The complex structure of The Shard tower at the London Bridge quarter presented multiple design challenges. WSP used Bentley’s structural software to optimise unique geometric design of the tower while saving time and construction cost.
Soaring 95 stories above the South Bank of the Thames, The Shard at London Bridge Quarter is the tallest building in Western Europe. As its name suggests, the building is comprised of multiple glass shards that merge to form an elongated pyramid, creating a complex structural form with many design challenges. The skyscraper was also designed for sustainability, using recycled construction materials and targeting an ‘Excellent’ BREEAM rating. The developer, Sellar Property Group chose WSP, a global design, engineering, and management consultancy to deliver a technical solution for The Shard. Using Bentley’s RAM structural analysis and design software products, WSP reduced steelwork frame tonnage from 200 kg per sq metre to 100 kg per sq metre.
The slender, 1,016-foot pyramid is a multi-use, vertical city with commercial offices, international restaurants, a five-star Shangri-La hotel, exclusive residences, and public viewing attraction. With a location adjacent to the London Bridge multi-transit station, which averages more than 54 million commuters per year, The Shard was conceived as a way to advance the British government’s push for high-density development at transit nodes. Italian architect Renzo Piano was appointed to design the 1.2-million-square-foot skyscraper as an “expression of the energy” of central London and design of the $729-million (shell and core) skyscraper began in 2000.
WSP, which has a strong history of structural design work on signature skyscrapers such as the 1,776-foot Freedom Tower in New York City, was retained initially in 2003 for peer review and value engineering for a schema developed by another engineer. “We basically won the confidence of Sellar when we did that review. We were able to demonstrate that we could save on the structural costs,” ,” says Rodolfo Giannini, Technical Director and Shard Chief Project Engineer at WSP. The company used Bentley’s RAM structural analysis and design software products to meet design goals for maximum space, minimum construction cost, and optimum safety on this project.
Multiple design challenges
The multi-use nature of The Shard posed one of the greater challenges for the design teams. While the space within high-rise buildings typically serves one primary function, The Shard’s 72 habitable floors form a diverse vertical city.
The architect’s plan designated floors 4 through 28 for offices, 31 through 33 for restaurants, 34 through 52 for a 200-room hotel, 53 through 65 for residences, and 68 through 72 for a viewing gallery. WSP’s challenge was to reconcile the need for entirely different floor framing systems necessary for the residential and office floors.
The non-repetitive nature of the floor plan geometry posed another serious challenge for WSP’s designers. While many high-rise buildings derive their exterior geometry from a mathematical equation, or vary in an easily predictable manner along the height, this was not the case with The Shard, which is comprised of an array of glass shards that merge to form an elongated pyramid, with little vertical geometric continuity. “Each floor plan is different, but in a different way,” explains Giannini. “This kind of random geometry was the most challenging aspect because it dictated where everything else was placed: where columns needed to be discontinued and where transfer conditions were needed.”
To meet the design goals for this radical structural form, WSP devised a hybrid approach that stacked a series of different floor framing systems on top of each other. Composite steel floors were used for the office floors and the public spaces at the lowest levels of the hotel, while post-tensioned concrete floors were used for the hotel guest rooms and residences. Finally, a steelwork spire with a public viewing gallery comprised the highest extent of the structure. The design provided a high-level of structural robustness, with a number of safety-related innovations, including state-of-the-art blast protection and structural fire engineering design. The unusual layering of concrete levels on top of steel levels also had beneficial dynamic effects on the structure. Due to the additional mass and stiffness of the concrete-framed levels, the expected lateral acceleration due to wind significantly reduced sway at residential levels.
WSP also achieved goals beyond the design of the fundamental structural system, including exceptional environmental credentials. Using sustainable materials and meeting zero waste requirements, there was no overdesign allowed. WSP worked together with the wider design team, including associate architect Adamson Associates and mechanical, electrical, and plumbing (MEP) engineer Arup, to achieve maximum floor area and minimum structure. For instance, the schema done by the original engineer had 200 kg per square metre of steelwork frame. WSP reduced this by half to 100 kg per sq metre through multiple design iterations and optimisations. Sustainability was also addressed by using steel with a recycled content of approximately 55%.
RAM for design optimisation
Choosing the right structural design software was simple for WSP. “When we have a steel frame, we use Bentley’s RAM Structural System by default. When we have a reinforced or post-tensioned concrete frame, we use RAM Concept,” says Giannini. “This software is our natural choice as it automates our most time-consuming design tasks and produces the most efficient designs.”
The Shard commercial office space floors required a distribution zone below the ceiling for services, as well as open floor space. The ideal material for this requirement was composite steel beams supporting a concrete slab. WSP used RAM Structural System to design the composite steel floor framing for the offices and portion of the hotel between levels 3 and 40, reducing the steel tonnage to half of what it was in the original schema. RAM’s steel beam auto-design capabilities and third-party cellular beam plug-in allowed WSP to evaluate various framing alternatives and identify the superior option. The software’s characteristic method of distributing gravity loads over the entire structure with utmost precision, followed by member optimisation to an exhaustive list of strength, serviceability, and code requirements, resulted in a design in which each element supported the exact load assigned to it, without any excess material.
“That’s where the RAM Structural System is helpful, because it performs the optimisation process that would take ages for us to do by hand, beam by beam,” emphasises Giannini while adding that changes could be accommodated and the floor redesigned and accuracies checked in a matter of minutes, not hours or days.
RAM Concept was also used in multiple capacities on The Shard project. The entire building is founded on a concrete raft supported by 50-meter deep piles. RAM Concept’s mats module was used to assess the stability of the raft system under the loads introduced by the superstructure, determine the required thickness of the mat, and identify the required steel reinforcing. RAM Concept’s post-tension design capabilities were used not only in selecting the post-tensioning configuration and conventional reinforcing, but also in determining at which level the transition from a steel-framed floor to a post-tensioned floor should occur. Considering the building’s tapered geometry, WSP determined that level 41 was the optimum location to switch from steel to post-tensioned floors. RAM Concept calculations showed that beginning with level 41, the 200 mm slab could span from the perimetre columns to the center core for the desired open floor plan without requiring intermediate columns.
Achieving the optimal design solution required multiple iterations of the structural models — a process that was simplified through the use of the Bentley software. “Every model that we did, we did at least 10 times, and not because we were inefficient,” points out Giannini. WSP dealt with changes from the architect, client, services engineer, and even changes in the predicted structural loads. Design wind loads were revised after wind tunnel test results warranted changes, which resulted in adjustments to the structural system for lateral stability.
Analysis and design of The Shard’s raft foundation in RAM Concept.
RAM Concept view of tendon system at level 41
RoI on RAM
The RAM Structural System and RAM Concept are embedded in WSP’s way of working. “As soon as there is a new building or a new project, we know ‘this part is with RAM Concept, that part is with RAM Structural System’,” says Giannini, adding that every WSP engineer knows how to use these two applications, and how to push them to their limits to achieve efficiency in design.
WSP cites the user-friendliness of RAM Structural System and RAM Concept as the primary appeal of the software. On The Shard project, where the design phase lasted nearly five years, there was a constant change of engineers on the job but because of RAM software’s ease of use, new engineers were able to immediately start where their predecessors had left off. The software also streamlined workflows, avoided duplication in manual tasks, and improved data and design quality.
Given The Shard’s unique blend of irregular geometry, multi-use occupancies, and dual materials, optimisation of the structural design using the RAM product line produced valuable savings. Construction of The Shard commenced in 2009 and it was formally inaugurated on July 5, 2012.