Experimental study on progressive collapse behaviour of double-layer space truss (DLST) under sudden key member removal

Progressive collapse represents a critical safety concern for double-layer space truss (DLST) structures, which are widely used in large public buildings. This study investigates the progressive collapse behaviour of a four-point supported DLST structure through experimental and numerical investigations. An innovative experimental programme was developed to simulate initial member failures and monitor the subsequent structural behaviour in real time. Key members subjected to failure were comprehensively investigated, including the lower chord member at mid-span, the upper chord member at the support ends, and the diagonal web members at the supports. Test results show that the buckling of diagonal web members at the support end directly triggers progressive collapse, with the structure undergoing complete collapse in about 2.21 s. Internal force redistribution following member failure is analysed in detail, revealing distinct load-transfer mechanisms depending on the failed member. Three anti-collapse mechanisms namely arch action, catenary action, and beam action are identified throughout the collapse process. The global arch action dominates initially; after its disruption, a tensile path develops along the lower chord members, activating catenary and beam actions to resist collapse spread. Furthermore, while conventional finite element (FE) methods offered valid insights into force redistribution and anti-collapse mechanisms, advanced numerical methods are needed to accurately predict member fracture behaviour. The presented experimental framework and findings provide a benchmark for future research aimed at enhancing the robustness of DLST structures.