Calculation Model for Progressive Collapse Resistance of RC Beam-Column Assemblies Under Arbitrary Restraint Stiffness

Research on the whole-process mechanical behaviour of structural resistance to progressive collapse is the key of proposing an effective practical engineering design method. However, most of the existing theoretical studies on the progressive collapse of reinforced concrete (RC) frame only focused on a double-span beam-column assembly in the case of fixed end restraint. For the case of non-fixed end restraint, research on the progressive collapse resistance of the assembly was extremely limited. Based on the alternative load path (ALP) method, a RC beam-column assembly under arbitrary restraint stiffness was chosen as the object to propose an explicit calculation model of a double-span beam under concentrated load in this paper. On the basis of analysing the mechanism of progressive collapse, the calculation formulas for the bearing capacity-displacement of the assembly in the beam action (BA) mechanism stage, compressive arching action (CAA) mechanism stage and catenary action (CA) mechanism stage were derived in detail. In this calculation model, the influence of constraint conditions and beam-span ratio on the progressive collapse behaviour of the assembly could be emphatically considered. Finally, calculations were performed for progressive collapse tests for differences in restraint stiffness and the calculations were compared with the test results. Results demonstrated that the proposed calculation model could accurately predict the progressive collapse resistance of RC beam-column assemblies under arbitrary restraint stiffness.