Geometrical imperfections in numerical models of steel bridges

Abstract

Open-section longitudinally stiffened steel I-girders are commonly used in engineering practice as structural elements in bridges. The European standard EN 1993-1-5 tends to underestimate the patch loading resistance of girders with longitudinal stiffeners problematically. Moreover, a structural behavior analysis and a statistical evaluation of girders subjected to bending are missing in literature. This Master’s thesis aims to further investigate the structural behavior of plated structures with special attention to imperfections applied in a GMNIA (Geometrically and Materially Nonlinear Imperfection Analysis) in order to propose appropriate imperfection amplitudes and shapes.

The aim of the research is to analyze the theoretical background of currently proposed, standardized imperfections for plate buckling problems and to recalculate laboratory tests determining the equivalent geometric imperfections. Within this thesis, a numerical sensitivity analysis is carried out for different structure types and failure modes such as flange and web buckling due to bending and web crippling due to a patch load and are compared to lab results.

The research illustrates that for girders subjected to a patch load or bending, the sensitivity of the ultimate load is the largest for small imperfections. In addition to this, the application of smaller imperfections than EN 1993-1-5 still leads to safe side resistances. For girders subjected to bending, the ultimate load decreases compared to patch loading.