Analysis On The Working Behavior Of Square Cfst Frame Columns With Defects

Because of the Concrete-Filled Steel Tubular (CFST)'s superior working capability, it has been widely used in building engineering. Up to now, the research of Concrete-Filled Steel Tubular is mainly based on core concrete with the good quality.Only some of experts studied the working capability of Concrete-Filled Steel Tubular with the disengaging between steel and concrete.Based on one actual engineering, this paper is to analyse the working capability of Concrete-Filled Steel Tubular with quality defects (cavities or holes) which could emerge under the inner-ring plate during the core concrete pouring. The defects are liable to occur in the concrete-filled steel tubular with small side-lengths or small diameter in the pouring process.In this paper,considering the material and geometrical nonlinear questions simultane-ously,I used the three-dimensional solid element solid45,solid65 and beam4 to establish a framework as the finite element model by the structure finite element analysis software ANSYS10.0. In the positions where the core concrete defects are most liable to occur. I choosed one position where if the defect emerge, the ultimate bearing capacity of the framework may be influenced.In this model,I designed 4 concrete defects (cavities or holes) from small to large size, which are under the inner-ring plate of square Concrete-Filled Steel Tubular column in the first floor of framework. And then firstly, I compared the stress of square Concrete-Filled Steel Tubular with defects under the gravity and the severe Earthquake(the equivalent horizontal load calculated by the bottom shear method) with the stress of Concrete-Filled Steel Tubular without defects.Secondly, I compared the behavior of Concrete-Filled Steel Tubular column with the inner-ring plate and column without the inner-plate.To select the constitutive relationship of the core concrete,I used the miso model (linear isotropic hardening model) and the Drucker-Prager model(the ideal elasto-plastic material response).And also considered two cases of the concrete Poisson's ratio:remaining unchanged during the loading process and changed at the later stage of the loading.According all of the above,I designed 20 models in total in order to simulate the actual situation correctly.After analysis, I roughly quantified how much influence the vertical length changing of the concrete defects (cavities or holes) with a particular width would exert upon the working behavior of Concrete-Filled Steel Tubular columns.And I also quantified the difference of the working behavior between Concrete-Filled Steel Tubular columns with and without the inner-ring plate at the aspect of the maximum stress influence to the steel tubular. Finally I simply discussed the influence which the core concrete defects impact to the framework's ultimate bearing capacity.