BAM’s challenge was to bring this six-decade old building up to modern standards, and effectively double its usable floor area. This involved a range of works, some of them very visible and others hidden away in the heart of the building.
On top of new foundations and a new basement slab, BAM created a reinforced concrete core and structure for the retained elements. The six extra floors were then added around a steel structure. In addition, a side extension has created an extra four floors in some areas, and five in others.
This ambitious scheme involved some major technical challenges – many of them impossible to foresee until BAM was actually on site – but the team used extensive BIM360 modelling and creative engineering solutions to overcome them.
One of the key techniques used was a façade retention approach. To facilitate the new extension on top of the building, the existing façade was restrained by an external steel frame, while the inside of the building was cut away. A new concrete structure was then built to the lower storeys and a new steel structure was created to support the additional six levels on top.
This connection detail was discussed at length between BAM, Robert Bird Group, Frasers Property UK and the subcontractors: initially as hand-drawn sketches and 2D models, and finally as a full 3D model of all interfacing elements. Completing this process early in the project was vital in mitigating risk at later stages.
An intricate 4D model of the piling methodology and sequencing was another innovation that added significant value on the project.