The Crossing is a new $140 million retail development in the city of Christchurch that forms part of the post-earthquake city redevelopment. It will feature 14,000 m² of retail and hospitality space, 5,000 m² of commercial space and a purpose built eight storey carpark building for 630 cars.
The eight storey carpark building is proposed to be constructed of structural steel framing, featuring long span steel beams supporting a composite floor beam. The New Zealand Building Code requires the steel framing to be protected with passive fire protection. The application of passive fire protection would impose capital installation costs and also long term maintenance costs.
Holmes Fire was engaged to investigate if the passive fire protection requirements could be safely rationalised. Holmes Fire undertook a series of advanced analyses using non-linear finite element analysis to analyse the stability of the carpark structure in fire conditions, without passive fire protection to all the beams. The analysis considered the behaviour of the structural frame under exposure to fully developed realistic vehicle fires.
The analysis was able to consider the complex three-dimensional spatial variation of temperature within the structure. The analysis showed that the frame, without passive fire protection, could resist the effects of fire and maintained its structural stability through load redistribution and tensile membrane action.
The resulting analysis enabled all the beams, with a total length in excess of 6,000 m, to be unprotected. This provided significant capital cost savings and ongoing maintenance of the passive fire protection.