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.
Innovative upwards extension of an existing thirty-storey office tower in South London
Raising the tower by eleven storeys meant detail wind and structural analysis of the existing structure and foundations. CFD wind analysis was used to determine the wind forces and maximise the capacity of additional floors while maintaining the human comfort levels at the ground plane. As the perimeter structural fins could not take additional load, the new storeys cantilever from the core, which had spare load capacity, allowing it to be extended upwards. Wing walls and steel hangers from the 31st floor support the majority of the new structure.
The linking of the tower and podium buildings through a glazed atrium was encouraged in the design process to mitigate the existing wind forces at ground level, creating an improved human comfort environment.
The podium has been reconfigured to provide extra floor space. With four cores along its length, separated by movement joints, we sequenced a critical process to replace these with new perimeter cores and stitch the joints together. Three storeys were also added above the podium, constructed with a steel frame to minimise loads. Strengthening of the podium’s superstructure and foundations was required to accommodate additional loads, and steel columns punch through the existing floors to take additional loads down to the foundations.
A two-storey basement has been constructed under part of the site, which posed a significant challenge due to the close proximity to the Thames. 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 also 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.
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