Experimental Study On Seismic Behavior Of T-shaped Steel Reinforced Concrete Special Shaped Columns After Fire

Steel reinforced concrete special-shaped columns with profile steel configured by section can significantly improve the bearing capacity,stiffness,displacement ductility and deformation capacity of the structural system,and its application is much widely.Fire damage,resulting in the degradation of the performance of concrete and internal steel materials,will inevitably lead to changes in the seismic performance of steel reinforced concrete special-shaped columns.However,there is no report about this aspect at home and abroad.So in this paper,experimental study on fire damage under different test parameters and the seismic resistance of the earthquake of T shaped steel reinforced concrete special-shaped columns are studied.The main work contents and conclusions are as follows:1.The fire damage of 7 T-shaped steel reinforced concrete special-shaped columns is experimental studied.The apparent phenomena and law of crack development after the fire are analyzed in depth,as well as the temperature field distribution and law of vertical deformation of cross section under fire.The experimental results show that:(1)After the fire damage,the color of concrete surface is obviously changed and there are plenty of surface cracks;(2)The temperature rise rate and section temperature of concrete decrease with the increase of distance from the surface of the fire.There is an obvious temperature platform near 100℃;(3)The thermal inertia of concrete is obvious under fire,the change of concrete temperature lags behind furnace temperature and the internal temperature lags behind the external measuring point;(4)Under fire,the deformation of the special-shaped column is mainly caused by temperature,the thermal expansion of the specimen is subjected to axial deformation and presents growth.2.Experimental study on seismic behavior of 7 columns under fire damage and 1 column untouched by the fire is carried out.The stress characteristics,failure process and the final failure mode of the test columns are analyzed.The experimental results show that:(1)The failure process of special-shaped columns undergoes elastic stage,yield stage and failure stage.Each stage has different stress characteristics and experimental phenomena;(2)The stirrup effective plays so effective an role in binding of concrete that can effectively transfer the shear force and prevent the shear lag;(3)The axial compression ratio is increased,and the stress of the member section is increased.Under the action of bending moment,the upper and lower part of the back surface of the wing edge is more likely to occur bending and crushing damage;(4)The increase of shear span ratio reduces the degree of crushing damage of concrete at the upper and lower sides of the back side of the wing;(5)Fire damage,weakens the role of the flange.The most unfavorable longitudinal shear section is closer to the edge of wingcompared with columns not affected by fire.3.The seismic behavior of T-shaped steel reinforced concrete special-shaped columns after fire is analyzed in depth.The analysis shows:(1)Before the cracking of concrete,the distribution of strain along the height of the section is still in line with the assumption of plane section.The flat section assumption is no longer valid after cracking of concrete.;(2)The hysteretic behavior,displacement ductility and energy dissipation capacity of specially shaped columns is obviously weakened by fire damage.The yield strength and ultimate bearing capacity of the component is reduced.The attenuation of strength and stiffness is accelerated;(3)Axial compression ratio is an important factor affecting the seismic performance of structures and members.The increase of axial compression ratio makes the compression zone’s height of the cross section increase,rotation of cross section restricted,the initial stiffness and strength of the component improved.The hysteretic energy dissipation increases with the increase of the displacement.But the possibility of brittle failure and deformation instability is increased.Then the displacement ductility of the component is reduced.In the late stage,the intensity attenuation and stiffness degradation are accelerated;(4)Shear span ratio is an important factor that affects the seismic behavior of T-shaped steel reinforced concrete special-shaped columns after fire.The increase of shear span ratio reduces the initial stiffness,ultimate bearing capacity and energy dissipation capacity of the component.But its intensity decay is slow.While the shear span ratio is 2 or so,the ductility changes worse with the increase of the shear span ratio.The displacement ductility increases with the increase of shear span ratio at about 2 or so;(5)The displacement ductility and hysteretic energy dissipation capacity of the component can be improved remarkably by the increase of the ratio of the coupling.And the bearing capacity of components improved,component stiffness and strength degradation delayed.