Research On Seismic Performance Of Reinforced Concrete Columns Under Biaxial Cyclic Loading

Many structual damage investigations afterearthquake and lots of shaking table tests show that biaxial lateral displacement is the most common seismic response for reinforced concrete frame structures.Structure vibration recorded aftershock monitoring & in shaking table test indicate that the seismic story drifts path of RC structure exhibit approximate ellipse,diagonal line and other irregular shapes,the biaxial displacement response of structures subjected to earthquake is universal and irregular.Studies have shown that under biaxial loading the RC column aseismic performance in the two horizontal directions have coupling effect: Damage in one direction will significantly reduce the seismic capacity of the other direction;the seismic capacity of the column will decrease significantly in both directions.However,at present biaxial seismic performance of RC columns is not adequately considered in structural design and seismic assessment.Further study is still needed.Therefor,9 horizontal biaxial pseudo static tests of RC cantilever columns and finite element simulation analysis of 60 RC cantilever columnswere are carried out.Mechanical properties such as bearing capacity,ultimate displacement,volume stirrup ratio,longitudinal reinforcement ratio and loading paths of columns were investigated.The main contents of this thesis are as follows:1)According to the section size 450 mm x450mm,height 4.2m and scale ratio 1:1.5,9 RC cantilever columns with shear span ratio of 3.8 are designed and constructed.Biaxial pseudo static test were carried out to investigate the effects of axial compression ratio,volume stirrup ratio,longitudinal reinforcement ratio and loading paths on the mechanical properties of columns.The force-displacement hysteresis curve,the skeleton curve,the strength degeneration curve,the stiffness degeneration curve and the viscous damping coefficient curve of the columns are obtained.The characteristics of mechanical properties such as stress mechanism,bearing capacity,ductility and ultimate drift of the columns under biaxial loading are analyzed.2)Mechanical performance of the specimens was simulated by OpenSEES,the calculation results are checked with experimental results to validate the analysis parameters.Then biaxial hysteretic analysis of 60 RC cantilever column were carried out,the effects of axial compression ratio,volume stirrup ratio,longitudinal reinforcement ratio and biaxial loading paths on the mechanical properties of columns were investigated.3)Based on experimental results and numerical analysis,the influence of biaxial loading paths on seismic behavior of reinforced concrete columns is analyzed;the adaptive biaxial loading path for ultimate displacement assessment are recommended.4)Based on the recommended loading path,the ultimate drift of both the experimental columns and the numerical simulation columns are compared with the value given by the main seismic codes at home and abroad.The appropriate ultimate drift angle for bi-diredcitonal RC frame structures are disccused.Then recommendation to seismic design and analysis of RC frame columns under biaxial seismic action are proposed according to the experiment and analysis results.