“Orion played a pivotal role in ensuring we could manage project variations quickly, economically and accurately.”

Clive Lungley, PEP Associate Director

The challenge

Clapham One project, an £80m PPP scheme completed in September 2012, was commissioned by London Borough of Lambeth in order to create new public facilities, a leisure centre and luxury apartments as part of a wider regeneration of Clapham High Street.

In January 2010, established Hertfordshire business, PEP Civil & Structures Ltd, was appointed as the structural engineers for this landmark project, working with architect Studio Egret West and Joint Venture Developers, Cathedral Group & United House.

As part of this major redevelopment project the former Mary Seacole House office building on Clapham High Street was demolished and replaced with The Library Building; an award winning, iconic and sustainable building which is significant in both size and complexity. The Library Building comprises up to ten storeys of luxury residential apartments constructed over a three storey circular shaped public library, medical centre and a single storey basement car park. A focal point of the scheme at the lower level is a striking and innovative spiral ramp within the library, which rises three storeys and connects the medical centre, café, performance space, community rooms and other facilities. PEP’s brief was to deliver an economical design, therefore the need to value engineer the scheme to achieve the optimum solution was paramount, as was the necessity to provide fast and effective responses as the scheme evolved.

The solution

The engineering challengeThe Library Building was structurally very complex, as the architect’s exciting form threw up a number of interesting engineering challenges, including the extensive use of curved facades, complex load paths and transfer slabs resulting from differing structural grids, culminating in challenging foundation arrangements. However, as is often the case, the more complex the structure, the more beneficial software becomes and by taking advantage of the integrated building design approach with CSC’s Orion package, PEP was able handle the challenges quickly and with confidence. The library rampThe public library is situated on the northwest corner of the building with its signature oval ramp spiralling up from basement level to second floor, partially suspended from a 950mm thick transfer deck above. The architect’s original vision was for a column-free space however, with spans of up to 22m and the significant transfer loads from 10 storeys of apartments, the most effective and commercially acceptable solution was to incorporate eight columns around the inner perimeter of the ramp. PEP used Orion to investigate alternative solutions before settling on the final solution comprising five 1,200mm x 400mm rectangular columns and three 750mm diameter circular columns to the glazed main entrance off Clapham High Street.

Flat slab designWithin the residential apartments PEP

“It is clear that PEP continues to ‘punch above its weight’ and reap the benefits of its investment in CSC’s building design tools.”Barry Chapman, EMEA Director, CSC

Discover the benefits of Orion for yourselfVisit: www.cscworld.com

Fact file Name: PEP Civil & Structures Ltd

Location: Hertfordshire, UK

Incorporated: 1996

Key projects: Clapham One project, an

£80m PPP scheme commissioned by London

Borough of Lambeth in order to create new

public facilities, a leisure centre and luxury

apartments.

CSC products: Orion

Key benefits of Orion: PEP saved significant time and increased

productivity by managing eveolving project

variations from a single model.

adopted a 225mm thick reinforced concrete flat slab solution throughout. The footprint of residential apartments took a very different shape to the library below, resulting in the 10 storey apartments over-sailing the library significantly and a 950mm thick transfer deck required to carry the enormous loads. Away from the library, the remainder of the structure comprised seven storeys of apartments sitting above a single storey medical centre at ground level, with a single storey basement car park and plant rooms below. This mixed use nature of the building led to differing structural grids and column arrangement at each level thereby requiring PEP to design and detail a 425mm thick transfer slab at first floor and a 600mm thick transfer slab at ground floor.The challenge PEP faced for all the slabs was to achieve an economic solution by carefully balancing overall slab thickness versus reinforcement, acceptable deflection estimates, punching shear requirements and the ramifications on the foundations. Clive Lungley, PEP Associate Director, found that by using the Finite Element capability in Orion, he was able to iterate and optimise the slab design quickly to establish the most efficient solution. Load chase down and foundationsFaced with an awkward footprint, eccentric and discontinuous cores and many transfer levels, Orion’s unique Finite Element load chase-down was essential in helping quickly predict load paths and accurate foundation forces early in the process, thus enabling an economic foundation solution to be designed at tender stage.

The basement slab was optimised to be a 250mm thick suspended slab supported onto perimeter secant wall and internal bored piles; these were typically 400mm diameter but under heavily loaded areas such as the cores, the piles increased to 600mm diameter.

Prior to the demolition of Mary Seacole House, PEP established the location of existing foundations using as-built drawings and designed the new foundations to fit around these. However, due to inaccuracies in as-built drawings, during installation the piling contractor found over 100 piles in unexpected locations resulting in clashes with the new pile arrangements. With temporary halting of works, PEP were under considerable pressure to modify the design and reposition the new piles quickly, which was achieved with the integrated foundation capability within Orion. Originally the building height was kept below 30m to meet the agreed planning consent, however at a later stage commercial pressures resulted in the developer adding an additional two floors of luxury apartments which increased the overall building height to 36m. These were initially schemed in steel/timber to minimise ramifications on the already designed foundations, but ultimately the contractor opted to construct the apartments from concrete. The significant increase in weight resulting from this variation required PEP to carry out further checks on the design and with Orion they were able to establish quickly that the proposed foundations were still adequate for the additional loading but that the main transfer slab needed to be thickened by 50mm. Lateral stabilityWith a building of such irregular shape and stepped height, determining the lateral stability and twist was a complex task. Lateral stability was provided by three 200mm thick slip-formed RC cores; whilst two of these were full height from basement to roof level, the third

terminated on the 950mm thick transfer deck over the library, with the resulting lateral forces being transferred through the slab into walls below. Orion saved yet more time for PEP by fully automating the application of the notional horizontal loads in accordance with BS8110, as well as predicting the resultant drift and twist of the structure each and everytime modifications were required.

The result

Clive Lungley, PEP Associate Director, said: “PEP needed to react to major changes throughout the project, partly due to the problems encountered during piling but also because the scheme evolved continually. Orion played a pivotal role in ensuring we could manage the project variations from a single design model quickly, economically and accurately.

CSC software enables us to compete with the heavyweights of the industry with escalating success. The time savings we achieve and the gains in productivity and efficiency are impressive. We continue to reap the benefits of our investment in CSC’s building design tools”. CSC’s EMEA Director, Barry Chapman, said: “The Library Building at Clapham One is an exciting and prestigious project which has clearly provided many technical challenges to the design team. It’s gratifying to see our tools help a medium sized practice deliver such a large and complicated project by using the right software tools efficiently.”

Discover the benefits of Orion for yourselfVisit: www.cscworld.com