Collapse modelling analysis of a precast soft-storey building in Melbourne

Experimental field testing of a soft storey building in Melbourne has been undertaken by Swinburne University of Technology in collaboration with The University of Melbourne. The upper levels that consisted of precast walls and slabs were demolished to the first floor. The soft storey open ground floor was a precast concrete frame with connections significantly weaker than the members they connected. Four tests were conducted with combination between load directions (strong and weak) and restraints of ground slab (with or without ground slab). The experimental results show that soft storey columns were found to have significant displacement capacity irrespective of strength degradation. An analytical model has been developed to predict force-displacement relationship of the tested frame. The model includes the influences of: a) connection strength at column ends; b) gravity rocking strength; and c) ground slab restraint. Results from the developed model were found to be in excellent agreement with experimental test results, showing that the top connection in the form of an unbonded high strength steel bars dominated the overall load-deflection behaviour in the strong direction. However, the gravity rocking mechanism dominated the behaviour in the weak direction. The presence of the ground slab provides additional restraint to the column and significant additional lateral strength to the system.