Research On Restoring Force Behavior And Damage Model Of Reinforced Concrete Column With HRB600E High-strength Steel Bars

By now,few experimental studies has been done on the reinforced concrete columns with HRB600 E high-strength steel bars in China,which results in inconvenience in formulating the item on high-strength steel bars of Code for Design of Concrete Structures and promotion and application of high-strength steel bars.In this paper,the seismic performance of reinforced concrete columns with HRB600 E high-strength steel bars has been investigated through experimental studies and theoretical analysis.The results can provide experimental and theoretical basis for the revision of seismic code and the application of high-strength steel bars.Major research work and conclusions are as follows:10 high-strength reinforced concrete columns with different axial compression ratio,stirrup spacing,longitudinal reinforcement ratio and reinforcement strength have been tested under low cyclic loading.The restoring force behavior including the failure process,hysteresis curve,skeleton curve,displacement ductility,energy dissipation capacity,stiffness degradation and the strain law of the steel bar have been analyzed.The results show that: Bending failure occurs in all columns,with good plastic deformation and energy dissipation;HRB600E steel bars can fully exert tensile and compressive strength as longitudinal bars.When used as stirrups,they can better restrain the concrete in the core area.Moreover,with the increasing of axial compression ratio,the bearing capacity and energy dissipation of specimens increase while the stiffness degradation accelerates.Decreasing the stirrup spacing can significantly increase the peak loading and ductility,it also improves deformation and energy-dissipating capacity of specimens.When the longitudinal reinforcement ratio increases,the bearing capacity can be significantly increased,but ductility and energy-dissipating capacity reduce;In addition,with the replacement of steel bars with equal volume and equal strength,the bearing capacity of HRB600 E high-strength steel specimens increases,the stiffness degradation decelerates in the later stage,the plastic deformation capacity enhances,the seismic performance is more stable,and the energy-dissipating capacity and the ductility reduce but not obvious.The analysis of experimental data were regressed to achieve the skeleton curve model and rules of the artifacts and uninstall the stiffness degradation of hysteretic curve and reveal the hysteresis rules of the specimen under low cyclic loading.Base on this,a three-line restoring force model for rectangular concrete columns with HRB600 E high-strength steel bars was established.The calculated results of the restoring force model are in good agreement with the experimental results,which verifies the accuracy of the model.The damage index of each specimen has been calculated with representative modified Park-Ang damage model.It was found that the Chai model,Kunnath model,and Fu Jianping model can better evaluate the development law of damage index of high-strength reinforced concrete columns.A parameter correction has been carried out on the Wang Dongsheng model,Fu Guo model,and Chen Lin model according to the experiment data before failure.Based on the test data and related research results,a damage theoretical model was established,which can be applied to calculate the damage index of high-strength reinforced concrete columns.