Imperfect Columns with Biaxial Partial Restraints

An inelastic theoretical study of the effect of biaxial partial end restraints on the response of hollow rectangular steel nonsway columns with or without biaxial crookedness and residual stresses is presented. The partial end restraints considered have linear, elastic‐plastic, or trilinear moment‐rotation characteristics. The fundamental total equilibrium equations for the problem are derived. An algorithm is presented based on a coupling between an iterative tangent stiffness approach and a finite‐difference scheme for evaluating the spatial response of the materially nonlinear columns. The effect of partial end restraints, as well as the individual and combined influence of crookedness and residual stresses is also explained by means of load‐deflection, and bending stiffness degradation curves. Several interesting conclusions are drawn regarding the behavior of columns as affected by end restraints, imperfections and slenderness.