Tragverhalten an Gurtdickensprüngen geschweißter Biegeträger

Load carrying behaviour at flange thickness transitions in welded girders.

Flange thickness transitions and cover plates constitute two of the most common constructional details used to adapt the flexural resistance of bridge girders to variable bending moment distributions. The sudden change of stiffness distribution within the cross-section at these details causes additional local forces and stresses that cannot be properly taken into account by classical beam-theory calculations. The study presented in this paper shows that on the one hand, the longitudinal welds between web and flange plates are subjected to additional longitudinal shear forces, as well as transversal forces in the web plate's plane. On the other hand, the usually eccentric disposition of the flange plates causes considerable local bending stresses in these plates. The latter also affects the buckling strength of the flange plates when these are loaded in compression. Although these effects have been known in principle for some time, their correct inclusion in practical calculations has gained significance over the last years due to the prevailing trend towards the use of thicker plates of higher steel grades designed with higher stress utilizations. The inclusion of these effects in current design procedures is, at present, treated with rather pragmatic approaches; therefore, the objective of this paper is to illustrate the realistic stresses in flange thickness transitions by means of case studies, and to discuss the effects that these stresses have on the serviceability, fatigue and buckling strength of the girders.