NUMERICAL MODELLING AND ANALYSIS OF ECCENTRIC BRACING WITH VERTICAL SHEAR LINKS

Eccentric steel bracing with a vertical shear link is a type of seismic force resisting system that could be selected for seismic retrofitting or upgrading of existing structures. Previous studies have shown that short links with relatively small sections could develop peak shear forces larger than usually predicted values, because of a combination of geometrical charac teristics of the link cross section, the link length and the boundary conditions. The peak shear force could be limited by the ductility demand as well as by the occurrence of local and/or global buckling phenomena. This paper explores the response of eccentric bracing compris ing the link as well as the diagonal members, looking for the overall behavior. To this end, realistic eccentric bracing systems have been first designed. The case studies were generated starting from the analysis of an existing RC school building in Italy. The existing building was selected within an Italian research project sponsored by the ReLUIS consortium and the De partment of Civil Protection in Italy. The response of the existing RC structure was upgraded by designing a steel eccentric bracing system to fulfil the design criteria of the Italian seismic code. Then, the steel bracing system was modelled by means of the finite element (FE) meth od. This paper describes shortly the design criteria and the consequent results. Then, the FE models and the analyses are described in detail, especially discussing the global behavior in terms of steel strain hardening and overall system stability at the peak inelastic deformation demand estimated at the design stage.