Design And Analysis Of Arbitrarily Shaped Steel-Concrete Composite Columns

Concrete-encased composite columns are the important load-bearing elements in many steel-concrete composite structures. The behavior and strength of composite columns of rectangular cross-section with doubly symmetric structural steel have been widely examined by domestic and overseas researchers through experimental and theoretical ways. Many simplified design equations and computer-based analysis methods have been proposed. However,the analysis and design procedures for composite columns of complex cross sections are still not available. The aims of this paper are to develop a general computer-based analysis method,which is suitable for any composite columns with either regular or irregular cross sections and meanwhile to evaluate some existing simplified design equations using this proposed method.In this paper an iterative computer-based analysis method is first proposed and the corresponding visualized computer program is developed. The proposed method was based on several reasonable assumptions including that plane sections before deformation remain plane after deformation. In this method the stress resultants of concrete in the cross section are evaluated by accurate integrating method and the resultants of structural steel and reinforcing bars are obtained using the fiber element method. The final nonlinear algebraic equations are solved using an iterative Quasi-Newton procedure based on the Regula-Falsi numerical scheme. The proposed method and the corresponding computer program are then used to achieve the cross-sectional design and to determine the load carrying capacities of several composite columns with different sectional shapes. The obtained load capacities are also compared with the available experimental results and good agreement is found. Based on the above contribution the method is used to evaluate the accuracy and limitation of the simplified design methods proposed by the Chinese JGJ 138-2001 Specification and YB9082-97 Specification,which are only suitable for concrete encased composite columns of rectangular cross section with doubly symmetric structural steel. Several valuable conclusions and suggestions for practice design are obtained. Finally according to the load-capacity superposition concept,a simplified design equation for determination of the load capacity of circular composite columns with H-shaped and box-shaped structural steel is proposed. Through comparison with the accurate computer-based method,it is found that the proposed simplified equation is accurate enough and can meet the requirement ofpractical applications.