Study On Oblique Seismic Behavior Of High Strength Reinforced Concrete Columns

Reinforced concrete column is the most important load-bearing component in the frame structure.Its bearing capacity,ductility,energy consumption and other seismic performance are important factors affecting the seismic safety of the structure.The current seismic code of our country stipulates that the seismic design of frame structure should follow the principle of "strong column and weak beam".However,in recent years,many seismic disaster investigations have found that the plastic hinge appears at the column end of reinforced concrete frame structure before the beam end,resulting in the damage of building structure,which has not effectively formed the seismic design of "strong column and weak beam" required by the seismic code One of the important reasons for the calculation principle is that the current code only considers the bearing capacity checking calculation of two principal axis directions,and does not consider the multi-dimensional and arbitrary direction of seismic action.In the actual earthquake,any direction in the structure plane may become the most unfavorable direction of action.When the local vibration is input along the non principal axis direction of the structure,the frame column needs to bear the internal force generated by the earthquake action in the two principal axis directions,while the frame beam only needs to bear the internal force on its respective principal axis,and the existence of the floor slab has a certain strengthening effect on the beam strength,resulting in the oblique bearing capacity of the frame column unable to meet the requirements of "strong column weak beam".Therefore,further research is needed to ensure the seismic safety of reinforced concrete columns under the action of oblique earthquakes.In this paper,seven long concrete columns with high-strength steel bars were designed,and low-cycle reciprocating loading tests were carried out.The seismic direction of the reinforcedconcrete columns was analyzed with the loading direction and axial compression ratio as the main variables,and three types of column end restraint methods are proposed to study their effectiveness in improving the diagonal seismic performance of reinforced concrete columns.Based on the method of cross-section equivalence and the principle of balance,a simplified calculation method for the normal section flexural bearing capacity of oblique compression-bending members was proposed,and the correctness of the simplified calculation method was proved by comparison with the test results.Through the OpenSees finite element program,the nonlinear element model of the test specimen was established,and the accuracy of the nonlinear finite element model was verified by comparing with the experimental results.The main conclusions of this paper are as follows:(1)All specimens show the characteristics of bending failure and have better deformation capacity and energy dissipation performance.The concrete columns with high-strength reinforcement can still meet the seismic requirements under high axial compression ratio.(2)When the axial compression ratio is the same,the bearing capacity,deformation capacity and energy consumption capacity of inclined load specimen are lower than that of main shaft load specimen,but the degradation rate of stiffness is slower.With the increase of axial compression ratio,the bearing capacity and stiffness of the specimens are increased,but the decrease rate of bearing capacity is accelerated after peak load,the degradation trend of stiffness is accelerated,and the deformation capacity of the specimens becomes worse.(3)Steel mesh and carbon fiber cloth constraints have significant effects on improving the diagonal seismic performance of reinforced concrete columns under high axial compression ratio.Among them,the steel grid constraint can significantly improve the bearing capacity and initial stiffness of the specimen under oblique loading,and to a certain extent,it can slow down the decline rate of bearing capacity and the degradation trend of stiffness after peak load of the specimen,and effectively improve the deformation capacity and energy consumption capacity of the specimen.To a certain extent,the carbon fiber cloth constraint improves the bearing capacity of the test piece,and the most significant effect on the deformation capacity of the test piece is toslow down the degradation trend of the rigidity of the test piece,and greatly improve the energy consumption capacity.(4)The simplified calculation method of the normal section flexural bearing capacity of reinforced concrete oblique compression-bending members based on the principle of cross-section equivalence and the principle of balance has good correctness,and has a certain reference function for practical engineering.(5)Using OpenSees as a platform to establish a finite element model,by selecting appropriate material constitutive parameters,simulation results that are in good agreement with the test can be obtained,and the accuracy of the finite element model is verified.