Study On The Column Reinforced By Inner Circular Steel Tubes Under Axial Force In Normal Temperature And After Fire

Steel Reinforced concrete (SRC) structures have been widely used in large span structures, super height mansions, heavy weight buildings and etc. Most of these construction are grave engineering or life blood engineering of our country. But still now on, compare to the normal SRC structures, concrete filled steel tubes (CFST) structures and steel structures, the research on the mechanics under axial force of column reinforce by inner circular steel tube is on initial stage, not only in normal temperature but in and after fire also. For this reason, it restrict the widely use and generalization of this structure.In order to change the existing condition, this paper summarize the coherent testing date about this type of structure before, establishing appropriate computational model, using the method of nonlinear finite element analysis, research into the inherent relation of the structure and influencing factor. The main contents of this paper are as follow:(1) Through appropriate computational model, using nonlinear finite element method analyze the effects of parameters on ratio of longitudinal steel bars, different stirrup characteristic values, different yield stress of steel tubes, concrete grades, position coefficient and ratio of inner steel tubes are discussed. And several rational range of these parameters are also given.(2) A simplified formula to estimate the appropriate dimension of inner steel tube is put forward for optimizing the column. Application of this structure type in two actual projects indicates the correction of this formula.(3) After summarizing the thermal properties, mechanical performances of steel and concrete under and after high temperature, the temperature field of the whole cross section are calculated. Also several influencing parameters are discussed.(4) Programming the nonlinear finite element method by APDL language. Through the program, residual load bearing capacity ratio of SRC columns is analyzed. What's more, influencing parameters are discussed in detail.(5) Through the temperature field experiment and bearing capacity under axial force experiment of columns reinforced by inner circular steel tube, the mechanism of fracture is disclosured. After all, the correction of program is also proved.