Capella Laboratory, Cambridge

Capella is a new, seven-storey bioscience laboratory built at the world-famous Addenbrookes Hospital site, at Cambridge University. The project brief demanded a low response factor – in layman’s terms, low floor vibration.

Normally, a low response factor is achieved through a rigid cast-in-situ concrete structure. Preliminary designs specified an overall floor depth of 700 mm. However, it was quickly realised that this solution raised a number of difficulties, including a local shortage of ready-mixed concrete supply, plus the amount of labour and construction plant required. Increased traffic, noise and disruption would also have caused serious problems in the already congested hospital area.

During the tender period, main contractor Kier Group requested that PCE Ltd., a specialist structural frame contractor, consider solutions resulting in a faster build program, with reduced on-site activity, less in-situ concrete and a more eco-friendly impact.

Already familiar with the DELTABEAM® Slim Floor Structure, PCE asked IPHA members, Peikko, if they could be used in combination with hollowcore slabs and a structural topping. The key question – could the low response factor be achieved with slimmer floors?

A project with good vibes…

Initial calculations carried out by Peikko indicated that the vibration requirements could be met, whilst still gaining the construction advantages offered by this alternative solution. Further design work was then approved by consultants and vibration specialists. Finally, a detailed FEM (Finite Element Analysis) revealed that the specification could be achieved with D32-500 DELTABEAM®s, 300 mm deep hollowcore slabs, and 200mm of structural concrete topping.

The resulting hybrid frame combines the benefits of both precast, and cast-in-situ techniques. Prestressed hollowcore slabs for the project were supplied by another IPHA member, FP McCann. A vibration test, undertaken on floors after construction, proved compliance between the theoretical design and eventual solution.

According to estimates, this construction method has reduced the dead weight of the building by more than 3,000 tons, and resulted in over 500 fewer vehicle deliveries to site, when compared with original designs. Furthermore, the construction program was 20 weeks faster, and saved more than 2,500 man-weeks. Finally, as hoped, the overall carbon footprint of the project was significantly reduced.