Study On The Mechanical Performance Of Concrete-Filled Rectangular Steel Tubes

Steel house is one of main structures that will be developed in"the 11th five years plan"of China. Because of the typical mechanical performance of concrete-filled rectangular steel tube (CFST), it will be more extensively adopted in steel dwelling houses. However, nowadays the study on CFST hasn't been deeply carried out. Correlative calculation theories and the inner working mechanics of CFST haven't been well developed. Therefore it's necessary to carry out farther study on the finite element modal and calculation of CFST.Through the analysis of research findings on constitutive relationships of steel tube and in-core concrete in China and abroad, the constitutive relationship of steel tube was acquired and the relationship of in-core concrete was also acquired considering the confining effect of steel tube to in-core concrete and the effect of depth-width ratio.At present in China there have three calculation theories about CFST. They are Uniform Theory, Semi-steel Theory and Superposition Theory separately, the main difference of which is the idea about the interface of steel tube and in-core concrete. Here a group of push-out tests on CFST and their finite element analysis were carried out. Based on experimental results and correlative research findings in China and abroad, the typical load-displacement curve of the interface was acquired. It can be concluded that in CFST the connection between steel tube and in-core concrete is"weak".On the basis of constitutive relationships of steel tube and in-core concrete, a series of finite element program was worked out adopting FORTRAN language in order to study the mechanical performance of CFST under axial compression load, bending load and compression-bending load. And their results were compared with correlative experimental results in China and abroad to testify the validity of these programs. Based on these programs and experimental results of super-sonic flaw detected tests and parting tests on CFST, a series of calculation equations was put forward. And by compared with experimental results, it can be easily found that these equations could effectively estimate the mechanical performance of CFST. So they can be referred by engineering practices. Then a VB program was developed, and it could be easily adopted in engineering practices.The state of art of the research on the dynamic behavior of CFST was analyzed. Then the constitutive relationships of steel tube, in-core concrete and their interface under cyclic loading were acquired. And finite element program to study the hysterestic performance of CFST was worked out. In order to testify its validity, it was compared with correlative experimental results. On the basis of this program, a simplified restoring force modal of CFST was developed, and by compared with experimental results it could be conclude that it's effective.