Stiffened flanges used in steel box girder bridges

Abstract

This paper presents a design method for stiffened flanges used in steel box girder bridges based on a set of design curves that take into account all relevant parameters regarding the ultimate strength of stiffened flanges, including the real boundary conditions for the inplane displacements at the edges. These design curves were developed and calibrated based on the results obtained with nonlinear analysis using the semi-analytical and finite element methods and they were validated by comparison with the results of experimental tests in accordance with the target failure probability of the European standard EN-1990. A comparison between the ultimate strength obtained using the proposal design curves with that obtained using the nonlinear analysis and the current bridge design rules is presented. strained to remain straight). In European standard (EN-1993-1-5 2006) the resistance assessment of webs and internal flanges with longitudinal stiffeners used in steel box girder bridges is performed through the same criterion and independent of the in-plane displacement boundary conditions of the plate. Just apparently both elements may have the same in-plane displacement boundary conditions. Indeed, the webs are usually connected to flanges that possess sufficient rigidity to consider uniform the in-plane displacements at longitudinal edges, while the flanges are connected to webs that usually do not provide this type of constraint and it is more conservative to consider free the in-plane displacements at longitudinal edges, as shown in the work of Ferreira & Virtuoso (2011) through a comparison between numerical and experimental results. The design proposal presented in this paper for stiffened flanges aims to fill a gap in the current European bridge design rules, which should not be applied to stiffened plates with the fully free transverse in-plane displacements at longitudinal edges.