Collapse Failure Modes Of Reinforced Concrete Columns And Regressive Displacement Blocking Structure Experiment Research

Research on the collapse mechanism and collapse mode of reinforced concrete（RC）frame columns under strong earthquakes is one of the hotspots in the study of building structure collapse resistance.Based on the existing research results and seismic damage data of RC frame columns,this paper summarizes five possible collapse failure modes of RC frame columns from the perspective of structural collapse: modes a,b,c,d and e.Among them,mode a: the overall overturning failure caused by the fracture of the column bottom longitudinal reinforcement or the bonding failure.Mode b: The shear cracks at both ends of the column bottom section constantly "eroded" toward the neutral axis of the section,causing the column to collapse vertically.c: Sheartension cracks and shear-compression cracks penetrate through the bottom section of the column,causing collapse and failure caused by bending and shear failure.d: Shear-tension cracks develop to the edge of the cross-section compression zone before shear-compression cracks occur,resulting in overall shear-tension failure of the column.Mode e: Shear cracks will fail the oblique pressure damage caused by the oblique splitting of the cylinder.Among them,modes a and e occur in frame columns with poorly arranged steel bars and short columns with large axial compression ratios,respectively,and do not meet the seismic design specifications of RC frame columns,especially the bottom RC frame columns.In order to further distinguish the other three common collapse failure modes,this paper uses the Mohr-Coulomb failure criterion of tensile fracture,combined with the stress distribution law of RC frame columns under compression and shear,through the axial compression ratio and the aspect ratio（shear span ratio）In order to influence the parameters,the occurrence conditions and scope of these three collapse failure modes are divided,and the above three collapse failure modes are verified through literature test specimens.With the rapid development of computer technology,numerical simulation analysis is a useful supplement to structural test analysis.In order to further verify the collapse failure modes of RC frame columns summarized above,this paper uses Ansys finite element simulation software to establish six finite element models of RC frame columns with different axial compression ratios and aspect ratios,using element "life and death" technology With the restart analysis method,the development of the shear failure zone and shear crack zone at the end of the RC frame column under different working conditions are analyzed,and the failure modes of the column end of the six finite element models and the three theoretical collapses are obtained.The failure mode is in good agreement,and it is further known that the best ductility is collapsed failure mode b.In the actual RC frame structure anti-collapse design,in order to prevent the above-mentioned collapse failure of the RC frame structure column,this paper designs and produces a displacementretracting frame anti-collapse barrier structure,which provides a certain degree of resistance for the frame column under the action of seismic force.Lateral and vertical support.Through a comparative test composed of two full-scale assembled RC frames,the seismic performance of all aspects of the frame without or with this blocking structure is comprehensively analyzed.The research shows that the displacement-retracting anti-collapse barrier structure can better restrain the further development of cracks before and after the structure enters the yielding state,and reduce the side displacement of the frame.From the hysteresis curve and skeleton curve of the structure,it can be seen that the barrier structure can better enable the structure to withstand greater seismic force.From the stiffness degradation curve,it can be seen that when the barrier structure enters work,the stiffness of the overall structure can be increased.It can be seen from the force-strain curve of the reinforcement that the barrier structure can slow down the increase in the strain of the column end longitudinal reinforcement,that is,the seismic energy concentrated at the column end can be "shared" to other areas of the column,thereby effectively preventing the column Prematurely enter the collapsed failure state.