Nonlinear finite-element analysis on secondary effect of small eccentric compressive circular column with composite section

Based on the nonlinear finite element principle, layering beam element is used to deduce stiffness matrix of eccentric compressive circular column with combined-section considering material nonlinearity. Iterative method considering second order moment is adopted to calculate the deflection in each section under the first order moment and the second order moment to study the deform regulation considering second order moment under the action of external loads. Example analysis shows that the additional deflection fmax and eccentricity incremental coefficient η for small eccentric compressive circular column with combined-section increases with slenderness ratio and stress level in core concrete increase. In the same length, fmax increases with the increase of ei/d, and η shows contrary regulation.