Collapse mechanisms and load–deflection curves of unstiffened and stiffened plated structures from bridge design

• Collapse mechanisms for (un)stiffened plates with trapezoidal stiffeners by FEM.
• Simplified determination of load–deflection curves of such plates.
• Proposal for verification as alternative to the given methods in design codes.

Cross sections of modern bridges are generally build with stiffened plated elements. The verification methods given in Eurocode EN 1993-1-5, to obtain the ultimate buckling resistance of plated structures, result in a time consuming procedure. In addition, the methods are mainly based on the elasticity theory and reduction factors from e.g. experiments are needed. Therefore, an alternative approach to obtain the ultimate resistance of unstiffened and stiffened plates is used. The method is based on a strain-dependent and geometric nonlinear yield-line theory including imperfections. This theory makes it possible to approximate the decreasing part of the load–deflection curve of such stability sensitive structures. The ultimate resistance, as maximum of the load–deflection curve, is approximated by a defined limit value. Therefore, the use of additional reduction factors is not necessary. Collapse mechanisms, which have been determined with the Finite Element Method (FEM) beforehand, are needed in order to apply the yield-line theory.