Nonlinear Analysis Of Ultimate Load-Capacity Of Slender Steel-Concrete Composite Columns

In comparison with steel structures and reinforced concrete structures, steel-concrete composite structures have advantages in many aspects such as high load capacity, good fire and earthquake resisting behavior and much convenience in construction. As a result steel-concrete composite structures have been widely used in civil and industrial building and bridge construction. Steel-concrete composite columns are the important load-bearing members in steel-concrete composite structures, In general cases, columns are subject to biaxially eccentric load and sometimes lateral load with its cross sections in various kinds of shape. In this paper, the ultimate strength of both side pin-ended slender steel-concrete composite columns of arbitrary cross section under biaxial loads or biaxial and lateral loads is studied.In this paper, considering the additional bending moments of the axial load about the lateral displacements (i.e. the second-order effect), an iterative computer analysis procedure is proposed to predict the load-deformation relations and ultimate loads of steel-concrete composite columns of arbitrary cross section. In the procedure, the column is first divided into a finite number of small segments in equal length. The deflection-curvature relation of each segment is determined using the finite-difference method. The final nonlinear algebraic equations are then obtained by means of the equilibrium condition for each segment. The load increment method is used for the solution of the nonlinear algebraic equations. For each load incremental step, a deformed curve for the corresponding state can be determined. Through iteration for all incremental steps the ultimate load can finally be found. During the above iteration, the stress resultants of the concrete in the cross section are evaluated by integrating the concrete stress-strain curve over the compression zone, while those of the structural steel and the steel reinforcement (if any) are obtained using the fiber element method.In order to implement the proposed numerical procedure, a two-module computer program is developed with the computational module in Visual Fortran code and the data-input module in Visual Basic code. Using the numerical procedure, two groups of slender composite columns of rectangular cross section are first analyzed. The obtained results are compared with the corresponding test results and good agreement is found. This demonstrates the validity and accuracy of the proposed method. Meanwhile the effects of slenderness ratio and load eccentricity on the ultimate load-capacity of slender composite columns are numerically analyzed and discussed in detail. Then a T-shaped slender composite column under axial load and two groups of slender composite columns of rectangular cross section subjected to combined biaxial and lateral loads are analyzed, the load-carrying and deformation behaviors of such columns are analyzed and discussed.