ACCIDENTAL TORSION WITH INDUSTRIAL BUILDINGS – OVER‐CONSERVATIVE RULES IN EC8

Abstract

ABSTRACTThis paper is related to seismic design of industrial steel buildings, such as warehouses and plant skeleton structures. Designers will be encouraged to skip rules of EC8 under certain circumstances, which lead to over‐conservative results.Seismic design according to EC8 contains a general clause on accidental torsion. There, the possibility of an offset of the resulting masses within a storey and the spatial variation of the seismic motion is considered. Consequently, this leads to an unintended torsion (e.g. rotation of the structure about its vertical axis). Different magnitudes of additional loads in the vertical bracing planes may follow depending on the location of the bracing in the structure. Even in the favorable case of the bracing being located in the outmost walls (which is given in typical warehouses anyway), the bracing forces are to be increased by a factor of 1.3 according to the provisions of EC8 lateral force method. In this paper, the determination of the bracing forces is followed in two examples of industrial buildings, a warehouse with a crane bridge and a plant skeleton structure with heavy equipment on different levels. Based on these examples it will be shown, that the provisions of EC8 are way too conservative. Advice is given, on how the designer can come up with robust, but much lower forces for the vertical bracing planes.