Experimental Study On Mechanical Properties Of Recycle Aggregate Concrete-Filled Steel Tubes After Fire(High Temperature)

The recycle concrete-filled steel tube, which forms with the pour of the recycled concrete to the steel tube and makes steel tube and core concrete common withstand external loads, brings the superiorities of recycle concrete and steel tube into play,and provides an important way for the application and development of recycled concrete in the future. Domestic and foreign scholars have done a lot of research about the mechanical property study of normal concrete-filled steel tube and recycle concrete-filled steel tube under room temperature and normal concrete-filled steel tube under high temperature. The mechanical property study of the recycle concrete-filled steel tube under constant high temperature has been reported rarely. Therefore, this thesis conducted an experimental study about its mechanical properties. The research content is as follows:(1) In order to study the ultimate bearing capacity and deformation capacity of the recycle concrete-filled steel tube after fire(high temperature), with recycled coarse aggregate replacement ratio, constant temperature, constant temperature time, the core concrete strength as the main parameters,the experiment of axial compression on28circular recycle concrete-filled steel tube columns under constant high temperature is done, with the comparative experiment on16circular normal concrete-filled steel tube columns. Through this test, the whole mechanical process and failure pattern of all specimens were observed, the strain-stress curves of recycled aggregate concrete-filled steel tube were obtained, and the influence of recycled coarse aggregate replacement ratio,constant temperature,holding time, the strength of core concrete to the axial bearing capacity, elastic modulus, deformation, stiffness degradation, energy dissipation capacity of the specimen were analyzed. Used Han Linhai’s the capacity calculation formula about normal concrete-filled steel tube under high temperature to calculate the axial compression bearing capacity of the test specimens, compared with the test results, finally according to the actual results of the experiment, we put forward the strength calculation formula of axial compression short column after fire(high temperature),which is influenced by the recycled coarse aggregate replacement ratio,the constant temperature, the core concrete strength.(2) In order to study the mechanical properties of circular recycle concrete-filled steel tube columns under eccentric compression and constant high temperature,9specimens with different replacement radio of recycled coarse aggregate,constant temperature were tested under the monotonic static loading.The failure modes were observed,and the curve of the entire loading process as well as the strain distribution over the cross section were obtained, the influence of recycled coarse aggregate replacement rate and constant temperature to the ultimate bearing capacity and energy dissipation capacity of the specimen were analyzed.