Diss. Luleå : Luleå University of Technology. 2007

Incremental launching of steel bridges is a demanding undertaking, on the erection site as well as on the designers desk. Not seldom, the structure itself is during the launching subjected to high concentrated forces on the lower flange when passing over a launching shoe or an intermediate support (e.g. column). These concentrated forces, commonly referred to as patch loads, may be of such magnitude that it governs the thickness of the web in the bridge girder. Though, a small increase in web thickness leads to a substantial gain of steel weight of the bridge. Hence also a higher material cost. One solution to this problem is to increase the buckling resistance of the web with the use of a longitudinal stiffener of open (a plate) or closed type (closed profile of e.g. V-shape). The improved patch load resistance is in the european design code EN 1993-1-5 nowadays determined with the help of the yield resistance for the web and contributing parts of the loaded flange reduced with a factor dependent of the slenderness of the web and the influence of one or more longitudinal stiffeners. Parts in the expression for the yield resistance and the reduction factor have been somewhat questioned and over the years a substantial amount of tests and FE simulations of longitudinally stiffened webs has been carried out. This research work has produced a large amount of test data which has been used herein to further improve the prediction of the patch load resistance of longitudinally stiffened steel girder webs. Based on the use of the gathered test data from the literature and previously done research, a calibrated patch load resistance function was developed for both open and closed longitudinal stiffeners. Furthermore, a partial safety factor for the proposal was determined according to the guidelines in EN 1990 (2002). In all, the proposal was shown to clearly improve the accuracy of resistance prediction when compared to other resistance models as well as the EN 1993-1-5.