Chips

Chips is a large new building for Urban Splash, part of the regeneration of East Manchester. It was designed by SMC Alsop and Martin Stockley Associates, and built by Urban Splash Build. Its nine storeys contain 142 apartments over commercial space at ground level, with a basement containing car parking and plant under the whole building. The site is narrow, with canals on three sides. The frame is of reinforced concrete with exposed flat slabs supported on an irregular column grid, which responds to the offsetting of storeys in the long elevations. What makes this building unusual, and a particular challenge for the structural engineer, is the requirement to cantilever the six upper floors over the end of the building. Cantilevers seem to be one of the current architectural fashions, and they can be achieved without too much difficulty with a steel frame. But Chips has a concrete frame and the cantilever is large. The middle three floors cantilever 13.5 metres, and the upper three floors about 8 metres. Such large cantilevers create very considerable problems of providing a back span and controlling deflections and in doing it without blowing the budget. Martin Stockley have managed this difficult task by a rigorous analysis of how the deflections would increase during construction. The sequence of construction and temporary propping were worked out with the builder. Creep deflections were very carefully analysed and were partly controlled by inserting steelwork within the reinforcement and by a specially designed concrete mix. Measurements taken as the construction proceeded confirmed that the actual deflections were as predicted.