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The Shard
London Bridge Street, Southwark, London, UK
The Shard
associated engineer
WSP Cantor Seinuk
date  March 2009 - November 2012
era  Modern  |  category  Building  |  reference  TQ327802
photo  © Chris Talbot (cc-by-sa/2.0)
The Shard (London Bridge Tower) is London’s tallest building (2016), a tapering glass spire that reflects the city's changing skyscape. It is located on a brownfield site at London Bridge railway station, and was designed as an energy efficient "vertical city" for up to 8,000 people. Its creation benefited from innovative techniques such as top-down basement construction, and from inventive craneage.
In July 1998, the British government issued a Parliamentary white paper, A New Deal for Transport: Better for Everyone, setting out policies for an integrated transport system. One of them was to encourage the development of tall buildings at major transport hubs, such as railway stations.
In November 1998, property developer and entrepreneur Irvine Sellar (b.1939) acquired the previous building on this site. Southwark Towers (1975) was a three-winged, 100m high concrete frame office building, south west of London Bridge Station, on the south bank of the River Thames. The station is one of the city’s busiest hubs, with about 54 million passengers annually (2013). It operates national rail, London Underground and bus services, and a cycle park.
Before World War II (1939-45), a succession of 19th century railway structures had occupied the Southwark site. Today, the railway lines are still carried on the extensive original brick viaducts, at about 9m above ground level, constructed to enable trains to cross inner London's streets without level crossings.
In May 2000, Sellar met with Italian architect Renzo Piano (b.1937) to explore ideas for developing the site into what Sellar described as "an architecturally striking vertical city". Though not keen on designing tall buildings, Piano was inspired by the site and began to sketch. With his practice Renzo Piano Building Workshop, he developed the design for a pyramidal tower, reported inspired by church spires and the masts of sailing ships.
Initially, there was opposition to the development plans, with English Heritage's claim that the building would be "a shard of glass through the heart of historic London" giving the structure its name. After a planning inquiry, consent was granted on 19th November 2003.
The superstructure of Southwark Towers was demolished in 2007-9 and the site cleared, though the building’s under-reamed foundation piles were left in place. Construction of the Shard commenced in March 2009.
The Shard is a narrow pyramid, 309.6m high, with sides sloping at six degrees. Its tapered shape works hand-in-hand with the concept of a multifunctional vertical community. The large floor plates of the lower storeys suit reception areas (ground floor to level 2) and offices (levels 3-28) to optimise communications. The intermediate storeys suit hotel use (levels 34-52), which requires a core corridor and perimeter rooms. Apartments occupy the smaller upper floors (levels 53-65) with the best views. Above level 72 is an unoccupied jagged spire. Plant is located at levels 29, 75 and 87.
The building structure also changes with level. The three basement levels are concrete frame, ground to level 40 is steel frame, levels 41-69 concrete frame (lower levels post-tensioned), and the rest of spire steel frame. The reinforced concrete core extends to level 72.
Site ground conditions consist of made-up ground near the surface, over layers of alluvium and permeable river gravels, with London Clay at a depth of some 9m. Below that are layers of Lambeth Group Clay, Lambeth Group Sand and Thanet Sand. A north-south fault in the strata has resulted in the base of the London Clay and other strata being about 5m lower to the east of the fault than to the west, so longer piles were required on the east side of the site.
In addition, the existing piles from the demolished Southwark Towers, which had no basement, extend only a few metres below the level of the Shard's lowest slab. It was not economic to extract the old piles, so new ones were designed to pass between them. Other subterranean obstacles included a disused stair shaft inside the building footprint, a disused lift shaft on the boundary, London Underground tunnels 5-10m from the north west corner of the basement, a ventilation shaft in Joiner Street to the west, and assorted utility infrastructure in adjacent streets.
The demolition of Southwark Towers, basement excavations and the construction of the Shard's superstructure were all predicted to cause movement in the ground, railway viaducts and surrounding buildings. One of the UK’s largest finite element models forecast heave of up to 12mm and settlement of up to 27mm. However, extensive real time monitoring throughout the project revealed the actual movement was less than anticipated.
Foundation construction began with the sinking of bored piles, 1.5m and 1.8m in diameter, up to 53m deep. The piles are cased through the alluvium and gravels, while bentonite grout supports the bores in the water-bearing Lambeth Group beds and Thanet Sands. Many of these bearing piles contain steel plunge columns some 500mm square to support the building's core, superstructure columns and basement slabs — installed by a specially developed, hydraulically controlled, laser-guided rig to a vertical accuracy of 1:400 and within 15mm of the specified top level. The bores are also filled with concrete.
The three-level basement was built top-down within a retaining wall of 900mm diameter interlinked secant piles at 750mm centres. A vertical tolerance of 1:200 was specified for the secant piles, to ensure full interlocking, and 98 percent of them achieved this. The top-down construction sequence meant casting the ground floor slab first, excavating beneath it to level B2, casting a slab there and continuing the excavation to level B3, then casting a raft foundation.
The eastern end of the basement is double-height, so the level B1 slab only covers part of the footprint. The core walls begin at level B2. The heavily reinforced raft at B3 is supported on the bearing piles and London Clay. The top of the slab is 13·3m below ground, 3m deep beneath the core and 1·5m thick elsewhere. This raft was the UK's largest ever continuous concrete pour — a total of 5,500 cu m placed in 36 hours.
For the raft, 70 percent of the cement content has been replaced the ground granulated blast furnace slag. Pulverised fuel ash replacement has been used in concrete elsewhere in the building. Together with the minimum-weight design of concrete and steel, these replacements help reduce the building's total embodied energy and carbon footprint.
The core was constructed using slip-form techniques, with self-compacting concrete poured around the reinforcement in the lowest levels. The slip-former was erected at level B2 and the shutter moved upwards by hydraulic jacks. Locating the shutter with GPS (global positioning system) techniques achieved a plan accuracy of 25mm. As the core was grew, simultaneous basement construction continued below it. At one stage, the core plunge columns were supporting 23 storeys (levels B2 to 21).
The core is designed as a vertical cantilever, enabling it to withstand lateral loads. For the lower floors, the size of the core and the arrangement of its shafts for lifts and stairs provides all the strength and stiffness required. To optimise available space, office lifts have double-deck cars and some shafts are stacked — high-level lifts above low-level ones — with transfer structure at levels 34-37 over a lift lobby. There are 44 lifts in total, travelling at up to 6m/sec.
The tower crane working up through the top of the core was attached to the slip-former rather than the core itself. Suspending it from the interior shutter eliminated the need to stop slip-forming periodically to move it. The crane was kept vertical by wheels at the base of its mast running along guide tracks in one of the shafts.
To increase office floor area, a vertical-sided 19 storey extension was constructed up to the site boundary at the south east corner of the main building. A smaller core in the extension houses additional lift and stair shafts, and further increases the torsional resistance of the whole building.
Steel embedment plates were cast into the sides of the main core during slip-forming, to provide connections for the steel floor beams. The outer ends of the beams are connected by substantial steel edge beams, supported on perimeter columns. The edge beams were lifted into place complete with pre-installed safety handrails, an 8mm steel plate to support the edge of the concrete floor slab and channels for the cladding brackets.
The floor beams consist of welded plate girders, with flanges varying from 150 x 10mm to 500 x 70mm, and webs between 8mm and 40mm thick. Services are routed longitudinally between beams and transversely through fabricated holes in the webs. The beams span up to 15m between the core and the perimeter columns.
The majority of beams are 500mm deep. Heavily loaded primary beams up to 650mm deep are aligned with the bases of the others, with the top flange protruding into the floor slab to maintain a constant ceiling void. The beams act compositely with the concrete floor slabs, which are generally 130mm lightweight concrete on metal deck, though the plant floors are deeper and of regular concrete to provide acoustic separation. From the raised floor surface to the underside of the ceiling below, the typical ceiling zone is 950mm deep.
Above the offices, services are routed above the corridors around the core, with risers on the outside of the core. As the building tapers, the span from core to perimeter columns reduces to 9m.
In the upper concrete frame section, a combination of 200mm post-tensioned flat slabs and shallower finishes reduced the storey height by 650mm, compared with the composite floors, and provided acoustic separation and structural damping against wind loading. Two additional floors were able to be inserted without changing the overall building height, which was limited by the Civil Aviation Authority.
Fewer shafts ascend to the intermediate floors, so the core’s inertia was increased by adding projecting wing walls between service risers. At levels 66-68, stiffness is increased and sway controlled by a truss of diagonal steel members spanning between the core and the perimeter columns. The truss members were not connected until the whole structure was complete to avoid the effects of differential axial forces (the core has a much bigger cross-section than the perimeter columns).
Perimeter columns for the floor framing system are of steel up to level 40, reinforced concrete for levels 41-72, and steel again for the spire. The columns follow the line of the façade, so most are inclined, though some have vertical lower sections and change direction in the upper part.
In the lower levels, the steel columns are spaced at 6m centres around the edge beam, minimising slab edge deflection. The concrete perimeter columns are spaced at 3m, with loads transferred from concrete to steel columns by Vierendeel trusses (frames with fixed joints) at levels 36-40. The steel columns in the spire are spaced at 1.5m, again with transfer structures to distribute the loads.
Constructing the steel frame for the viewing gallery (levels 68-72) and spire presented a challenge. The floor plate was too small to allow layout space for materials and equipment, and the top structure is 66m high. Prefabricated modular construction was used, with each module designed to the maximum size that transportable by road (3m wide) and part-assembled on the ground to the lift limit of the tower crane (7.5 tonnes) before being raised into place.
Trial assembly of the spire frame was carried out at the steel fabricator’s yard, proving the modules could be erected rapidly and safely. On site, the spire was constructed using a tower crane cantilevered from a bracket on the exterior at level 54 (the mast that stabilises the spire would have obstructed the core crane). The last piece of the frame was lifted into position to top out the structure on 30th March 2012.
The length of the tower crane’s jib made it the UK’s tallest crane — 317m above street level. Getting it to site was complicated. The core crane erected the tower crane (September 2011), which then dismantled the core crane. Once the spire was complete, a recovery crane mounted at level 72 removed the tower crane. The recovery crane was then removed by a small spider crane, which was taken up piecemeal by jump lift, assembled, used and dismantled and returned to ground level by jump lift.
The building's eight inclined glass façades (the "shards") are divided into 18 facets, consisting of large angled planes of single glazing separated by narrow slots that provide natural ventilation to three 'garden' spaces on the office levels. Behind the glazing is a curtain wall of double-glazed units. The fragmented extra-white glass of the outer cladding reflects the changing light in unpredictable ways. It comprises 11,000 panes covering 56,000 sq m.
The cavity between the skins also conceals the Vierendeel truss structures. Solar gain is reduced automatically by the building maintenance system, which lowers blinds within the cavity as required. The exterior is cleaned via maintenance units in the plant rooms, which can deploy cradles to all areas.
The lateral forces acting on the structure and façades were determined by wind tunnel testing a 1:400 scale model. A more detailed model of the spire was also tested and further studies provided data on the wind environment at street level. The top of the Shard can move 300-400mm in the wind, with gusts of up to 161kph (100mph) recorded at the spire.
The building has an efficient combined heat and power plant, which runs on natural gas from the National Grid. Gas is converted into electricity, and heat recovered from the generator provides hot water for the building's domestic supply.
On 5th July 2012, the Shard was officially inaugurated by Sheikh Hamad bin Jassim bin Jaber al Thani (b.1959), Prime Minister and Minister of Foreign Affairs of Qatar, and the Duke of York. This marked the completion of the building's exterior, which was illuminated by 12 lasers and 30 searchlights, in time for the London Olympic Games (25th July to 12th August).
Practical completion was achieved in November 2012. On 1st February 2013, the observation gallery was opened to the public by the Mayor of London, Boris Johnson (b.1964). In November 2013, Queen Elizabeth II and the Duke of Edinburgh visited the building.
The Shard has a gross internal area of 127,000 sq m (net 85,000 sq m) and contains 54,000 cu m of concrete, 12,500 tonnes of structural steel and 320km of wiring.
Architect: Renzo Piano Building Workshop
Architect of record: Adamson Associates
Consulting architect (planning phase): Broadway Malyon
Structural and services engineer (planning phase): Arup
Vertical transportation (planning phase): Lerch, Bates & Associates
Structural engineer: WSP Cantor Seinuk
Services engineer: Arup
Vertical transportation: Lerch, Bates & Associates
Contractor: Mace
Landscape architect: Townshend Architects
London Bridge Station executive architect: Pascall+Watson
Research: ECPK
"Engineering The Shard, London: tallest building in western Europe" by John Parker, Civil Engineering, Vol.166, Issue 2, pp.66-73, London, May 2013
"Building the Shard" by John Parker, Ingenia, Issue 52, London, September 2012

The Shard