Collapse modelling analysis of a precast soft storey building in Australia

A unique experimental field test study that provides insight into the push-over load–deflection and collapse behaviour of a soft storey building is reported in this paper. The five storey building had been identified as being particularly vulnerable to earthquake excitation due to the particularly weak connections at each end of the ground floor precast columns that constituted the soft storey. Consequently, four field tests were undertaken to investigate the actual lateral force–deflection behaviour of the soft storey columns. Interestingly, the tests indicated that the soft storey columns possessed significant displacement capacity despite significant strength degradation. An analytical model developed to predict the overall force–displacement relationship that was influenced by the three component mechanisms of (a) connection strength at column ends, (b) gravity rocking strength and (c) ground slab interaction, was found to be in excellent agreement with the experimental test results. The presence of the ‘non-structural’ ground slab provided additional lateral strength to the system and greatly influenced the ‘as-built’ performance. The displacement capacity of the precast soft storey system was much greater than an equivalent in situ system, due to the rigid body rocking behaviour of the columns. The precast soft storey system was found to have sufficient displacement capacity for lower seismic regions, but the performance was considered marginal for higher seismic regions.