Strengthening the 1960s UK Commonwealth Institute hyperbolic paraboloid roof

Abstract

The Grade II*-listed 1960s roof to the former Commonwealth Institute consists of a central post-tensioned concrete hyperbolic paraboloid shell, typically only 75 mm thick, and is one of the few examples of large-scale concrete shell structures in the UK. After being unoccupied for a decade, in 2012, the Design Museum announced its plans to move into and redevelop the building. In order to make the space functional, the interior and foundations needed to be demolished and the entire 3100 m2, 2000 t roof held up 20 m above ground temporarily while the new structure was constructed underneath. This paper explores in detail the steps taken to assess the relatively delicate existing roof structure for the change in loading and future movements in both the temporary and permanent conditions and the resulting innovative strengthening, repair and temporary works required. Limited historical drawings and papers were available, and therefore, non-destructive testing and careful intrusive investigations were used to obtain more information on the as-built details. In order to determine the structural behaviour, hand calculations were conducted to back-calculate the original design intent, and computer modelling was used to conduct sensitivity analyses of the load paths.