Seismic Damage Mechanism And Design Method Of Steel Reinforced Concrete Columns With Welded Studs Under Combined Torque

Steel reinforced concrete structure combines the advantages of concrete structure and steel structure,and is widely used in high-rise and large-span structures.However,the bonding performance between steel and concrete is poor.By welding studs on the surface of steel,the steel reinforced concrete structure with welded studs can be effectively enhanced.This kind of structure is now widely used in practical engineering.Under the action of earthquake,the structure is often subjected to the combined action of compression,bending,shear and torsion,but the performance of steel reinforced concrete structure with welded studs(SSRC)is rarely reported.The related seismic damage and force transmission mechanism are not clear,and there is no torsion design method for this kind of structure in the corresponding structural specification.Therefore,it is great significance to study the seismic damage mechanism and design method of steel reinforced concrete structure with welded studs under composite torque to guide the practical engineering application of this kind of structure.In this paper,the steel reinforced concrete column with welded studs is taken as the research object.Eight steel reinforced concrete column with welded studs specimens and one steel reinforced concrete column comparison specimen were designed and fabricated.Through the low-cycle repeated test of compression-bending-shear-torsion,the failure process and mode of each specimen were observed.The influence of axial compression ratio,torsion-bending ratio and shear-span ratio on the hysteretic curve,skeleton curve,strength degradation,stiffness degradation,energy dissipation capacity and ductility performance of welded stud steel reinforced concrete column were explored.The seismic damage mechanism and force transfer mechanism of steel reinforced concrete column with welded studs under composite torque were revealed.The corresponding calculation formula of torsional bearing capacity was proposed.The main conclusions are as follows :(1)Under the combined force of compression-bending-shear-torsion,the failure mode of welded stud steel reinforced concrete column is mainly controlled by the torsion-bending ratio.With the increase of torsion-bending ratio,the failure mode of welded stud steel reinforced concrete column changes from bending failure to torsion failure.According to the torsion-bending ratio and shear span ratio,the failure modes of the specimens can be roughly divided into four categories: bending failure,bending-torsion failure,shear-torsion failure and torsion failure.(2)The torque-torsion angle hysteresis curve of steel reinforced concrete column with welded studs is ’S’ shape,and there is obvious pinching phenomenon in the middle of the curve,but the bending moment-column top displacement hysteresis curve is obviously fusiform,and the curve is full.Welded studs can significantly enhance the bearing capacity and ductility of steel reinforced concrete columns under combined torque.(3)With the increase of axial compression ratio from 0.2 to 0.6,the torsional and flexural bearing capacity of the specimens increased by 46.91% and 9.08% respectively.With the increase of torsion-bending ratio,the torsional bearing capacity of the specimen increases,and the maximum increase is 113.46%.However,the flexural bearing capacity of the specimen increases first and then decreases with the increase of torsion-bending ratio,and the maximum increase is 24.79%.As the shear span ratio increases from 2.5 to4,the torsional bearing capacity of the specimen increases by 14.14%.(4)The axial compression ratio is the main factor affecting the strength degradation and stiffness degradation of the specimen,and the torsion-bending ratio and shear-span ratio have little effect.Welding studs can significantly slow down the strength and stiffness degradation of steel reinforced concrete columns;the axial compression ratio and torsion-bending ratio are the main factors affecting the energy dissipation capacity of SSRC columns,and the welding studs and shear span ratio have no significant effect on the torsional energy dissipation of SSRC columns.Considering the rotation ductility and bending ductility,in order to meet the requirements of the specification,the ductility of the specimen SSRC-6(n=0.4,γ=0.5,λ=4)is optimal.(5)Based on the variable angle space truss theory and superposition principle,considering the effect of studs on the interaction between concrete and steel,a practical formula for calculating the torsional bearing capacity of steel reinforced concrete column with welded studs is proposed.The error between the calculation results and the test results is within the allowable range,which is in good agreement and has a certain safety reserve.