Second-order plastic-zone analysis of steel frames – Part II : effects of initial geometric imperfection and residual stress.

Abstract

The application of a second-order plastic-zone formulation to study the minimum requirements needed to arrive at the so called advanced analysis concept, where an individual member’s check is simplified or even unnecessary, is presented in this paper. A companion paper provides the theoretical background for this formulation. These requirements appear in specifications and refer to the unavoidable imperfections of steel structure construction leading to premature collapse. The structure’s out-of-plumbness and members’ out-of-straightness form the initial geometric imperfections, affecting building stability and lateral drift, but are justifiable under manufacturing and erection tolerances. Unequal cooling of a steel section, after the rolling or welding process, creates residual stress that increases the plasticity path. As the plastic zone analysis accounts for these three imperfections in an explicit way, alone or combined, this study shows a brief review, computational implementation details and numerical examples. Finally, this work makes some recommendations to find the worst initial imperfect geometry for some loading cases.