Unified Solution Of Axial Compression Ultimate Bearing Capacity For Concrete-filled Regular Polygonal Steel Tubular Column With Initial Stress

Concrete-filled steel tubular column is one of the common composite structure, with several advantages such as simple structure, convenient construction, easy maintenance, good economic applicability, for which it has been widely used both at home and abroad.During the construction of the concrete filled steel tubular column, the initial stress caused by the dead weight of the steel pipe, construction equipment, and the dead weight of the unset concrete is generated. Relevant studies have shown that the initial stress of the steel tube has certain effect on the bearing capacity of the concrete-filled steel tube.Based on the twin shear unified strength theory, with the influence of the initial stress of steel tube, intermediate principal stress and tensile compression ratio of materials taken into account, this thesis is intended for an analysis of the forced mechanism of concrete-filled square steel tubular short columns, dividing core concrete into effective constraint region and invalid constraint region, introducing the slenderness ratio reduction coefficient, and establishing the unified solution of axial compression ultimate bearing capacity in concrete-filled square steel tubular short columns, with the initial stress considered. By utilizing the twin shear unified strength theory, the axial compression ultimate bearing capacit of the concrete filled steel tubular columns with regular octagon is deduced. With the variable in the number of edges introduced, the general formula for the axial ultimat bearing capacity of concrete-filled steel tubular columns in equilateral polygon section is obtained. The correctness of the formula is verified by comparing with the experimental results and numerical simulation results in the references. According to the simulated data employed in the references and the sample data drafted in practical engineering, the thesis uses ANSYS to build the model of square section, regular octagon section, regular hexagon concrete-filled steel tubular columns, in order to give a nonlinear finite element analysis. The analysis results are compared with the calculation results of the formula for a mutual verification of the accuracy in both results, based upon which a debate is conducted on the effects of various parameters. Research results show that: the use of twin shear stress yield criterion in calculation can more clearly reflect the effect that initial stress of steel tube exerts on the axial ultimate bearing capacity of concrete-filled steel tubular columns; the initial stress of steel tube reduces the axial ultimate bearing capacity of concrete-filled steel tubular columns. the axial ultimate bearing capacity of concrete-filled steel tubular columns with the initial stress considered increases with the increase of side pressure coefficient, parameters of the unified strength theory and stability factor considering slenderness ratio, and, decreases with the increase of initial stress and broad width-to-thickness ratio in a broad sense.The research results have certain engineering significance for the study of concrete-filled regular polygonal steel tubular column considering the initial stress and provide a theoretical basis for the design and construction of the concrete-filled steel tube structure.