Research On Collapse-resistance Behavior Of Reinforced Concrete Frame With Specially Shaped Columns

The RC frame structure with specially shaped columns is widely used in field of engineering for the favorable service function.But few literature paid attention to its progressive collapse potential.Thus,experimental research and theoretical analysis on the frame with specially shaped columns subjected to the loss of a ground corner column are investigated to further study the collapse-resistance performance and failure mechanism in the collapse process.The detailed work of this paper is stated as follows:In the dynamic test,the removal of the ground corner column had little effect on the global deformation of the structure and the structure after the test almost maintained in the elastic state.In the quasi static test,the collapse process consisted of four distinct stages: elastic stage,elasto-plastic stage,plastic-hinge stage,and collapse stage.During the experiment,the frame sustained loads primarily depending on the beam resisting mechanism.The simulated curves of the finite element analysis are validated in good agreement with those of the test.The specially shaped column frame and rectangular column frame are respectively analyzed to compare collapse-resistance performance.The results reveal that the specially shaped column frame has a slightly greater dynamic response in the nonlinear dynamic analysis.In the nonlinear static analysis,the stiffness of the rectangular column frame increases a little,while the collapse-resistance capacity remains nearly unchanged,indicating there is no obvious difference on collapse-resistance performance between the two frames.A simplified mechanical model to estimate the collapse-resistance capacity of the frame is established and the analytical expressions are derived.The beams in the failed bays are selected as analysis object for simplicity.The effects of the arch action and lateral rigidity of specially shaped columns are also considered.By the utilization of the simplified approach,the collapse-resistance capacity of the frame in the quasi static test could be estimated accurately.It is indicated from the nonlinear dynamic analysis on a six-storey frame with specially shaped columns that the model under any condition would not collapse.The redistribution of internal force mainly concentrates in the adjoining components with little influence on other members.It is indicated from the pushdown analysis that the collapse-resistance capacity increase with the decreasing of the storey on which the failure column locates.In the same storey,the frame in the short side column failure scenario has the best collapse-resistance capacity.The combination of the nonlinear dynamic analysis and pushdown analysis is employed to estimate the indicator of structural robustness of frames with specially shaped columns in different seismic grades.It is revealed that the frame designed in a high seismic grade has better robustness,which verifies the rationality of the method to evaluate the relative robustness of structures effectively.The weak columns all locate in the longitudinal side bay where the column grid is relatively sparse,which indicates the layout of the structure is related to the locations of the weak columns.