Experimental Research on the Axial Compressive Capacity of Thin-Walled Concrete-Filled Square Steel Tubular Columns

Tests of 10 concrete-filled thin-walled square steel tubular columns under axial compression were conducted, the influence of slenderness ratio, wall thickness and concrete strength on the failure pattern, load-displacement curve, ultimate bearing capacity and Poisson's ratio of the specimens were studied. The results showed that the loading process of concrete-filled thin-walled steel tubular column was similar to that of ordinary concrete-filled steel tubular cloumn. Generally, it could be divided into three stages:elastic stage, elastic-plastic stage and descending stage. The failure of the specimens in the test was that the core concrete was crushed and there was a circumferential buckling band outside the steel pipe. The finite element software was used to establish the model of concrete-filled thin-walled steel tubular column and verify its effectiveness and reliability. The analysis results showed that when the steel ratio of member section was certain, the influence of concrete strength on the combination effect of steel-concrete structure was very obvious. For thin-walled members with steel ratio of 0.02 to 0.06, the combination efficiency of steel-concrete structure could be improved by using concrete with strength grade of C20 to C50.For the stability bearing capacity, it was found that the stability coefficient under different variation parameters could be expressed by a single equation with the regular slenderness ratio as the independent variable. Finally, referring to Technical Code for Concrete Filled Steel Tubular Structures(GB 50936-2014), a simplified calculation formula for the axial compressive bearing capacity of concrete-filled thin-walled square steel tubular columns was proposed, and the calculated values were in good agreement with the measured values.