Experimental Study On Mechanical Properties Of SRC T Column After High Temperature

Steel reinforced concrete special-shaped column structure is a new type of steel skeleton embedded in reinforced concrete structure.It has been widely used in high-rise buildings because of its excellent layout flexibility,the better bearing capacity and seismic performance compared with ordinary concrete columns.As the high-rise buildings are increasingly important role in the modern architecture,the safe of high-rise building structure is concerned wildly and the harm of building fires in the numerous disasters are particularly acute.Due to the high steel radio and the large fire area of steel column,the dangerous degree and the loss of bearing capacity under the high temperature should be reduced than the general concrete column in order to protect personal safety and reduce the economic losses.At the same time,this results also provide a theoretical basis for fire rescue and repair work.It is necessary to research the mechanical properties of special-shaped columns after fire.The mechanical properties of the “T” steel reinforced concrete is researched in this paper.The major work and results are listed as followed.11 “T” SRC columns are designed in this paper which are in constant temperature condition with four side from the self-made electric heating furnace.The mechanical tests of the specimens under different design variables and loading conditions(Horizontal bar spacing,steel ratio,loading angle,eccentricity)were carried out,and the relevant data were collected and analyzed as follows.(1)After high temperature condition,the color of surface concrete changed into grey and white and the local light red with the increase of the temperature.The back of fine cracks at middle section are appeared and powdery material arise on the surface at part of specimens.There are similar trend basically of rising trend at same measuring point.The closer to the surface of “T” column,the faster the temperature increasing.Constant temperature time of 3 hours of each specimen,the sectional temperature changes are basically same.In theory,it can be considered that specimens experienced the same high temperature have similar injury.After 1h,2h and 3h at 600 degree at constant temperature,the free swelling ratio of the specimens is respectively of 0.47%,0.67% and 0.75%,and the axial deformation of the specimens increase linearly with the increase of time.The belly bar displacement of the specimen has no effect on the axial deformation of the specimen,and the axial deformation of the specimen decreases with the increase of the steel radio.(2)The failure process and failure mode of “T” column under axial compression after high temperature are basically same as specimen with normal temperature.Failure form of eccentric compression and axial compression specimens are similar,but specimens with initial crack load and peeling load of eccentric compression are ahead of axially compression members obviously,the final performance of eccentric compression side serious spalling,compression side steel yielding exposed,and the other side appear horizontal crack.Under normal temperature,the specimen was damaged with less than that experienced specimens at high temperature,and the specimens also maintain good integrity;when the specimens with high temperature are destroying,a large number of cracks were produced at the body of column,and the main crack is wide,deformation is more serious as well.(3)The axial stiffness of the specimens at ordinary temperature is significantly higher than that of the specimens under high temperature.The axial deformation of the specimen after high temperature is obviously higher than that in the normal temperature under the same load,and stiffness degradation speed is also faster.Compared with normal specimens,the strength decay rate of specimens under the 60min?120min and 180 min constant temperature were 16.1%,19.3% and 24.8% respectively;loading alone X axis,the loading eccentricity is 40 mm and 80 mm respectively.The strength of the specimens is reduced by 9% and 14.1%,respectively;the ultimate deformation of the specimens under eccentric compression increases with the increase of eccentricity,which shows a linear trend.Belly bar spacing for high temperature pressure specimens pre axle stiffness had less impact;in the middle term of loading,axial compression stiffness of T-04 which is 200 mm abdominal bar spacing is more better than that which is 300 mm,400mm,and the ultimate bearing capacity has no obvious change with the change of horizontal belly bar spacing;the steel content increased 15% after high temperature,and the residual bearing capacity increased by 24%;the difference of loading angles have less influence for the beginning vertical deformation-load curve to specimens after high temperature condition.However,when the specimens are close to the limited load,the vertical deformation of the specimen with 45 degrees loading angle is obvious than that of the loading angle during 0 degrees and 90 degrees.