Experimental Study On Mechanical Properties Of Steel Reinforced Concrete Cross Shaped Columns After High Temperature

The steel reinforced concrete special-shaped column structure is a steel-concrete composite structure composed of steel bar,reinforced bar and concrete.The steel reinforced concrete special-shaped column structure has the advantages of flexible arrangement,high utilization rate of room,large bearing capacity,large rigidity and good seismic performance compared with traditional reinforced concrete structure.Compared with steel structure,it has many advantages,such as good fire resistance,good local and overall stability,low cost and low cost.Therefore,with the development of modern architectural diversity,the steel concrete special-shaped column structure still occupies a place of many architectural forms,and more and more layers and high rises have been applied to this structure,even in recent years,the assembly type steel concrete column structure has appeared.The steel reinforced concrete special-shaped column structure is very important for the development,optimization and improvement of the seismic performance of many high-rise buildings in China.In addition,the steel ratio of the steel reinforced concrete structure is much higher than that of the ordinary reinforced concrete structure.Once the fire happens,the impact on the building structure is very large.In this paper,the temperature field analysis of 1 normal temperature contrast specimens and 7 post high temperature steel concrete cross column specimens,the fracture morphology after high temperature,the failure mechanism in the static loading test,and the data analysis are carried out,and the following conclusions are drawn as follows:(1)Through the high temperature test of 7 steel reinforced concrete specimens,the temperature field and axial displacement of each section are measured.The test results show that the surface color of cylinder concrete is basically dark red and partly white.And the whole column is full of crack,and it is found that many members have cracks in the back and limb of the limb 30 mm,and the cracks are long or short,but all are vertical cracks.The temperaturechange of each test point in high temperature is basically consistent with the temperature rise curve,and the temperature in the interior point of the concrete is getting lower and lower,and the heating curve of the different components is different,but the trend is basically the same.The maximum axial deformation of 60 min,120min and 180 min at constant temperature is3.85 mm,4.32 mm and 4.66 mm respectively.It can be seen that the maximum axial deformation increment is approximately linear with time.(2)By observing the failure process of static loading test,the failure process can be roughly divided into the non cracking stage,the crack stage and the failure stage.In the whole static loading test,all the specimens show a common character — the crack starts from the upper and lower end of the enlarged head,and then the continuous loading will occur in the column.The failure mode of the axial compression steel reinforced concrete specimen is the shear cracks on the most lateral concrete.The final section steel is yielding under compression and the whole is subjected to axial compression failure.(3)The ultimate bearing capacity of steel reinforced concrete cross column XGS-02~XGS-04 specimens after fire is only 73%~79% of normal temperature.The initial stiffness of the axial compression specimen decreases with the increase of the constant temperature,and the axial compression stiffness attenuates first and then decreases,that is,the0-0.6Pu axial compression stiffness increases and the 0.6Pu-Pu axial compression stiffness decreases.(4)XGS-04~XGS-06 comparison and analysis of steel reinforced concrete specimens with different eccentricity.The ultimate bearing capacity of 0mm,40 mm,80mm specimens,XGS-04,XGS-05 and XGS-06 is reduced by 27%,35.5% and 50% respectively.The bending stiffness of each specimen decreases with the increase of axial load,and the bending stiffness decreases with the increase of the eccentricity.After the high temperature,the axial displacement load curve of the eccentric loading test specimen XGS-05 and XGS-06 is more gentle than that of the axially loaded specimen XGS-04,and it has a stronger deformation ability in the later period.(5)The increase of eccentricity has a significant effect on the cross section columns of high temperature steel reinforced concrete.The ultimate bearing capacity of specimens XGS-06,XGS-07 and XGS-08 decreased by 50%,45.5% and 43% respectively when loadingangles were 0 degrees,22.5 degrees and 45 degrees.With the increase of loading angle,the flexural rigidity of specimens also increases.