Lloyd’s Building

Construction planning is a basic activity in managing and executing construction projects; it is a challenging field that requires detailed planning and being in tandem with technology and use attributes for the building. Planning and executing a building requires taking into consideration the choice of technology to use, the underlying building concept, materials, and the structure’s life cycle as well as how these interact. One of the important concepts in modern building construction is the concept of the overall frame and the services in a building. Buildings now requires services for heating, lighting, ventilation, air conditioning, and lifts, and with the demands on energy sources, energy efficiency (Thallon, 2016). Builders are also keen to keep the costs of construction low, as one of the approaches to attaining green building aspirations. The frame of a building pertains to the fitting together of material pieces to give the structure shape and support; with the commonly used materials usually being engineered wood, standard wood, or structural steel (Baldwin & Bordoli, 2014).

Framing has two main categories, light frame and heavy framing. Heavy frame construction, as the name suggests, pertains to very heavy vertical supports for the  building, and features such materials as steel framing and pole building framing. Light frame construction, on the other hand, is the opposite and is characterized by the use of standard lumber with minimal materials used to achieve cost reductions and to have a large area enclosed at minimal costs. Light frame structures are further given strength using materials such as plywood (Alen & Iano, 207), (Thallon, 2016). This paper discusses the two aspects of construction; frame and services by evaluating two buildings located in the UK- the Gherkin (The 30 St Mary Axe) building located in the City of London, and the Lloyd’s building, located also at the City of London, on Lime Street. Comparisons will be made on the two buildings based on frame and services and sketches as well as images of the building structures also made.

The Lloyd’s building is an apt demonstration of the concept of Bowellism where the interior of the building is designed for maximum uninterrupted space while the building services, including the lifts and air conditioning, are located in the exterior. The architectural firm, Richard Rogers and Partners designed and built the structure between 1978 and 1986 (Lindner & Schneider, 2017). The structure of the building is strength / vertical with a rolled steel profile in which the steel columns cross section are ‘I’ shaped and its wide column flanges are wider and thicker than the beam flanges; this is designed so that the building can withstand compressive stresses  better. Further  tubular and square steel sections have also been used and reinforced using concrete, with bolts used for connecting the steel beams to columns, with rivets and threading also used as connectors (Kroll, 2010). Because higher bending moments are likely to be experienced in the beams, the central “I” shaped steel webs are are wider that the steel column web to resist the bending forces better.

Gherkin

Looking the Lloyd’s building, the use of a perimeter steel frame that is rectangular can be discerned. The building is characterized by a large rectangular central space surrounded by three services tower lifts and three main towers. Because of the Bowell nature of the design, the center of the building has high steel galleries that reach up to 60 meters; on top of which there is a barrel vaulted glass roof to provide natural lighting (Lyon, 2006).  The galleries open to an atrium that are interconnected using escalators running in the middle of the structure. However, to reach the higher floors, one has to use the external services (lifts), with facilities like Internet cabling  also located on the exterior of the building. At its highest point, the building is 88 meters and there are various service cores on top of which are found cleaning cranes. The overall structure of the building plan is modular and each floor can be altered easily through addition or removal of walls and partitions (Kroll, 2010).  The image below shows the modular structure of the building fram.

The overriding factor in the design of the building was flexibility with uninterrupted space, factors that gave rise to the building and it is designed so that maintenance activities and cleaning do not interrupt daily operations. The spaces are grouped, using its modular design, into service towers for the stairs, elevators, bathrooms, and machinery rooms; the towers are found on the exterior of the building. The site of the building was very irregular, hence the need to use the modular Bowell design with services, including lifts on the exterior to maximize the use of the available space. The main body of the building is rectangular, yet the plot it is situated on is trapezoidal, hence the use of external services is very innovative. The services have been designed in such a way that they can be easily accessed from outside of the building; this implies that needs for changes of improvements can be done; or augmented, with minimal fuss to the daily operations of the building. For instance replacing ventilation shafts need not interfere with the daily operations inside the building (Booth, 2014).

The building’s main structure is made of reinforced concrete with main pillars and augmented with steel; this means the building can still be expanded upwards (vertically).  The tower structure consists of beams, pillars, and slabs and are all prefabricated; implying that its design and construction was futuristic, using prefabricated materials assembled on site. The perimeter and core of the building is primarily made of reinforced concrete while the central building body is made up of a few 10.8 x 18 m modulated mesh pillars, all encompassed within an independent coating stage system that consists of three glass layers with one ventilated layer. The outer skin of the building is triple glazed  to act as an air tube, running the entire vertical length of the building from the floor to the ceiling. Within the coating are sandwiched stainless steel panels that act as fire retardants. Because of its innovative frame and services design, the Lloyd’s building has been given a Grade I Listing, becoming the ‘youngest’ building to receive the accolade (Waite, 2011). Below are images of the building; both complete and structural to show its frame and services construction and placement, respectively. 

Comparison

Lloyd’s building showing the rectangular steel perimeter frame used in its construction.

Modular structure for the building

Rectangular Frame

For the Lloyd’s building, the bowell design naturally means services that include elevators are found freely concentrated on the exterior with cabling and heating, ventillation, and air conditioning alos running along the exterior of the building as shown in the image below;

Services

This is a 180 meters, 41 stories high building also located at the City of London on St Mary Street, with an overall contemporary architecture and was built to replace the earlier Baltic Exchange and Shipping Chamber building that was extensively damaged by a bomb in 1992, and was completed in 2003 by Skanska (Solomon, 2008). Unlike the Lloyd’s building, the Gherkin has a diagonal grid frame where concrete, metal, and wooden beams are used in a diagonally intersecting manner. The design of the building frame as diagonal grids has both aesthetic and functional applications; the diagonal grid frame ensures reduced use of materials, especially steel. For this building, 20% less structural steel was used than would be possible with a conventional rectangular steel frame (Fu, 2015).

Unlike the Lloyd’s building where columns must be used for structural integrity, the Gherkin with its diagonal grid eliminates the need for columns to provide structural support for the building; further, the roof expanse is made without the need for columns to support it as the diagonal grid frame is ‘self supporting’. The A-shaped diagonal frames provide load bearing that is well distributed, resulting in a structurally strong building with less use of structural steel. The building structure also has a core whose job is to resist gravity loads with diagonal grids and nodes used at connections for rigidity and strength. The building is designed such that the floor plates can rotate 5 degrees; this is made possible by its column-less frame design. The wells are light and are generally wedge shaped. The building is made using tube steels that are coated with Aluminum to form the diagonal grids, arranged end to end; a full diamond of the diagonal grid A frames covers four floors (Gunel & Ilgin, 2014). The image below shows the diagonal grid (diagrid) frame and how it works in load bearing.

The diagr system works on the principle of vertical cantilever with dividing the tower’s height into modules to determine its size. Because the tubes used in the diagrid are not by themselves strong enough to achieve the desired stability, they are connected to the edge of the floor and to the core using a ring beam. The building is designed using a frame structure so that the very top resists shear forces while the base resists moments. Within the diagrid, the diagonal members absorb the moment and shear forces (Kara, 2013).

Materials and Construction Techniques

Compared to a triangular frame structure like Lloyd’s, the diagrid frame structure of the Gherkin gives a cylindrical shape that is aerodynamic in nature, enabling wind to move around the building rather than encounter resistance as happens with the Lloyd’s building frame as depicted above. By having a cylindrical shape occasioned by the diagrid frame, the building is able to decrease buffeting, diminish fluttering, and reduce vibrations’ as the image above shows, W represents wind while M represents movement; comparing the two demonstrates why the diagrid design is better at managing wind loads with significantly less structural steel and no supporting columns (Ching,  Onouye, & Zuberbuhler, 2014).  Lateral air loading is managed by the glass facade on the exterior that transfers the load to the diagrid frame because of the natural ventilation system achieved by the diagrid structure trough a double skin. While the rectangular frame Lloyd’s building provides maximized space and external services that cause little or no disturbances to interior activities, the diagrid frame provides a unique structural form that results in significant reductions in energy use, natural ventilation, ad increased resistance to shear and moment forces and responds well to both internal and external loading.

The building has a special and unique design to minimize energy consumption and allow natural internal climate control and regulation. Its very frame is energy saving, and it means the building utilizes half the power a similar building tower can use. In every floor, gaps have been left resulting in six shafts that form a natural system of ventilation for the whole building, albeit being with interrupting fore breaks every six floors; otherwise, it forms a chimney for air conditioning running through the entire vertical length of the building. The building’s shafts perform an important role of creating a double glaze effect where air is sandwiched between two glazing layers; this provides sufficient insulation for the spaces in the building, resulting in drastic reductions in energy consumption. The double glazing helps avoid heat convection across narrow gaps between panes, which is an inefficient process; however, using the diagrid frame, this process is highly exploited. Warm air is pulled out of the building by the shaft when it is hot (like in summer) and during winter when it is cold, the building interior is warmed by the shaft through passive solar heating (Thallon, 2006).

Further, the shaft attained using the diagrid structure enables natural light to pass through the structure, keeping low lighting needs and making it a natural environment structure. Because of lack of supporting pillars, the building would be prone to wind shears and swaying; to control the risk of swaying from wind, the stiffness of the diagrid structure is increased with active tuned mass dampers used for damping. The diagrid frame is a triangular perimeter structure that helps to make the building stiff without the need for using extra reinforcements. The services that include the lifts,  cabling, and escalator are contained within the building, unlike the Lloyd’s building in which these are found on the exterior to maximize space. However, because the Gherkin building also does not have supporting columns with the diagrid frame providing load bearing and support, it also maximizes the space inside the building, through the tapering top naturally reduces its usable interior space when compared to the Lloyd’s building. The main services include heating and air conditioning and the elevators. The elevator services are located within the building core, with a total of 18 lifts for passengers, elevators for fire fighting services and for goods, and a car park elevator that brings cars from the basement to the reception area. The centrality of the elevator services in the core gives the building stability and allows better access to them while leaving most of the space for functional use, as depicted below;

Other services including HVAC are also located within the building’s core to maximize space utilization

References 

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Thallon, R. (2016). Graphic guide to frame construction. Newtown, CT : The Taunton Press

Waite, R. (2011). Rogers’ Lloyd’s becomes youngest Grade-I listed building. Architects Journal. Retrieved 9 January 2018, from https://www.architectsjournal.co.uk/home/rogers-lloyds- becomes-youngest-grade-i-listed-building/8624035.article