Situated in midtown, on the eastern edge of the City of Westminster, the 44,000 sq ft island site of 48 Carey Street is surrounded by institutional buildings such as the Royal Courts of Justice, the Royal College of Surgeons and the London School of Economics. The existing seven- storey building was demolished to the basement slab, retaining existing basement walls, and replaced with a new nine-storey prime residential building with a further double basement level.
Key technical challenges
The building height is limited by planning considerations. To achieve a viable scheme at nine levels, the floor slabs (spanning up to 8.0m) are restricted to 200mm thick. Post-tensioning is used with careful integration of anchorages, façade fixings and thermal isolation hardware. The slabs also support stone-faced cladding in line with the surrounding buildings.
The building plan (80m x 60m) is arranged around a central courtyard, has no movement joints, and uses a pour-strip approach to limit shrinkage stresses and relieve restraint from opposing cores during post-tensioning. Differential movements were consideration for casting the pour joints and installing the cladding across the four blocks.
To simplify basement construction and minimize temporary works, the existing upper-basement walls are retained, and the lower basement constructed using secant walls installed within the existing basement zone.
A raft slab is founded within the London clay and designed for residual differential heave pressures resulting from the phased build, in addition to gravity loads.
RBG carried out analysis to determine the locked-in stresses and differential settlements for the proposed construction methodology and sequencing, which entailed the building being constructed in two halves.
RBG Value Add
- Detailed Analysis carried out by Construction Engineering Team to allow building to be constructed in two halves speeding up programme.
- Introduction of PT slabs to reduce building height
- Complex terraced transfer systems, various solutions including transfer slabs, walking columns and transfer beams. Coordination with architectural internal room layouts was challenging.
- Tower crane integration with the raft slab and phased block construction.
GBP £135 million
9-storeys with double level basement
Robert Bird Group Services:
Code for Sustainable Homes Level 4