Analytical Model for Progressive Collapse of Multi-story RC Frame after a Ground-story Middle Column Removal
In a multi-story RC frame,when the ground-story middle column fails,the unbalanced load is borne by the stories above the failed columns,and the load-carrying capacity is significantly in-creased compared to a single-story frame.However,due to the lack of systematic experimental and nu-merical investigations on the progressive collapse resistance of spatial multi-story RC frames,the force mechanisms of the stories above the failed column for resisting progressive collapse are still un-clear.Moreover,there are few analytical models for quantifying the progressive collapse resistance of multi-story RC frame structures among existing studies.Therefore,9 typical multi-story RC frames are designed following the Chinese design codes and their progressive collapse behaviors under the ground-story middle column removal scenario are analyzed.The internal forces and strain develop-ments of the beams on each story are systematically analyzed.And the progressive collapse-resisting mechanisms of various stories in an RC frame are discussed.On this basis,the calculation model of single-story RC beam-column substructures is combined to establish the analytical model for quantify-ing the progressive collapse resistance of a multi-story RC frame after the ground-story middle column removal,by calculating the resistance contributions of different stories.The experimental tests and nu-merical simulations are compared with the calculated results to verify the accuracy of the proposed model.The results show that:(1)Following the removal of the column,significant compressive arch action and catenary action are observed in the ground story beams.(2)When components of varying di-mensions are arranged vertically within the RC frame,compressive arch action is observed in the low-er floor beams that experience a change in component size.(3)Apart from the aforementioned floors,beams on other floors generally exhibit progressive collapse resistance through flexural actions.(4)The proposed analytical model can provide a satisfying estimation of the progressive collapse resis-tance of a multi-story RC frame under the ground-story column removal scenario.
multi-story RC framesprogressive collapsenumerical simulationsstress mechanismcal-culation model