Research On Seismic Performance Of 600MPa Grade Reinforced Concrete Columns

By now,few studies have been done on the seismic behavior of RC columns with grade 600 MPa steel bars,which results in inconvenience in revis ing the item on high shrength steel bars and application of high steel bars in projects.In this paper,the seismic behavior of RC columns with grade 600 MPa steel bars is investigated through analisys,experimental studies in order to provide theoretical and experimental bases for the revising of code GB50010 as well as the application of grade 600 MPa steel bars in projects.(1)Six RC columns with shear span ratio of 3.2 were tested under the low-cyclic reversed loading,including five specimens reinforced with grade 600 MPa steel bars and one specimen with grade 600 MPa steel bars for comparison.Further more,various factors of seismic behaviour were analyzed including the strength of steel bar,stirrup spacing and axial compression ratio on failure modes,hysteretic hoops,skeleton curves,bearing capacity and ductility,dissipation capacity,degradation of stiffness and strength,and accumulated damage.As is shown in the erperiments that the bending failure is the main patterns of specimens and the bearing capacity and energy dissipation of specimens increased with the improvement of steel bar strength.What is more,the accumulated damage of specimens was slow down while the ductility of specimens was decreased.Increasing the stirrup spacing could significantly decrease the ductility and energy-dissipating capacity of specimens,it will also accelerate the strength degradation and damage accumulation of specimens in the late loading.However,there was no effect on bearing capacity of specimens.Last but not least,when the axial compression ratio was between 0.2 and 0.5,the bearing capacity and the energy dissipation energy of the specimen can be obviously improved as is the axial compression ratio increased.However,the fracture of longitudinal bars were observed,resulting in accelerated stiffness degradation and strength attenuation of specimens in the later stage,and reducing the deformation capacity.(2)Base on the theoretical analys is and experimental data regression,this paper presents restoring force model of concrete column with grade 600 MPa steel bars.Empirical formulas of characteristic parameters such as the yield load,displacement of yield peak,peak load,displacment of the peak load in skeleton curve are put forward.At the same time,the analysis of test data were regressed to achieve the rules of the artifacts and uninstall the stiffness degradation of concrete column.Based on skeleton curve and loading stiffness degradation,the rule of the hysteresis loop of the RC columns with grade 600 MPa steel bars was proposed in detail,with the rule of restoring force characteristics,the restoring force model of the theory skeleton curve geted at the same time.Comparisons of theoretical skeleton curve and experimental results indicate good agreement.