate the measure of work being directed in the different life areas, the recurrence of goal being finished; and the relationship between different patient profiles and their accomplishment in finishing goals.

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The strength based model model results is that the people with double examination of disability and mental health needs is sufficient and proliferating the disability and mental health can aggregate physically fit to the relationship like the usual people after plentiful brainy boundaries. Also, the being may progress decisive favourable circumstances to a top associated and growth some achievement greater than acclimated being however the disabled and mental health can’t be made strides. The people with double investigation of inability and brainy needs can confirmation flourishing rejection casework gave aural the group. The quality based model guidance the alone to go hand in hand with strengthening in their lives. Each alone feels of sufficiency and are arrogant achieved. The advancement and development of imaginative capacities the model empowers people with double examination of disability and mental health to learn. By creating and favourable creative capacities, the quality based growth prototype empowers people with brainy tribulation or dependence on learn, develop, and accumulation certainty. By accumulation candidate capacities of counsel and socialization, this original helps envision of descending into sin of brainy suffering or fixation, expands the proficiency to go hand in hand with the workforce, and keeps up satisfactory predecessors working.
Needs assessment and service coordination
Needs assessment plans are a important part of the NASC procedure. The aim of a comprehensive needs assessment is to evaluate an individual’s current capabilities, resources, aims and necessity. It is also important that the process find out the needs that are most important to the individuals.
The purpose of the assessment process is to evaluate what is essential to increase that client’s ability to taking part as fully as possible in community, whilst considering client’s capabilities, resources, culture, and goal. Also consider client’s family/whānau and support worker, their recreational, social and personal improvement needs; training and education needs; vocational and job requirements. There may be different funding sources for supports within these areas of life, a good assessment is focused on a “whole-of-life” approach and not simply on those areas of a person’s life that are funded by disability support or DHBs.
Assessment
It is a procedure that helps individuals distinguishes their inability support requirement. This includes a needs assessor meeting with a client, more often than not in their home, and fulfilment of a support Needs Evaluation Structure. support Evaluation is important on the off chance that you oblige access administration coordination support and there is a need to get to government supported services.
The goal of the needs evaluation is to make sense of how to augment your independence so you can partake as completely as could reasonably be expected in the society. A Needs Assessor meets with a man (and their support client) to do need evaluation. The fundamental reason for a needs appraisal is to discover what is expected to help a man be as independence as would be prudent in their home and group. The assessor will request data about what the individual can and can’t do what they might want to have the capacity to do, and what help or assets they presently have. The Assessor will likewise get some information about a man’s recreational, social and, education, their preparation and instruction needs, employment needs and where proper, the needs of their family/whanau and support worker.
Planning
After a needs evaluation, an administration organizer meets expectations with the family/whānau to set up a backing plan to meet the organized surveyed needs and goal of the child or youngster and, where fitting, their family/whānau or parental figures. These needs may include: access to a progressive registry on mental health/ community services recognizable proof of current services included in addressing parts of the needs and remaining unmet needs recognizable proof and documentation of activities that are important to address those unmet needs and to accomplish concurred goals at the point when needs can’t be met from openly subsidized services, referrals will be made to a scope of group based services as suitable as per the assessment.
Co-ordination
It is the procedure of selecting and sorting out the service needed to meet the incapacity related needs
that were recognized support assessment. This includes the improvement of a support assessment keeping up or advancing customer freedom. Service Coordination includes educating the client of the choices and make an arrangement for service. This incorporates: assistance of access to group of individual support benefits that will empower individuals with dysfunctional behaviours to lead their lives as independently and gainfully as could reasonably be expected improvement of down to earth services and support choices to address distinguished needs using open, private furthermore, will full ministrations prioritization of the needs of the service client and service of the interest for accessible administrations by deciding relative need between those getting to service improvement of an administration or “way of life” plan the match of accessible asset with necessities, guaranteeing assets are utilized productively service of an assignment for carer help or home based support service, management to support service, including facility services.
Strength
Distinguish the strength of services as underneath:
Advanced cooperation and solid working connections Encouraged a customary survey process service for clients in residential (supported convenience)
Empowered more noteworthy joint working utilizing extra care
Made a solitary purpose of contact
Given a positive ordeal to service to clients and their families
Worked as a feature of the more extensive multi-disciplinary group
There are some its own particular preferences and burdens. The consolidated needs appraisal and service coordination model is thought to furnish a far reaching methodology with a registry of services and alludes and joins the person to those service and alludes and joins the person to those administrations which are chosen. It is proposed that the service which client just needs to manage one individual utilizing this joined model and the NASC pathway is all the more auspicious.
Where the needs evaluation and service coordination capacities are independent , it has been recommended that the preferences are a more engaged needs evaluation regularly embraced by a clinician or a prepared needs assessor , and afterward a more noteworthy extent of service are offered by an service coordinator.
Weakness
The weakness of this model have been proposed as having made additional procedures obliging the needs assessor to hand over the data to the service facilitator. There is the potential for data to be lost. However a few services have proposed that this is a proficient methodology guiding the suitable aptitudes to the parts of the NASC procedure.
Perspective
The Needs assessment and service Co-appointment group helps individuals to get to service that will keep them living securely for whatever length of time that wish. In some DHBs clinicians lead the needs evaluation. While this gives insight about the needs of the person from the clinical viewpoint, it has been recommended that different points of view need to be added to guarantee a comprehensive needs appraisal is attempted. Different DHBs have cured this by asking clinicians to begin the needs assessment with the clinician’s point of view, and afterward including the viewpoints of alternate individuals from the multi-disciplinary group until it is finished.
Extended Outcome
This model discovered potential open doors for service change initiating with a more understanding comprehension of the advantages of a NASC benefit inside of the service continuum and how NASC can be created to improve administration client results. Actualizing the accompanying suggestions will accomplish this. To comprehend and affirm the NASC model that they have picked. This administration model is fortified the upgrade service client responsiveness and enhance coordinating of requirements and desires to administrations. To stretch out NASC obligations to join access service to Group Bolster work and bundles of consideration. This is a developing part of the service continuum. To perceive the estimation of NASC in prioritization of restricted asset and hence put resources into NASC workforce to meet administration necessities. NASC spending plan holding for parts of service, for example, bundles of consideration is further investigated for usage. To audit forms set up to guarantee administration clients needs that may vary over the long haul are tended to. To work collectively to accomplish consistency in frameworks and procedures inside of the locale including embracing gauges, rules, administration particulars, information gathering and evaluation devices. To affirm the favoured ability blend of their NASC groups and try to create NASC aptitude utilizing enrolment strategy, training programme, and developing continuous network.
Comparison between Models
The correlations between (a) strength based models and (b) needs assessment and services coordination, are portrayed as takes after. The strength based model works with disabled with adequate quality to accomplish self-change. In any case, if one experiences extreme incapacities, it will be troublesome to locate an extraordinary quality to complete the activity of the strength based model. Because of the impediment of the disabled, their qualities are not ready to be successfully connected and actualized, not to notice the improvement of them.
The needs assessment model, then again, concentrates on dealing with the goal gathering however does not give them future self-improvements. It intends to give services and backings to incapacitates however not show them how to build up their own specializations.
References
Human Services (2002) A Strength-Based Approach to Working with Youth and Families: A Review of Research retrieved from: http://humanservices.ucdavis.edu/academy/pdf/strength_based.pdf
 

Strength And Conditioning Programs Physical Education Essay

Strength and conditioning programs have been a vital ingredient in the physical developments of athletes for so many years. It is vital and prudent to examine the effects of such strength and conditioning programs in order to examine the changes which of occurred as a result. (Stodden & Galitski, 2010).Testing helps athletes and coaches assess athletic talent and identify physical abilities and areas in need of improvement. In addition, test scores can be used in goal setting. Baseline measurements can be used to establish starting points against achievable goals can be set and testing at regular intervals can track an athlete’s progress in reaching those goals (Baechle & Earle, 2008)

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There are many different variables when conducting strength assessment especially in a team sport setting. For example if strength assessment become too time consuming, coaches are likely to eliminate testing from anything that detracts from the skill related intrusion and practice for competition. Because the development of strength and conditioning is vital for physiological development, improvement in performance and accommodation of the stress of performance to prevent injury, it is imperative that coaches and teachers have a sound protocol on which to base their decision and evaluate their athletes strength capabilities (Horvat et al, 2007).
When examining the literature on strength testing it becomes apparent that there are several different methods and protocols used in the strength testing of athletes. As mentioned there is a variety of ways to determine upper body strength including, Chin ups (Stodden & Galitski), Handgrip dynamometer (Kraemer et al, 2003) and isometric peak torque of elbow (Roemmich & sinning, 1997). There is also a variety of measures used to determine lower extremity strength some of which include, Squat 1RM (Hoffman & Kang, 2003), Half squat (Gorostiaga et al, 2005), Isokinetic peak torque (Roemmich & Sinning, 1997) and isometric peak torque
Mayhew et al (2008) suggested the most feasible way to determine upper body strength, in terms of time efficiency and predictive accuracy is the use of muscular endurance to predict 1RM maximum. However because of the variability that has been shown to be associated with predictive equations the use of actual 1RM testing is used and recommended (Hetzler, 2010). Determining maximal strength to estimate the 1RM by using repetition performed to the point of temporary muscle failure is termed repetition to failure. Using this method a participant selects a load that is believed to be less than his or her 1RM and performs as many consecutive repetitions as possible. The load or repetition to failure score is then applied to any number of available prediction equations to estimate a 1RM value (Mayhew et al, 2008). Although many of these equations are reasonably accurate and precise, most of them do not provide information on the population from which they were developed. This is a concern for the use of these prediction equations because the age, gender and training status of the individuals may affect the accuracy and precision of one rep max estimation (Mayhew et al, 2008).
Strength and conditioning coaches and other practitioners with access to a contrex machine can consider using a isometric muscle strength test as a potential alternative to traditional 1RM testing as it appears to correlate extremely well with the 1RM squat (McGuigan et al, 2010). The Con-Trex MJ isokinetic machine has been recently to the rehabilitation-sports training community. Several scientific studies have used this device to assess static (isometric) and dynamic (eccentric & concentric) function of both the knee extensor and flexor muscles (Maffiuletti et al, 2007). In a study carried out by Maffiuletti et al (2007) the reliability of isokinetic and isometric measurements using the con-trex machine was established, showing it as an accurate measure of isometric strength. Isometric testing has been preferred by some coaches and scientists because it is not confounded by issues of movement velocity and changing joint angle (McGuigan et al, 2010). Also athletes not familiar with a back squat technique may run the risk of injury by incorrect technique which may but extreme loads on the lower back. Isometric maximum voluntary contraction has been shown as a valid and highly reliable measure in vivo force production (test-retest reliability >.94) (Bamman, 1999)
Changes over season
Despite the important contribution of strength and power to the success of a Inter county Hurler, there are no published studies to my knowledge examining the effects of an in season strength and conditioning program on strength performance in Inter-county Hurlers. Strength and conditioning programs have been a vital ingredient in the physical development of athletes for many years. Because the responsibility of strength and conditioning coaches is to assist in the physical development of athletes, it seems prudent to examine the effects of a comprehensive, year-round strength and conditioning program implemented over a number of years. The in-season resistance-training program (RTP) for team sports is a maintenance phase of the athlete’s annual periodized training program, in which the primary focus is on maintaining the strength gains made during the earlier phases of training but research indicates that in season strength training can ultimately lead to improvements in performance variables such as power, strength, and speed. Therefore, designing a training regimen simply to maintain strength and power during the in-season may not be as advantageous for physical performance. However, a delicate balance must be achieved as practice and competition demands place great stress on athletes.
If adaptations in power, strength, and speed are program objectives, a strength coach should be able to determine if their program is producing progressive adaptations in these variables. Perhaps the most appropriate way to determine the efficacy of a strength training program is by incorporating a testing regimen. Longitudinal test data can provide a strength and conditioning coach valuable information regarding their program including (a) assessing an athlete’s ability, (b) identifying athletes’ strengths and weaknesses, (c) identifying potential injury risks, (d) program adherence, and (e) evaluating the strength and conditioning program itself (7). Unfortunately, there are limited published data documenting athletes and adaptations in power, strength, and speed that occur over more than 1 year. The majority of studies that have examined adaptations to resistance training in athletes have been of a short term, generally within 1 year. In each case, resistance training led to improvements in performance measures:
In a study carried out by Gorostiaga et al (2006) the effects of an entire season on physical fitness changes (including strength measure by 1RM bench press) and physical characteristics in elite male handball were measured. The 15 subjects include in the study were assessed four times during a 45 week, 50 game season. The study reported slight but significant increases in the subject’s 1RM bench press at each testing session. These results would suggest through an elite athlete’s competitive season increases and improvement in several physical parameters may be obtained.
In a study carried out by Hoffman & Kang (2003) 53 American college football athletes underwent a variety of physical parameter tests both preseason and post season (12 week later). The physical fitness tests included, speed (40-yd sprint), agility (T-drill), vertical jump height, 1RM bench press and 1RM squat. Looking at the strength test results this study showed strength improvements were seen only in the lower body (1RM squat), whereas strength was maintained in the upper body (1RM bench press). This suggests that strength increases can occur during an in-season resistance training program in American college football players.
In a study carried out by Marques et al (2008) 10 professional volley ball players were monitored over 12 weeks to observe changes in strength and power performance Muscular strength and power were assessed before and after the 12-week training program using 4 repetition maximum bench press and parallel squat tests, an overhead medicine ball throw, as well as unloaded and loaded countermovement jumps. Strength improved by 15% and 11.5% in the bench press and parallel squat, respectively (p , 0.0001). The results show that improvements in upper and lower body strength as well as jumping and throwing are possible during the competitive phase of the training cycle by using a combination of resistance exercises with moderate loads and explosive drills. The changes for upper and lower body performance ranged from 11.8 to 15.0% and 3.8 to 11.5%, respectively.
These studies have provided valuable insight into the influence that resistance training may have on the physical performance measures needed to excel in a given sport such as hurling. However, because of the limited scope of the research, longitudinal tracking was not conducted in these studies. In addition, previous studies may have included different types of training protocols, which suggests a more diligent examination of strength and conditioning programs may be required to monitor the neuromuscular adaptations that occur as a result of long-term progressive resistance training.
It would be interesting to determine if and what magnitude components of physical fitness change during the course of a collegiate hurling season, throughout pre season conditioning, in season competition and post season recuperation. This is important because the primary goal of preseason conditioning is to optimise performance during in season competition (Astorino et al, 2004)
(Stodden & Galitski, 2010)
 

Topology Optimisation for Fracture Strength and Fatigure Life Improvement of Aerospace Structures Design

Significance:

The presence of damage at arbitrary locations in a structure is common in aerospace components [1]. Material flaw as minor as a small surface crack can lead to fatigue failure is one of the most important failure modes in the engineering field [2], being responsible for more than 80% of all structural failures. Topology optimisation has become an effective tool for efficient light-weight design in aviation industry where design approach that treats fatigue life as design objectives is now a standard practice [3]. Fatigue life based optimum design plays a crucial role in restoring the operability of deteriorating structures and altering local structural shapes to extend their operational life beyond expectation [4]. Optimised components,   such as smart structures design of wing ribs, also showed significant weight reduction and improved safety factor [5]. Thus, development and application of optimisation system will be beneficial to existing product development methods such as conceptual and preliminary design process as it reduces manpower, time and cost of implementation [6].

Literature review

Classical optimisation methods, such as density filtering, were originally introduced since when the methodology for topology was well developed and utilised on a regular basis in industrial settings where demands for aircraft structural stiffness were high [7]. The aim of density-based topology optimisation is to find an optimal material distribution which can effectively minimise the structural compliance subject to an overall mass constraint. Such approach is both easy to implement and computationally efficient as explained in [8]. Nevertheless, major design alterations are usually required for stiffness optimal designs to meet requirements of more common design driving criteria such as stress or fatigue as mentioned in [9]. Therefore, it can be useful to introduce stress or fatigue criteria in the formulation of topology optimisation.

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 Although stiffness is not an unimportant property, the key property of a structure is often its durability. This is closely related to the stresses in the structure, and it is common engineering practice to keep the stresses in a structure below its suitable material limit [10]. Despite of its relevance in aviation industry, topology optimisation with stress constraints comes with limitations regarding singularity and computational cost due to large number of constraints [11]. Solutions to such problems; for instance, global stress measure and clustering technique, have been discussed in many papers, see [2], [3], [12]. However, the local stress control is lost and the optimisation problem becomes increasingly non-linear, resulting in impairment of structural integrity [13]. 

While stress-based topology optimisation is an old field of research, investigation in fatigue-based topology optimisation is still a relatively recent and unexplored area in aerospace structures design [14]. As reviewed in [15], this can be justified by the fact that computational cost of Finite Element Method used in analysis is high as iterations of detailed simulation have to be done for each fine mesh. Still, successful practical applications within aerospace industry are evident. For example, utilisation of topology optimisation in the design of the Airbus A380 leading edge ribs and forward strut of aircraft’s nose landing gear [16] both showed considerable decrease in weight and prolongation of fatigue life.

To date, topology optimization has proven to be the most useful, yet most complicated, structural optimization methodology [3]. However, only a few applications to real-world design problems in the aerospace industry are evident. This accounts for the difficulties in design process to ensure that the finalised design complies with the regulations and meet the airworthiness standards in aviation field [17]. Technical hardships due to the fast evolution of aerospace structural engineering have restricted the application of topology optimization from being widely used in the industry [18].

 

References

[1] R. Das and R. Jones, “Damage tolerance based design optimisation of a fuel flow vent hole in an aircraft structure,” Structural and Multidisciplinary Optimization, vol. 38, no. 3, pp. 245-265, 2009.

[2] O. Sigmund, “On the usefulness of non-gradient approaches in topology optimization,” Structural and Multidisciplinary Optimization, vol. 43, no. 5, pp. 589-596, 2011.

[3] J. H. Zhu, W. H. Zhang, and L. Xia, “Topology Optimization in Aircraft and Aerospace Structures Design,” Archives of Computational Methods in Engineering, vol. 23, no. 4, pp. 595-622, 2016.

[4] R. Das and R. Jones, “Development of a 3D Biological method for fatigue life based optimisation and its application to structural shape design,” International Journal of Fatigue, vol. 31, no. 2, pp. 309-321, 2009/02/01/ 2009.

[5] M. Seabra et al., “Selective laser melting (SLM) and topology optimization for lighter aerospace componentes,” in Procedia Structural Integrity, 2016, vol. 1, pp. 289-296.

[6] J. Oest, Structural Optimization with Fatigue Constraints, (Structural Optimization with Fatigue Constraints): Aalborg Universitetsforlag, 2017.

[7] S. B. Dilgen, C. B. Dilgen, D. R. Fuhrman, O. Sigmund, and B. S. Lazarov, “Density based topology optimization of turbulent flow heat transfer systems,” Structural and Multidisciplinary Optimization, vol. 57, no. 5, pp. 1905-1918, 2018/05/01 2018.

[8] U. Schramm and M. Zhou, “Recent developments in the commercial implementation of topology optimization,” in Solid Mechanics and its Applications vol. 137, ed, 2006, pp. 239-248.

[9] E. Holmberg, “Topology optimization considering stress, fatigue and load uncertainties,” 2016. 

[10] M. Bruggi, “On an alternative approach to stress constraints relaxation in topology optimization,” Structural and Multidisciplinary Optimization, vol. 36, no. 2, pp. 125-141, 2008.

[11] E. Holmberg, B. Torstenfelt, and A. Klarbring, “Stress constrained topology optimization,” Structural and Multidisciplinary Optimization, vol. 48, no. 1, pp. 33-47, 2013.

[12] J. Oest and E. Lund, “Topology optimization with finite-life fatigue constraints,” Structural and Multidisciplinary Optimization, vol. 56, no. 5, pp. 1045-1059, 2017/11/01 2017.

[13] E. Holmberg, “Stress and fatigue constrained topology optimization,” 2013. 

[14] Z. Kang, P. Liu, and M. Li, “Topology optimization considering fracture mechanics behaviors at specified locations,” Structural and Multidisciplinary Optimization, vol. 55, no. 5, pp. 1847-1864, 2017.

[15] J. W. Lee, G. H. Yoon, and S. H. Jeong, “Topology optimization considering fatigue life in the frequency domain,” Computers and Mathematics with Applications, vol. 70, no. 8, pp. 1852-1877, 2015.

[16] M. K. Leader, T. W. Chin, and G. Kennedy, “High Resolution Topology Optimization of Aerospace Structures with Stress and Frequency Constraints,” in 2018 Multidisciplinary Analysis and Optimization Conference,(AIAA AVIATION Forum: American Institute of Aeronautics and Astronautics, 2018.

[17] H. Svärd, “Topology Optimization of Fatigue-Constrained Structures,” Doctoral thesis, comprehensive summary, KTH Royal Institute of Technology, Stockholm, 2015:04, 2015. Accessed on: 2015-04-08t22:30:59.713+02:00. [Online]. Available: http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-163575Available: DiVA

[18] D. J. Munk, D. J. Auld, G. P. Steven, and G. A. Vio, “On the benefits of applying topology optimization to structural design of aircraft components,” Structural and Multidisciplinary Optimization, vol. 60, no. 3, pp. 1245-1266, 2019.

 Oest, J 2017, Structural Optimization with Fatigue Constraints. Ph.d.-serien for Det Ingeniør- og Naturvidenskabelige Fakultet, Aalborg Universitet, Aalborg Universitetsforlag.

 
 

Effect of Simultaneous Exposure to Corrosion and Fatigue on Bond Strength Between CFRP and Steel Plates

EXPOSURE TO CORROSION ND FATIGUE ON BOND STRENGTH BETWEEN CFRP AND STEEL PLATES

 

5.1 INTRODUCTION

Corrosion is a serious problem in civil infrastructures, which can significantly jeopardize the structural integrity of the element.  Damaged caused by corrosion can dramatically be exaggerated when combined with an existence mechanical loading (1).

Last few decades many studies carried out on repairing and retrofitting civil infrastructures using the advanced composite materials (1) (2) (3) (4) (5) (6). It has been shown that fiber-reinforced polymer (FRP) composite materials has had a dramatic impact on civil engineering techniques. Adhesively-bonded composites material has led to improve both structural integrity and sustainability performance of these structures. Thorough theoretical and practical studies have been adopted on CFRP to repair steel structures [4, 7, 10, 11, 13, 14, 19, 20-29]. Bond durability has been a focal concerned issue for many researcher [4, 7, 10. 11] due to its effect on the resultant panel. However, studies in this area performed so far have been limited and many issues lack clarification. For example, most studies have studied the behaviour of the bond durability when it has been affecting by either the environment or the loading, however, in most cases that these two factors are existing together in the same time.

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As such, and due to the lack of knowledge in studying the effect of the simultaneous effect of corrosion and fatigue on the steel repaired with CFRP. This chapter presents an experimental study into the combined effect of both a severe environment and mechanical loading (static or fatigue) on the steel repaired with CFRP. The attacking of a severe environment represented by 3.5 % NaCl stimulated sea water at 60 0C, which next will generate the required corrosion. However, these circumstances have to be accompanied with the mechanical loading (static or fatigue). As this is important since steel structures are widely used in conditions where the effect of both environment and mechanical loading are existing. In order to meet these requirements, an experimental design has been accomplished, a description of the experimental set-up and the methodologies that were developed to determine the simultaneous effect of corrosion and fatigue on CFRP/steel repairs is given in Section 5.2. Section 5.3 describes an experiment test that was performed to determine the diffusivity rate of normal modulus CFRP laminates. An experimental investigation into the bond durability of CFRP repairs to steel plates under the combined exposure of corrosion and fatigue is presented in Section 5.4. Section 5.5 presents the results of an experimental investigation performed to evaluate the CFRP/steel bond quality prior to testing. Finally, Section 5.6 discusses new finding made in section 5.4 that aspects of the classical lap joint theory (that underpin the recommendations given in the PABST program and presented in the US Composite Materials Handbook CMH-17-3G [1, 2] are invalid.

5.2 Set Up and Experimental Design

The test design developed to investigate the combined effect of the environment and the mechanical loading on bonded CFRP steel joints is shown in Figure 1. This design lay out, which is given in [3], provides exposure to the corrosive environment while the specimen undergoes mechanical loading, see Figure 5.1(a). Some changes have accomplished to the design in [3] with respect to the specimen size and the steel mechanical properties. This set up briefly consists of two corrosion chambers that are firmly connected with the machine and hold the specimen inside. The main chamber, which was made of acrylic, performs two crucial jobs. One is holding the solution prepared for this test program which is 3.5 % NaCl artificial sea water at a maximum temperature of 60 0C. This chamber also contains a metal grip which penetrates through its bottom and connects the specimen to the lower grip of the fatigue machine. This chamber was not covered at the top as this allows the specimen to be directly connected to the upper grip of the machine. It also has two apertures, upper and lower apertures used for solution inlet and outlet respectively.

Circulation of the inner solution which is inside the chamber was continuously needed to maintain the temperature as same as the solution in the water path as indicated in Figure 5.1(d), to this end a heater and a pump were used to circulate the water and control its temperature inside the chamber. An additional chamber, which was made of metal, embraced the main chamber. The role of this “second” chamber, which is labelled number 7 in Figure 5.1(b), was to guarantee no solution leakage and to support the whole rig inside the upper and lower machine grips.

 

Figure 5.1: Experimental design for the simultaneous effect of environment and     load: a) A schematic view of the design set-up [3], b) experimental set-up of the durability test c) a view of the secondary chamber of the rig, and d) the water bath which contains water pump and heater.

In order to enable fatigue testing to be performed in a normal way, while the specimen is immersed totally in the environment, an additional grip was used to handle the specimen from one end and to connect it to the fatigue machine from the other. The grip that was submerged completely in the environment was made of stainless steel so as to resist the anticipated corrosion, see Figure 5.1(c). The test specimens were designed to fit inside the rig and as such were designed to be a maximum of 400 cm long. The specimens also had a hole at one end in order to be gripped inside the chamber. Thus the bearing capacity of this member was a critical design consideration.

5.3The Moisture Uptake Investigation for Normal Modulus CFRP Plates (Diffusivity Rate)

Prior to onset of the bond durability experiment program, a crucial consideration should be taken into account. The double lab joints specimen configuration has two outer surfaces of CFRP, see Figure 5.2. Hence when this specimen is exposed to the environment (the moisture) during testing, it is important to establish if the moisture has reached the interface between the composite and the adhesive [4].  Consequently, the time required for the moisture to reach the interfaces in-between the composites/adhesive and the adhesive/steel will be determined in this section. To this end, a diffusivity rate experiment of CFRP materials was performed in order to (approximately) estimate the time required for the moisture to be absorbed by the composite and reach the composites/adhesive interface.

 

 

                  Figure 2: Configuration of double lab joint specimen (not to scale)

This was determined as per the standard test, as detailed in ASTM D5229. To this end, 10 CFRP plates specimens of the dimensions (50 x 200 x 1.2 mm) were prepared as shown in Figure 5.3. The dimensions were chosen to be the same as CFRP plates in Section 5.2.

                           

 

Figure 5.3: Normal modulus CFRP plates

Two different exposure temperatures, viz, 20 and 50 0C, were utilised. The weight measurements were done at various time intervals every 24 hour for the first week and every 2 days for the next 12 days. This was done by removing the specimen from the water tank, and extra water on the surface was dried using clean tissues. The change in weight as a percentage was plotted against the square root of time (√t), where t is the time in days. By assuming that the diffusion occurs in one dimension, and ignoring the thickness effect, such as the case represented by a thin film of a thickness adsorbing a fluid according to Fick’s law with constant surface boundary conditions, the amount of diffusant, M2, taken up by the sheet in a time, t, is given by [5, 23], Once the moisture uptake become constant then this is the time that the sea water requires to penetrate the CFRP plate and reach the interface in between the composite and the adhesive, see Figure 5.5. Accordingly, by using equation (1), the diffusivity rate of normal modulus CFRP material has been calculated.

        
D=π+h4M2+M2–M1t2–t12+1+hl+hw–2  ______________________        (1)

Here h, l, and w are thickness, length, and width of the panel, M1 and M2 are the equilibrium sorption attained theoretically at time t1 and t2, respectively. It was found that the times required for normal modulus CFRP laminate immersed in 50 0C and 20 0C to reach their maximum moisture weight gains were approximately 10 to 13 days and 15 to 17 days respectively. This is shown in Figure 5.5, which shows the theoretical moisture uptake behaviour predicted using Fick’s second law of diffusion [6, 7]. Subsequently, the coefficients of diffusivity were 2.52 x10-9 and 3.00 x 10-9 for 20, 50 0C respectively see Table 5.1.

These specimens were first dried in an oven for 24 hours and weighed using a digital balance with precision to 0.01g as shown in Figure 5.4 (a) and (b) respectively. They were then immersed in the environment which was 3.5% NaCl simulated sea water see Figure 5.4 (c) and (d).

Figure 5.4 Steps indicating moisture uptake test, a) Drying step in an oven, b) specimen weighing, c) specimen in sea water, d) specimen in the environment (20 and 50 0C 3.5% NaCl)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 5.5 Moisture uptake curve for the CFRP laminates immersed in sea-water

Table 5.1: Characteristics of moisture uptake and the diffusivity coefficient of normal modulus CFRP laminate at 20 and 500C 3.5%wt NaCl .

The Environment

   Temperature

(0C)

  Maximum moisture

          Uptake (%)

Coefficient of Diffusion      (mm2/s) x 10-9

3.5 %wt NaCl

20

           1.03

                 2.52

3.5 %wt NaCl

50

            1.7

                 3.00

 

 

 

 

 

 

 

 

5.4 The Bond Durability Experiment

5.4.1 Test Configuration and Material Properties

CFRP/steel double overlap fatigue specimens (dofs) with dimensions shown in Figure 5.6 were fabricated. These specimens consisted of two 350 grade mild steel inner adherends bonded to normal modulus (E = 200 GPa) CFRP outer adherends. The dimensions of the steel inner adherents were: 180 mm long, 50 mm width and 5 smm thick. The size and configuration of specimens were designed according to AS1391 specifications (2001) and designed to fit in the designed rig and be tested under fatigue load.

The two outer adherends were a layer of CFRP composite, MBRACE laminate normal modulus (E = 210,000 MPa), 200mm long, 50 mm wide and 1.4 thick see Figure 5.7(b). A CFRP laminate was used since it is perhaps the most commonly used composite material used in the repair of steel infrastructure.

 

Figure 5.6 Schematic design of the CFRP/steel double lap joint.

 

 

 

 

                     Figure 5.7: Material photos (a) Mixed structural adhesive (b) CFRP laminate.

The adhesive used in this test was the epoxy resin adhesive (Araldite 420 A/B) see Figure 5.6(a). Araldite 420 has widespread applications in bonding various structural substances such as metal, wood, rubber, composites and many plastics. This is attributed to its typical properties, namely, design flexibility, extremely tough but resilient, relative rigidity, and its cost-effective characteristic, in addition to it’s room temperature curing property [4] The manufacturer outlines that the CFRP laminate has a tensile strength and an elastic modulus of 3,300 MPa and 210 GPa respectively. A Poisson’s ratio ν12 of the laminate was assumed to be 0.35, which is a typical value for this type of adhesive [8, 11].

5.4.2 Specimens Preparation

The dofs specimen geometry was originally proposed in [9] since it closely simulates the stress state in both the repair and the adhesive associated with a composite repair to a cracked metal structure.

As recommended in [10] surface sandblasting was used as a mechanical surface preparation technique to roughen steel surface. Surface roughness helps to increase the surface area, which enhances adsorption and interlocking, thereby facilitating adhesion and bonding. The steel surface was abrasively sandblasted by subjecting it to an accelerating media (16-grit sand) through a blasting nozzle by means of compressed air. (Note that the gun should be held away about 5 cm from the surface at 450 angles). The (roughened) steel surface was then cleaned first by compressed air to remove the dust sand particles and secondly with acetone using a clean brush. Roughening the surface (sandblasting) and then wiping it with chemical solvent (acetone) can produce a contamination free surface, chemically active and fresh surface, and an interface resistant to hydration due to solvent [4,7,8,11]

A layer of Araldite A/B adhesive was applied to the steel. The patches were subsequently applied, and the surfaces were then rolled using a plastic roller to remove the air bubbles and the extra adhesive. This was done to obtain an even and thin layer of epoxy which comes of two parts A & B, as they should be mixed before using, according to the recommended percentage of 10-4 respectively. The specimen was subsequently left for curing at room temperature for at least 15 days.

5.4.3 Specimens Exposed Process

1. Control Specimens

After curing, 18 specimens were used to determine the ultimate strength of the bond. These specimens were static tested at three temperatures (20, 40, 50 0C) and were taken as control specimens. Nine of these specimens were immersed in sea water at the three temperatures (20, 40, 50 0C) for two weeks prior to tensile testing. This was done with regard to the moisture uptake equilibrium of normal modulus CFRP laminate as calculated in Section 5.3. The remaining nine specimens were tested without pre-immersion.

All specimens were strained, in a 3.5 % (by weight) NaCl solution (i.e., artificial seawater), at a rate of 2 mm/min. To allow for the possible scatter, three (control) specimens were tested at each of the three exposure temperature.

Two dummy specimens with 4 attached thermocouples were used to control the temperature inside the chamber, see Figure 5.8. Before starting the test, specimens were soaked at the required temperature for 25-30 min, to ensure that the entire specimen attained the required temperature. The specimen is then placed in the chamber and submerged in the environment, and then loaded at a rate of 2 mm/min.

 

 

 

Figure 5.8:  Dummy specimens with attached thermocouples determine the temperature of the specimens inside the chamber

 

2. Fatigued Specimens

An additional set of 18 specimens was fatigue loaded under constant cycles, up to a maximum load of 20 % of the specimen’s ultimate strength which (that was independently determined). Nine of these specimens had been pre-exposed at the three different temperatures (20, 40, 50 0C), while the other nine were directly tested under fatigue load (i.e., without pre-exposure). Under each condition, triplicate tests were performed, in order to estimate the scatter in the data. Fatigue testing was performed using an MTS Instron machine with load cell capacity of 100 kN. All tests were performed at a frequency of 10 Hz and a stress ratio of 0.1. The tests were terminated after 2 million cycles and the specimens then subjected to static load until failure. This was done in order to determine the effect of fatigue load on the ultimate strength of the bond. The results of these tests are shown in Table 2.

5.4.4 Results and Discussion

The average ultimate tensile strengths for the specimens and the coefficients of variation with and without pre-exposure to the environment for two weeks are shown in Table 5.2. Here we see that the failure load decreased as temperature increased. On the other hand, pre-exposure procedure has no significant effect on the failure load see Figure 5.9. Figure 5.10 shows that the specimens exhibited both cohesive and adhesive failure at all temperatures [7, 11, 22]. Unfortunately, this means that the surface preparation was inappropriate. This study led to the realisation that alternative surface preparations were needed.

Table 5.2 Average ultimate loads (Fult) and coefficient of variation of CFRP laminate repaired steel plates at different temperatures with and without pre-exposure to environment

Temperature (oC)

Average value of Ultimate loads Fult (kN)

Coefficient of variation

Ultimate strength (kN) (Fave) without pre-exposure

20

40

50

89

56

44

0.01

0.05

0.07

Ultimate strength (kN) after immersion for 2 weeks (Fave)

20

30

50

78

50

40

0.02

0.06

0.07

 

 

 

 

 

 

 

 

 

               Figure 5.9 Static strength of CFRP laminate/steel bonded specimens

Figure 10 Optical images of control specimens after failure, a) with pre-exposure b) without pre-exposure to environment

Bai (2013) [10] reported the effect of varying temperature on tensile strength, whereas, Borrie (2015) [11] tested samples after pre-exposure to environment at different temperatures. In the present study, tests were conducted under the simultaneous effect of environment, load, and with and without pre-exposure. The dimensions and the materials were chosen to be the same as those in [10, 11] for the purpose of comparing the results. Among the various test conditions, simultaneous exposure of pre-exposure samples to environment at an elevate temperature conditions the most severe condition that deteriorates the ultimate strength most drastically. The three various studies is presented in Figure 5.11. The raw data for all specimens can be found in Table A1(in appendix A).

Figure 5.11 The bond ultimate strength FULT(kN) of CFRP repaired steel obtained under four different procedures of exposure to the environment.

Figure 5.10 reveals that the failure modes involved both cohesive and adhesive failure, which is similar to the failure of the specimens tested under the combined effect of environment and fatigue load see Figure 5.12. This suggests that the bonding process recommended in [7, 11, 19, and 20] is not optimal. Thus, a conclusion will be examined in more details in Chapter 6.

200C

200C

400C 0jjhk0CC00C

                 

500C 0jjhk0CC00C

500C 0jjhk0CC00C

(b)

(a)

Figure 5.12 Optical images of fatigued specimens after failure, a) with pre-exposure b) without pre-exposure to environment

5.5 A Mean for Evaluating Bond Quality Prior to Testing

The results described in the previous section revealed that means for quantifying the bond prior to testing is essential. This has been a shortcoming in several previous studies [21]. Unfortunately, “kissing bonds” and poor bond can’t be determined via standard NDI tests. To meet this challenge, Lockin-thermography, which uses Kelvin’s law to link the infra-red emission to the surface stress field, this has been widely used to study composite repairs and fatigue life extension process [15].

In this context, researchers have shown that corrosion can be detected using Lock-in infrared thermography in steel and galvanized steel panels that were coated with an organic paint. Aerospace researches have been also shown that material disbond can be easily detected using this system. Lock-in thermography involves heating the structure using a sinusoidal input of heat energy at a frequency ω, produces both amplitude and phase difference images both at the (1st harmonic) ω and also other harmonics the most relevant of which (to this study) is the 2nd harmonic 2ω. The amplitude image represents the amplitude (peak-to-peak) thermal response of the structure. The phase image is generated by phase difference measured between the input and the measured signal. The phase image is often more useful than the amplitude image for detecting subsurface defects.

In this part, Lock-in infrared thermography has been used to monitor the disbanding in the interface between CFRP and steel in DOF specimen.

To evaluate the potential of this procedure, the CFRP repairs to steel specimen was fatigue cycled, (see Figure 5.13). Figure 5.14 shows the resultant stress field. Here the dislocation in the stress field at the edges located over the joint are indicated. Such disbonds will induce adhesive failure in an aggressive environment. This test substantiates the conclusion reached in the previous experiment that the process used to bond the specimens need to be improved.

 

 

 

 

 

 

Figure 5.13: Photograph of the dofs under test

                    

                                      Side A                                                                  Side B

                   Figure 5.14 Stresses on the surface of the patch of two sides (upper adherend)

 

5.6 Designing CFRP repairs, the classical lap joint theory testing

The CMH-17-3G Composites Material Handbook [1] documents the formulae used to design bonded joints. These formulae which were validated as part of the USAF Primary Adhesively Bonded Structure (PABST) program [2], were originally developed by Dr. John Hart-Smith [3, 4]. In This formulation, it is assumed that the stresses are constant through the inner (steel) and outer (CFRP) adherends. It predicts that for a dof specimen the peak stress in the adherend occurs directly over the joint. Figure 15 reveals, that part of the PABST (Hart-Smith [15-17]) analysis is incorrect since the peak stresses actually occur slightly to each side of the joint. This feature is due to the complex 3D nature of the stress field in the dof specimen [24].

Figure 5.15 Stresses along line AB in the centre of the patch (shown in Figure 14)

The next stage in this study was analysing the stresses along the joint of dof specimen using the finite element model (FEMAP & NASTRAN software) see Figures 5.16 and 5.17.

Figure 5.16 The configuration of the half of the dof specimen using FEMAP and Nastran software

Figure 5.17 The analysing the DOFS using FEMAP and Nastran software

                 Figure 5.18: Stress at Top Surface, half of the specimen

 It is clear from the predicted stresses along the surface of the joint which resulted from using the finite element model (see figure 18), that the stress distribution have a camel hump configuration, which means that the peak of the stresses lies on either sides of the joint and not over the joint directly. This means that the FEMAP models clearly simulated the stress configuration and the results were in satisfactory agreement with the experimental results.

 5.7 Conclusions

From the investigations reported in this chapter, following conclusions can be drawn:

1)   The CFRP bonded steel specimens tested in an aggressive environment showed a significant reduction in their bond strength;

2)   By comparing the results with those presented by Borrie [11] and shown in Fig.5.11, it is clear that pre-exposure followed by an aggressive environment significantly reduces the residual strength of the bond;

3)   The failure modes involved a combination of cohesive and adhesive failure;

4)   Inspection of the bond quality reveals the presence of disbond as the adhesive touching but not bonding). Therefore, an alternative bonding process is required to get better bonding;

5)   It is clear that effective bonding process that can withstand combined fatigue-environment is required. Chapter six will examine the Boeing-USAF surface preparation procedures viz: the use of grit blast and sol gel;

6)   It has been proved experimentally and analytically that the peak of the stress in the double overlap fatigue specimen (dof specimen) lies on either sides of the joint and not exactly over the joint, and this finding is important since it contradicts the PABST formula which stated that the peak lies directly over the joint.

5.8 References

CMH-17-3G, Composite Materials Handbook, Volume 3:  Polymer Matrix Composites Materials Useage, Design and Analysis, Published by SAE International, March 2012.

Potter DL., Primary adhesively bonde d structure technology (PABST): Design handbook for adhesive bonding, USAF Technical Report, AFFDL-TR-79-3129, November 1979.

Jafari S., Singh R., Corrosion fatigue behaviour of a common AZ91D magnesium alloy in modified simulated body fluid, Advanced Materials Research, (2014), Volume 891, Issue 5, pages 267-272.

Liu, H.,Zhao XL., and Al-Mahaidi R., Effect of fatigue loading on bond strength between CFRP sheets and steel plates. International Journal of Structural Stability and Dynamics, 2010. 10(01): p. 1-20.

J. Crank and G.S. Park, Diffusion in polymers, Book, London; New York, N.Y., Academic Press, 1968.

Al-Harthi M, Loughlin K, Kahraman R. Moisture diffusion into epoxy adhesive: testing and modeling. Adsorption 2007;13: 115–20.

     Nguyen T, Bai Y., Zhao XL., and Al-Mahaidi R., Durability of steel/CFRP double strap joints exposed to sea water, cyclic temperature and humidity. Composite Structures, 2012b. 94(5): p. 1834-1845.

Baker A. and Jones R., Bonded Repair of Aircraft Structure. 1988, The Hague: Martinus Nijhoff Publishers. pp 107- 173.

Baker A. A. (2002) Introduction and overview. In: Advances in the Bonded Composite Repair of Metallic Aircraft Structure. Elsevier, p. 1-18.

                    Bai Y Nguyen TC, Zhao X-L, Al-Mahaidi R. Environment-assisted degradation of the bond between steel and carbon-fiber-reinforced polymer. J Mater Civ 2014; 26(9):1–8.

                    Borrie D, Liu H., Zhao XL., Singh R, Bai Y., Bond durability of fatigued CFRP-steel double-lap joints pre-exposed to marine environment. Composite Structures, 2015. 131: p. 799-809.

                    Matta F. (2003) Bond between steel and CFRP laminates for rehabilitation of metallic bridges, Ph.D Thesis, University of Padua, Padua.

           Zhao, X.-L., et al., Effect of dynamic loading and environmental conditions on the bond between CFRP and steel: state-of-the-art review. Journal of Composites for Construction, 2013. 18(3).

                     Fawzia, S. and M.H. Kabir. A review on environmental durability of CFRP strengthened system. In Australasian Structural Engineering Conference 2012: The past, present and future of Structural Engineering. 2012. Engineers Australia.

                    Hart-Smith, L.J., Adhesively bonded double lap joints, NASA CR 112235, January 1973.

                    Thrall EW., Primary adhesively bonded structure technology (PABST): Design handbook for adhesive bonding, USAF Technical Report, AFFDL-TR-79-3119, 1979.

                    L. J. Hart-Smith, “Further Developments in the Design and Analysis of Adhesive-Bonded Structural Joints”, Douglas Aircraft Company Paper 6992,

                    presented to ASTM Symposium on Joining of Composite Materials, Minneapolis, Minnesota, April 1980; published in ASTM STP 749.

                    M. Tavakkolizadeh and H. Saadatmanesh, “Fatigue strength of steel girders strengthened with carbon fiber reinforced polymer patch,” Journal of Structural Engineering, vol. 129, no. 2, pp. 186–196, 2003.

                    J. Teng, D. Fernando, T. Yu, and X. Zhao, “Treatment of steel surfaces for effective adhesive bonding,” in Advances in FRP Composites in Civil Engineering, pp. 865–868, 2011.

                    D. Schnerch, M. Dawood, S. Rizkalla, E. Sumner, and K. Stanford, “Bond behavior of CFRP strengthened steel structures,” Advances in Structural Engineering, vol. 9, no. 6, pp. 805–817, 2006.

                    Ahmed Al-Shawaf, Xiao-Ling Zhao, Adhesive rheology impact on wet lay-up CFRP/steel joints’ behaviour under infrastructural subzero exposures, Composites: Part B 47 (2013) 207–219.

                    X. HAN1,2, A. D. CROCOMBE1 , S. N. R. ANWAR1,3, P. HU2 , and W. D. LI2, “The Effect of a Hot–Wet Environment on Adhesively Bonded Joints Under a Sustained Load”, The Journal of Adhesion, 90:420–436, 2014.

                    Jones, R. and Paul, J., Aeronautical Research Laboratories, Australia, Structures Report 402 (1984).

                    Miller T. C., Chajes M. J., Mertz D. R. and Hastings J. N. (2001) Strengthening of a Steel Bridge Girder Using CFRP Plates. Journal of Bridge Engineering, ASCE, 6(6):514-522. (1)

                    Hollaway L. C. and Cadei J. (2002) Progress in the technique of upgrading metallic structures with advanced polymer composites. Progress in Structural Engineering and Materials, 4(2):131-148.

                    Liu H. B., Xiao Z. G., Zhao X. L. and Al-mahaidi R. (2008) Prediction of fatigue life for CFRP strengthened steel plates. Thin-walled Structures (Accepted for Publication).

                              Liu H. B., Zhao X. L. and Al-Mahaidi R. (2005a) The effect of fatigue loading on bonding strength of CFRP bonded steel plate joints. In: Proceedings of the International Symposium on Bond Behaviour of FRP in Structures, Hong Kong, China, p. 459-464.

                  Karbhari V. M., Chin J. W., Hunston D., Benmokrane B., Juska T., Morgan R., Lesko J. J., Sorathia U. and Reynaud D. (2003) Durability gap analysis for fibre-reinforced polymer composites in civil infrastructure. Journal of Composites for Construction, ASCE, 7(3):238-247.

Static Tensile Test of CFRP Laminate Repairs Steel

Temperature

(oC)

Ultimate Strength

F1ult (kN)

Ultimate Strength

After fatigue F2ult (kN)

Ultimate Strength        (kN)

(F1ave)

Ultimate Strength        (kN)

(F2ave) after fatigue

Stress Ratio

(F2ave /F1ave)

Spe1

Spe 2

 Spe 3

Spe.1

Spe 2

Spe 3

Direct Test under The Simultaneous Effect of Environment + Load

20

88

89.5

90

85

84

85

89

84

0.94

40

58

55

54

55

50

49

56

51

0.92

50

39

49

45

45

40

39

44

41

0.94

Immersed the Specimens for 2 Weeks Before the Test

20

77.5

76

80

73

72

66

78

70

0.9

40

56

51

44

42

44

45

50

44

0.88

50

33

47

37

31

Failed

33

40

32

0.8

APPENDIX A – RAW DATA FROM BOND DURABILITY EXPERIMENTS (SECTION 5.2)
 

Upper Body Tests Of Muscular Strength

Muscular strength and endurance are one of the health-related physical fitness components (ACSM, 2003). McManis, Baumgartner, & Wuest(2000)mentioned that the level of muscular strength and endurance affects an individual’s ability to perform daily functions and various physical activities throughout the life span. Upper-body strength and endurance are also considered important for performing functional and daily activities as well as preventing injury and osteoporosis.

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Because of the importance of upper-body strength and endurance, Engelman & Morrow (1991) pointed out that test developers make continuous efforts to develop different upper-body fitness test and include them in test batteries. So that the physical educators can use muscular fitness test scores to document health related physical fitness. There are many test batteries developed by different associations and available for the physical educators. Most of the include test items designed to measure upper body muscular strength and/or muscular endurance (AAHPERD, 1988; Chrysler Fund-Amateur Athletic Union[CE-AAU], 1987; Institute for Aerobics Research[IAR], 1987; PCPFS, 1987). In most of the test batteries, there will be one upper body muscular fitness test included, but some of them may provide several options for the practitioner, such as, the FITNESSGRAM® health-related physical test battery, which was developed by the CIAR(1999) and is currently endorsed by the American Alliance for Health, Physical Education, Recreation and Dance[AAHPERD], provides the following field tests for the practitioners: (a) the traditional pull-up (PU), (b) the modified pull-up (MPU), (c)the 90o push up (PSU), and (d) the flexed-arm hang (FAH). Although the practitioner may choose to use either of the tests, the PSU is recommended.
According to AAHPERD (1988); CF-AAU (1987); PCPFS (1987), PU and FAH are the most commonly used field tests as measurements of upper-body strength and endurance. But, Ross, Pate, Delpy, Gold, and Svilar (1987) argued that MPU and PU are more acceptable field tests for upper-body strength and endurance, because they can provide a better range of scores. Baumgartner, Oh, Chung, Hales (2002); Clemons, Duncan, Blanchard, Gatch, Hollander, Doucet(2004) also pointed out that modified push up test (MPSU) is commonly used to measures upper-body strength and endurance.
Statement of Problem
Many test batteries include one upper-body strength and endurance tests among the 5 tests mentioned before, or provide several options for the practitioners without any explanation.
Zhu (1998) pointed out that if test are used interchangeably, tests must be equivalent. Different tests may involve different muscle groups. According to Pat Manocchia’s Anatomy of exercise: [a trainer’s guide to your workout], PU involves biceps brachii,brachioradialis, latissimus dorsi, posterior deltoid, rhomboid, teres major and trapezius. For PSU, it involves deltoideus, coracobrachialis pectoralis major, pectoralis minor and triceps brachii. So a subject may get a high score in PSU but a low score in PU, because he/she has a very strong pectoralis major.
Sherman & Barfield (2006) pointed out that if tests are not consistent in classification, problems can occur when using test sores to classify whether the subject are in a health fitness zone.
Purpose of Study
The purpose of the study was to examine the interchangeability as well as the consistency of classification between the upper-body strength and endurance tests, including PU, MPU, FAH, PSU and MPSU by assessing the correlation between the test results among them.
Significance of Study
Mahar and Rowe (2008) pointed out that for researches, the aims of fitness test are to (a) determine the association between fitness and other health outcomes, (b) evaluate the effectiveness of training programs designed to increase fitness, and (c) determine the prevalence of adequate levels of fitness in defined population groups. In school settings, fitness tests are used to (a)provide individualized feedback to students about their fitness levels, (b) make recommendations for increasing or maintaining current fitness levels, (c) educate students about physical activity and fitness , and provide information to help determine the effectiveness of physical education programs.
Among the test manuals available for selection, there are five commonly used upper-body strength and endurance tests, which are PU, MPU, FAH, PSU, MPSU. Test manuals usually include one of these tests in their test battery without explanation on the selection. Also the test manuals usually don’t have any detailed information of the test, such as which muscle group will be assessed. FITNESSGRAM®, a test manual currently endorsed by AAPERD, allows the practitioner the option of administering any of the four upper-body strength and endurance tests, without stating their differences.
As fitness test is important for assessing subject’s fitness, hence, a subject should receive the same criterion classification regardless of what test is administered. If the tests can be used interchangeably, they must be equivalent. Misclassification of a subject may lead to an overestimation of appropriate physical activity or a discouragement in participation. Therefore, this study was designed to determine the consistency of classification, and interchangeability of the five commonly used upper-body strength and endurance tests.
Chapter 2
REVIEW OF LITERATURE
In most of the physical fitness test batteries, they include upper-body strength and endurance test, which implied the importance of upper-body strength and endurance in physical fitness (AAHPERD, 1988; Chrysler Fund-Amateur Athletic Union [CE-AAU], 1987; Institute for Aerobics Research [IAR], 1987; PCPFS, 1987).
Upper-body strength and endurance are important for performing daily functions and various physical activities. A fitness test can assess subject’s physical fitness level and help developing a suitable fitness program for the subject. But if the fitness test can not evaluate or classify the subject’s physical fitness level accurately, it may lead to over or underestimation of the ability of the subject. The present study was to determine the consistency of classification, and interchangeability of the five commonly used upper-body strength and endurance tests.
The review of literature for the present study focused on the following aspects: (a) validity and reliable of the five upper-body strength and endurance tests, (b) equivalence reliability of the tests, (c) summary of literature review.
Validity and reliable of the five upper-body strength and endurance tests
Pate, Burgess, Woods, Ross , Baumgartner (1993) studied the concurrent and construct validity of three common field tests of upper-body muscular strength and endurance including pull-up, flexed arm hang, push-up, Vermont modified pull-up and New York modified pull-up in children aged 9-10 years. The major findings are that the test performances were significantly associated with measures of weight-relative muscular strength, except push-up test, which was correlated significantly with the criterion measure of absolute strength, r(92)= .32, pMcManis, Baumgartner and Wuest (2000) studied the objectivity and stability reliability of the 90o push-up test for elementary, high school and college-age students. They gave out some recommendations on improving the objectivity and stability reliability of the test, (a) the cadence should not be too slow, (b) elementary students and low-strength college women would be more successful in performing push-ups on their knees, (c) subjects should be required to wear tight, short-sleeved shirt for better judgment on angle of elbows. Baumgartner, Oh, Chung and Hales (2002) also suggested that women and very young individuals should execute push ups on the hands and knees. Besides the clothing, they pointed out that hand placement must be specified in the push-up test protocol.
Romain and Mahar (2001) determined the test-retest reliability and equivalence reliability of the push-up and the modified pull-up tests from both norm-referenced and criterion-referenced frameworks. Sixty-two students aged between 10.5 and 12.3 years were administered the push-up and modified pull-up tests. The criterion-referenced test-retest reliability estimates were high for both tests, but the equivalence reliability estimates were considerably lower between them. Also the criterion-referenced equivalence reliability findings were not acceptable.
Clemons, Duncan, Blanchard, Gatch, Hollander and Doucet (2004) determined the relationships between flexed-arm hang and select measures of muscular fitness, which are absolute strength (1RM lat pull down), relative strength (1Rm/mass) and muscle endurance (repetitions to failure at 70% of the 1RM). Sixty college-age women were studied and the results showed that FAH is a test of weight-relative muscular strength and appears unrelated to absolute strength or muscle endurance.
Equivalence reliability of the tests
Pate, Burgess, Woods, Ross, and Baumgartner (1993) found that the performance on the five field tests(pull-up, flexed arm hang, push-up, VMPU and NYMPU tests) were only moderately intercorrelated. The highest interest correlation was between flexed arm hang and VMPU tests, r(92)=.71, PRomain and Hahar (2001) were the pionners to study the criterion-referenced equivalence reliability estimate between push-up and modified pull-up tests among young children. They found that the classification agreement between push-up and modified pull-up tests was low. Also they pointed out that because the FITNESSGRAM® allowed the physical activity directors to choose among four tests to measure upper-body strength and endurance, the criterion-referenced equivalence reliability of these tests should be examined.
Sherman and Barfield (2006) studied the equivalence reliability among the four upper-body strength and endurance tests(Push-up, pull-up, modified pull-up and flexed arm hang) in FITNESSGRAM®. 383 children in Grades 3 to 6 were tested over a week. The result showed that the equivalence reliability between PSU and MPU was acceptable for boy, but unacceptable for girls. The classifications for boys aged 10 and 11 regarding the push-up and pull-up tests were not consistent, but they were consistent for girls, except age 11.
Summary of literature review
Upper-body strength and endurance are important for daily functional activities. A valid upper-body strength and endurance can accurately assess and classify subject’s muscular fitness level. This information can help physical educator the develop suitable fitness program for the subject.
The above studies shown that the five field test are valid for measuring weight related strength rather than absolute strength and endurance. Also, for the equivalence reliability among the tests, there is lack of study on college student.
Definition of Terms
The following terms were defined operationally:
Health-related physical fitness
According to American College of Sport Medicine (2003), health-related physical fitness actually has four components: aerobic fitness, muscular fitness, flexibility and body composition. Muscular fitness is the strength and endurance of individual’s muscles.
Muscular Strength
Docherty (1996) stated that the International System of Units (SI) defined strength as the maximal force or torque developed by a muscle, or muscle group, during one maximal voluntary action of unlimited duration at a specified velocity of movement.
Muscular Endurance
Docherty (1996) defined that muscular endurance is the ability of a muscle, or muscle group, to generate force repeatedly or for an extended period of time.
Pull up
According to AAHPED (1988), Pull up was defined as a person using overhand grip, body completely extended, raise until chin clears bar, then lower to full hang as in starting position.
Flexed arm hang
AAHPED (1988) defined Flexed arm hang as a person using overhand grip and in a position with chin clearing bar, elbows flexed, chest close to bar and hold this position as long as possible.
Push up
Chrysler Fund-Amateur Athletic Union (1987) defined push up as a person in prone position, elbows bent, hands flat on floor, thumbs pointing inward and next to chest, then pushes body up until elbows are straightened, while heels, hips, shoulders, and head remain in the same straight line.
Modified pull up
Pate, Ross, Baumgartner (1987)defined it as a person in supine position, the bar adjusted just out of reach of fully extended arms. That person grasps bar with overhand grip, maintaining arms and legs straight, feet together. Then pull up the body with arms so chin clears the bar.
Fatigue
According to Rod et al. (2006), fatigue is defined as the decreased capacity to do work and the reduced efficiency of performance that normally follows a period of activity.
Research Hypothesis
According to the above literatures reviewed, it was hypothesized that:
1. There would be no significant correlation between the
five upper-body strength and endurance test results. And the classification is not consistent.
Chapter 3
METHOD
The purpose of the study was to examine the interchangeability as well as the consistent in classification of the upper-body strength and endurance tests, including PU, MPU, FAH, PSU and MPSU by assessing the correlation between the test results among them. This chapter was divided into the following parts: (a) subjects; (b) procedures; (c) method of analysis; and (d) statistical hypothesis.
Subjects
This study was targeted to male college students, who were studying in Hong Kong Baptist University and aged between 19 to 25 years old. Subjects will be selected by convenient sampling. Before the study, subjects was asked to sign on the consent forms after knowing the purpose, benefits and risks of the study.
Procedures
In this study, subjects were invited to perform the five upper-strength and endurance tests in a specific sequence, which is pull-ups, push-ups, modified pull-ups, modified push-ups and flexed arm hang. Test and retest were held on two separate days with in a week. All tests will be conducted in the fitness room of Hong Kong Baptist University or the fitness room of LCSD.
The subjects were strongly advised not to have a heavy meal 2 hours before the sit-up tests. The subjects were invited to do warm up exercises. Warm up exercises included 5 minutes jogging or cycling and then 5 minutes related stretching exercises. After the warm up exercises, subjects were invited to perform the tests.
The description of the pull-ups, push-ups, modified pull-ups and flexed arm hang tests were described by the FITNESSGRAM® (2007):
Pull-ups
The subject should start will hanging position an the bar with an overhand grasp. The subject uses the arms to pull the body up until the chin is above the bar and then lowers the body again into the full hanging position. The exercise is repeated as many times as possible. There is no time limit.
Push-ups
The subject should begin with a prone position with hand place under or slightly wider than the shoulder, fingers stretched out, legs straight and slightly apart, and toes tucked under. Then pushes up of the mat with the arms until arms are straight, keeping the kegs and back straight. The subject then lowers the body using the arms until the elbows bend at a 90o angle and the upper arms are parallel to floor. This movement is repeated as many times as possible.
Modified pull-ups
The student grasps the bar with an overhand grip. The pull up begins in this “down” position with arms and legs straight, buttocks off the floor, and only heels touching the floor. The student then pulls up until the chin is above the bar. The subject then lowers the body to the down position. Movement continues in a rhythmic manner.
Flexed Arm Hang
The subject grasps the bar with an overhand grip. With the assistance of one or more spotters, the student raises the body off the floor to a position in which the chin is above the bar, elbows are flexed, and the chest is close to the bar. The position is held as long as possible.
Modified Push-up
The subject should begin with a prone position with hand place under or slightly wider than the shoulder, fingers stretched out, legs straight and slightly apart, and knees tucked under. Then pushes up of the mat with the arms until arms are straight, keeping the legs and back straight. The subject then lowers the body using the arms until the elbows bend at a 90o angle and the upper arms are parallel to floor. This movement is repeated as many times as possible.
There will be three minutes rest between each test.
Delimitations
The following delimitations were included in this study:
The subjects of the study were delimited to the male students who were studying in Hong Kong Baptist University and aged between 19 to 25 years old.
All the tests were carried at the fitness room of Hong Kong Baptist University or the fitness room of LCSD.
The test and retest were held in separate days within a week.
Data Analysis
Statistical hypothesis
The following null hypothesis was examined:
1. There would be significant correlation between the five upper-body strength and endurance test results. And the classification is consistent.
Statistical Analysis
Data were reported as mean and standard deviation. Minimum and maximum values of variables were analyzed by the Statistical Package for Social Science (SPSS). Pearson Production Moment Coefficient of Correlation (r) was used to examine the correlation between the 1-min sit-up result with that having fixed frequency and no time limit. An alpha level of pLimitations
The following limitations were included in this study:
1. The subjects are restricted to the students who can use the fitness room of Hong Kong Baptist University or LCSD.
2. The motivation of the subjects in performing the tests, as all the tests are with no time limit, was uncontrollable. It might affect the results of the study.
3. The performance of the subjects might be affected because of their physical lifestyle and the physical activity level.
4. The performance of the subjects might affected due to their different physical characteristics.
Study findings are applicable only to the subjects included in this study.