ABSTRACT
The superstructure of a steel- or composite bridge functions as a continuous beam supported by multiple launching bearings on the piers during the launching process. As the superstructure approaches the subsequent pier, a segment of it temporarily exhibits the behaviour of an extended cantilever. Consequently, significant bending moments and reaction forces arise at the final bearing. The interaction of internal forces induces a biaxial stress state within the cross-section. This load case is typically decisive for the web's buckling verification and structural design. Until recently, during the design of the Heidingsfeld viaduct (2015), the adverse effect of biaxial compression was not considered in buckling analysis when applying the reduced stress method according to EN 1993-1-5 (EN 1993-1-5 2019). To assess this effect, extensive large-scale experimental investigations were conducted during the design phase of the Thulba viaduct at the Chair of Metal Structures at the Technical University of Munich. This publication presents the findings of these investigations, with a comparative analysis of the consideration of biaxial compression effects in the revised version of EN 1993-1-5 (EN 1993-1-5 2019). Furthermore, discrepancies between the center lines of the superstructure webs and the launching bearings are frequently observed. These eccentricities may result from misalignments of the launching bearings, the required air gap to the lateral guide, or variations in panel thickness along the superstructure. Notably, such eccentricities are not accounted for in the buckling verification as per EN 1993-1-5 (EN 1993-1-5 2019). There is ongoing discourse regarding the extent to which these eccentricities influence buckling behaviour and whether their consideration in the buckling verification is necessary. In cases where launching bearings, such as rocker systems incorporating an elastomeric bearing between the superstructure and the launching beam, are employed, the reaction forces resulting from the nonlinear material behaviour are also a subject of analysis. Reference (Thomas et al. 2022) presents the effects of buckling resistance as a function of load eccentricity for various parameters and launching bearing types. A comparison of buckling resistance, involving analyses from (Mensinger et al. 2017) and (Kuhlmann et al. 2021) as well as buckling verification in accordance with (EN 1993-1-5 2019), is provided in (Thomas et al. 2021). A comprehensive synthesis and a novel approach for incorporating eccentric load applications and clamping effects within the buckling zone are presented in (Thomas 2023). This paper presents initial investigations into the influence of elastomeric bearings and the challenges related to capturing the nonlinear material behaviour response within the numerical model. The results demonstrate that load eccentricities, when combined with elastomeric bearings, do not adversely affect the buckling behaviour.
