PROGRESSIVE COLLAPSE ANALYSIS AND MECHANISM STUDY FOR LARGE-SPAN STEEL TRUSS STRUCTURES

Initial failure of local elements caused by accidental events may become a starting point of progressive collapse.Diferring from moment frames or bearing wall systems,the truss system widely used in public architectures with large-span is of low redundancy in nature.In order to raise its structural robustness,precise analysis and therefore valid design trategy shall be expected.As a case study,a steel truss roof is deeply investigated in this paper by numerical method,and the internal force redistribution after intial failure,dynamic effect and primay failure modes are studied.By post-intinial failure analysis,it is found there are three kinds of redistributary mechanisms for truss structure:rotation pin mechanism,sliding surface mechanism and long column mechanism.The concept of sensitive element and key element is conceived according to simplified mathematic models,which provides a simple measure to evulate the safety performance for such structural system.