Ultimate resistance behavior of rectangular concrete-filled tubular beam-columns made of high-strength steel

High-strength steel is permitted in steel structures, whereas, further studies are needed to allow the use of high-strength steel in concrete-filled tubular (CFT) structures. In this study, twelve rectangular CFT columns using Q460-grade steel were tested under eccentric load and the test results were discussed. A nonlinear finite element model (FEM) was developed to predict the load-displacement and ultimate resistance behaviors of the test columns. Parametric studies were conducted using the verified FEM to investigate the influence of aspect ratios, steel strength, and width-to-thickness (h/t) ratio of steel plate. The ultimate resistance calculated by European Code (EC4), American Code (AISC 360) and Chinese Code (CECS 159) is compared with the FEM predictions to evaluate their feasibility in the use of higher aspect ratios, high-strength steel, and various h/t ratios. The results indicate that the three design codes are safe in the design of columns with higher aspect ratios. EC4 is conservative in the design of rectangular CFT columns with high-strength steel up to 690 MPa under its h/t ratio limitation. AISC 360 method can accurately predict the maximum resistance of rectangular CFT columns with steel strength 550 MPa. CECS 159 method is highly conservative and can be safely extended to the use of steel strength up to 690 MPa and plate slenderness ratio 85235/fy.