Shear Strength Degradation And Failure Modes Of Steel Reinforced High-Strength Concrete Columns

The SRHC(Steel Reinforced High Strength Concrete)columns offer benefits such as high load-bearing capacity,significant stiffness,and excellent resistance to earthquakes.However,due to the high brittleness of high-strength concrete,in cases where the design is not reasonable,SRHC columns may experience unexpected low ductility shear(bendingshear or shear)failure during strong earthquakes,leading to local or overall collapse of bridge structures.Currently,there is limited research both domestically and internationally on the shear failure,shear carrying capacity degradation,and influencing factors of SRHC columns.Based on existing research results,it is currently impossible to judge the failure mode of SRHC columns under earthquake action and avoid low ductility shear failure in design.Therefore,this paper conducted pseudo-static tests and numerical simulations on SRHC columns to study the failure mode of SRHC columns under different design parameters,the proportion of each deformation component,and influencing factors.Based on this,a formula for the shear carrying capacity degradation of SRHC columns and a method for identifying the failure mode of SRHC columns have been proposed.The main research content is as follows:(1)Design and complete pseudo-static tests on four SRHC columns.Based on the test results,the impact of each design parameter on the failure process,failure modes,hysteresis performance,skeleton curves,and displacement ductility were analyzed.The results showed that when the columns is under appropriate reinforcement arrangement and has an axial compression ratio of 0.25,SRHC columns had good deformation capacity and shear resistance under cyclic loads,exhibiting low ductility bending failure.Conversely,when the axial compression ratio was 0.38 and the reinforcement configuration was unreasonable,the ductility was low,and bending-shear failure occurred.(2)Based on the ABAQUS finite element analysis software,a refined modeling of SRHC columns is performed,considering various aspects such as material constitutive selection,element type selection,meshing,interactions,boundary conditions,analysis step settings,and loading methods.The finite element calculations are compared with the hysteresis curve and skeleton curve obtained from experimental measurements.The two curves show good agreement and overall consistent variations.The displacement ductility factor is compared with the ultimate elastic-plastic displacement angle,and the difference between them is small and within a controllable range,thus validating the accuracy of the modeling method.(3)Based on the validated finite element modeling method,a parametric analysis of SRHC columns is conducted to investigate the influence of shear-span ratio,axial load ratio,and reinforcement ratio on the hysteresis performance,skeleton curve,and deformation components of SRHC columns.By analyzing the displacement changes at different heights along the column height direction during the loading process,the variation patterns of bending deformation and shear deformation components in the SRHC column,their proportions to the total deformation at the column end,as well as the influence of shear-span ratio,axial load ratio,and reinforcement ratio on the proportion of bending deformation to the total deformation at the column end are studied.The research indicates that the numerical simulated specimens experience three failure modes: bending failure,bending-shear failure,and shear failure.Both the bending deformation component and shear deformation component increase with the increase of total deformation at the column end.In specimens that undergo bending failure,the bending deformation accounts for 80% to 90% of the total deformation at the column end,while in specimens that undergo bending-shear failure,the bending deformation accounts for 75% to 90% of the total deformation at the column end.