South Bank Tower
Updating the tired façade of the 30-storey tower on London’s South Bank was just the first stage of its transformation into a desirable mixed-use development. Both the tower and neighbouring podium have been raised in height, and new basements and an atrium constructed.
Raising the tower by eleven storeys meant detailed analysis of the existing structure and foundations. As the perimeter structural fins couldn’t take additional load, the new storeys cantilever from the core, which has spare load capacity and allowed it to be extended upwards. Wing walls and steel hangers support the majority of the new structure.
Three storeys were also added to the podium, constructed with a steel frame to minimise loads. Strengthening of the podium’s superstructure and foundations was required to accommodate the additional loads, while steel columns punch through existing concrete floors to take loads from the structural additions down to the foundations. The podium was also reconfigured to provide extra floor space. There were four cores along its length, separated by movement joints, and we sequenced a critical process to replace these with new perimeter cores and stitch the joints together.
We also constructed a two-storey basement under part of the site. Being close to the Thames, and extending below the water table, it posed a significant challenge to resist buoyancy forces. As it penetrates low-permeability London clay, we recommended incorporating a means of draining water from beneath the basement slab, reducing the need for tension piles to resist uplift.
Finite element analysis allowed us to model the ground underneath the site, examining different stages of construction and predicting ground movements and stresses placed on the Waterloo & City line, which runs underneath. The accuracy of this analysis allowed a reduction in the thickness of the basement walls, cutting construction costs and reducing the amount of temporary propping required during construction, while also maximising the amount of usable space.
Innovative upwards extension of an existing thirty-storey office tower in South London
£ 125 million
- 2016 UK Tekla BIM Award – Commercial Projects Winner
- 2016 Hermes Real Estate – RPI Award – Best Refurbishment Team
- 2016 IStructE Structural Award – Shortlisted
- 2015 NLA Award – Commendation for Conservation & Retrofit Category