Designing the Chenab Railway Bridge

Indian Railway Corporation embarked on a huge development of building of a novel rail line route between in the Municipal of Jammu and Kashmir, between Udhampur and Baramulla. The venture had been professed as a countrywide development scheme. The arrangement comprised of several tunnels and bridges that were to be executed in extremely rocky and hilly topography, with the problematic Himalayan geology Pulkkinen, etal. (2012). The infrastructure crosses a profound valley of the River Chenab that required building of a long-span bridge. The Bridge is situated in the Jammu and Kashmir region in the northern front of India

It runs across the Chenab Water body neighboring the rural community of Kauri. It is a subproject of the new Baramulla−Srinagar−Udhamptur rail line construction. The total length of the bridge is 1315 metres. The free span length of the bridge is 467 metres, measured from the seeming beneath of the river, the stature of the bridge deck is 350 metres. As a consequence, Bridge Chenab is the largest and longest-spanning rail line bridge of its kind in worldwide. It holds nearly 25,000 tons of steel.

 The Chenab Bridge was planned to be finalized by the end of December 2009. However, In September 2008 it was publicized that the development Scheme was stopped temporarily even with the accomplishment of groundwork of the approach viaduct India, (2008). Starting mid-2009, it was agreed that the initial course to resume and the bridge would be constructed as initially scheduled. On the other hand, it was decided that the key length of the bridge would be revised to be 467 m. Chenab Bridge is an arch bridge entirely made of steel.

Also the sundeck of the bridge is out of steel. Bases and the approach overpass piers are out of concrete. The arch was built by means of a cableway crane. In actual fact, all the assemblage links are bolted. The quantity of bolts is about 600,000. The structure is established on the bedrock. The bases of the arch are roughly 40 m tall and 50 m wide.

Preliminary Design

The Chenab Bridge is situated in seismically active region. Owing to the tunneling effects in the valleys, the site also experiences high wind forces. To endure this, a preliminary design and as series of tests were conducted in Force Technology Laboratory in Denmark. The preliminary design was executed to find out the most feasible (economical, long lasting, and most efficient) type of bridge and method of construction. Mitchell, (2008). 

Functional criteria

Preliminary design of the key bridge necessitude contemplation of several extra considerations, such as composite action, fatigue, secondary demand effects, global stability etc. It as well required that such a special bridge is calculated to realize a reliable degree of dependability for all force cases, and that design principles equal the building principles.

A series of studies were carried out to determine the most appropriate properties and sections. First, Wind characteristics were considered in-depth in the first portion of the wind-tunnel analysis platform with big size scale model of the landscape. The study was envisioned to define the exact design wind speed.

Preliminary Design

 Secondly, section-model test were carried out to achieve smooth input for wind forces and investigative wind-caused vibration reaction working out. Thirdly, Deck unit was analyzed also with aero elastic analysis to find factors for vortex-caused vibration inquiry. Two deck forms were investigated: with and without wind nudging. The design approved the one bearing the nudging owing to lesser horizontal force coefficient.

Design engineering activities

The investigative wind reaction calculation was carried out by multimode frequency-domain exploration by considering the outcomes of the topography and unit prototype assessments. Static corresponding wind forces were consequential for operational engineer to utilize in modelling of the work-related bridge and building phases. Lastly, the scrutiny and wind-resistance of the accomplished bridge was established with complete aero elastic model test.

After a chain of studies for several options like cable stayed bridge and arch bridge, the client (Kon Kan Railway Corporation) zeroed in on the preference of arch bridge and the same has been identified as a rudimentary structural configuration for the Chenab Railway Bridge.

Detailed design

Generally a bridge is examined as a plane structure. For that reason, only 3 elementary equalities of symmetry, ought to be gratified conferring to the functional mechanism. These equalities are as:

∑F_X=0,  ∑F_Y=0,            ∑M=0,

Any building satiating these 3 equalities is a practicable building. If a building flops to fulfill these 3 equalities is not realistic. On the other hand, a bridge is not a 2-dimensional assembly despite the fact that it is evaluated as a 2-dimensional assembly often. This deliberation of 2- dimensional examines for bridges is utilized for easiness and is recognized internationally.

Design requirements

The bridge Proprietor set stern instructions and principles that were to be complied within the design. Indian Rail line Principles (IRS Standards) had to be utilized where valid. British Standards, Eurocodes and other international standards as well as UIC Standards could be utilized as a complement.

Below are selected design standards taken used in the design of the bridge:

• Limit state values of modelling had been agreed to be charted in accordance with British Standard (BS) codes
• Calculation of wind load special effects in accordance with wind tunnel assessments
• Site detailed seismic ranges technologically advanced by Indian Institute of Technology (IIT) Roorkee
• Establishment of Euro code 8 for ductility describing of towering and muffled rectangular RCC piers
• Establishment of long welded rail (LWR) over the structures and consequential force determination in accordance with UIC – 774-3R guiding principles
• Blast resilient modelling has been utilized
• Design inspection for fatigue in accordance with British Standards (BS) codes
• Distortion restrictions in accordance with principles of UIC – 776-2R and UIC 776 -3R course of action
• Redundancy made available in the buildings, for lesser level of task in the course of misfortunes and contrary to breakdown in extreme cases of one pier failure.

 The design speed of the rail line was agreed to be 100 kilometres per hour and the design lifespan set to be 120 years. Lethargy calculation was executed in accordance with BS: 5400 Part –10. Wind forces were consequential by means of bodily terrain models of the place and assessments in a wind tunnel test center. Even full-scale prototypes were mandatory. The analysis outcomes of the structure were utilized to source corresponding static wind forces that were utilized in the concluding structural scrutiny.

These corresponding static wind loads describe wind-caused vigorous activities of the structure, along with size decrease effects related to the sporadic spreading of wind pressure points. The facility wind load tallies to an extreme wind pressure of 1500 Pascal. The wind load is leading the arch design. Beside small straight rail line bridge forces, this bridge had to withstand special blast loads indicated by the Customer, and to be responsible for satisfactory redundancy in case of confined catastrophe. The utmost significant design principle in the steel deck is fatigue. National Steel Bridge Alliance, (2009). 

Functional Criteria

Evolution of design detail.

An extraordinary blast load had to be well thought-out in the design. The structure would be designed for two circumstances of blast happening on the deck or in the vicinity of the bases.

-> The arch trusses should not be spoiled and no bridge length should ruin in such conditions. Whichever harm on the building should be mendable so as to be reinstated to its innovative serviceability condition National Steel Bridge Alliance, (2009).

Another extraordinary loading case originates from the necessity of structural redundancy. The scheme will be evaluated by eliminating precarious single structural elements in sequence. These fundamentals are:                                                                                                                                                  one minor chord of the arch truss (1box out of 8 boxes founding the entire arch) of a maximum of. 8 m long stuck between the trusses joints. Side rise of the Bridge Chenab. The arch and arch piers of Bridge Chenab would be made out of huge steel trusses.

Integration of subsystems

In order to offer least wind opposition, it was originally planned to utilize pipe segments for each and every member of the arch. For simplicity of the manufacture on spot, the chords of the trusses and the diagonals were later changed to turn into closed steel boxes. Railway Technology, (2018).  The rest sections comprising of the secondary sections were retained round that significantly make things easier when joining details.

The chord sections would be packed with concrete to support in governing wind-caused loads on the structure by refining the damping ratio and stiffness. The concrete seal also improves the whole sturdiness. In the arch region, the framework is held by steel piers with a stature equal to 120 m. Expansion joints are located at the close of abutments and at Pier S70 that splits the central arch length from the approach bridge. At this position there is an alteration in the deck stature.

Design tools

All the bridge assemblies were 3D molded. The steel structures were modeled extremely precisely, e.g. the model enclosed welding grooves in detailed form. The diagrams to produce the steel building were published unswervingly from the structure data model Thomas, (2012). The geometry of the structural analysis model was imported in pre-elevated form, based on which modeling continued. Rock surface was modeled to use as a reference in the model. This long-term project was modeled using Tekla Structures version 19.0. Data transfer was challenging at times because this version does not support Tekla Model Sharing functionality which would have been useful due to long distances and poor web connections in the remote areas in India. Railway Technology, (2018)

Evaluation and validation of Chenab Bridge

An all-inclusive evaluation on both deterministic and probabilistic danger analyses was executed for the Chenab bridge position. The chief conclusions are summarized below:

1. i) The Chenab bridge setting is located in the tectonically active Himalayan zone falling under zone IV. Eighty two seismo tectonic topographies such as faults/thrusts were acknowledged that may cause significant future earthquakes within 350 km radius of the Chenab bridge site.
2. ii) Out of these tectonic topographies, 20 of them were well thought-out as major and their source lengths changing from 4.82 to 947.97 km.

iii) Wells and Coppersmith’s (1994) model was utilized to forecast magnitudes (Mw) from the rupture distances for all faults.

Validation

 Slope was designed with surface mapping. Every time the experts progressed to next bench on sequential critical validation was arranged. The innovative alignment was checked with designed alignment. If any noticeably variation perceived in alignment concerning designed alignment it required redesign. The validation of each 5m depth was reiterated at least for first two sequential statures before proceeding to next level. National Steel Bridge Alliance, (2009). 

Conclusion

In the design of the Chenab Bridge, special deliberation on a number of extra special constraints such as fatigue, composite action, second order effects, and global stability was done.

The Chenab Bridge is the leading, longest-span and the uppermost railway arch bridge interminably constructed worldwide. Its design presented great trials to the design team, but the difficulties were even more challenging before the gap between the main arch splits was filled.

Reference.

India. (2008). Indian Railway Catering and Tourism Corporation Limited: Ministry of Railways. New Delhi, Lok Sabha Secretariat.

Mitchell, S. K. (2008). The longest bridges. Milwaukee, Wis, Gareth Stevens Pub.

National Steel Bridge Alliance. (2009). World’s longest bridge spans. Chicago, Ill, American Institute of Steel Construction. A

Pulkkinen, P. etal. (2012) Conceptual design of the Chenab Bridge in India. Procedia Engineering, 40, pp. 189-194.

Railway Technology, (2018) Chenab Bridge, Jammu and Kashmir, India, [online]. Available from: https://www.railway-technology.com/projects/chenab-bridge-jammu-kashmir/ [Accessed on 25 September 2018].

Thomas, M. (2012). The Chenab Bridge: world’s longest bridge. New York, PowerKids Press. Available from: https://www.myilibrary.com?id=221169. [Accessed on 25 September 2018].