An implementation for 2nd-order M-N coupling and geometric stiffness adaptation in tapered beam-column elements

The present work outlines a computational approach, based on the so-called Finite Analytic Method (FAM), to deal with second-order effects in the structural analysis of tapered members accounting for geometrical nonlinearity by using only one element per physical member. The proposed modelization considers the equilibrium in the deformed configuration of a “beam-column” element, by addressing the resulting mechanical coupling between bending moment and axial force (M-N interaction). A flexibility-based method is developed, to derive the force-displacement relations of the finite element, by obtaining its flexibility and stiffness matrices. Through Gauss-Lobatto integration, the stiffness coefficients capturing second-order geometrical effects are consistently evaluated, to achieve the complete stiffness matrix. Examples and comparisons with reference studies are provided, in order to prove the effectiveness of the proposed methodology. Results on the critical load evaluation of sample tapered members are delivered.