The influence of beam stiffness on seismic response of chevron concentric bracings

The seismic response of steel chevron concentric bracings is significantly influenced by the flexural behaviour of the brace-intercepted beam. The capacity design criteria provided by current codes aimboth at avoiding the formation of plastic hinge into the beam following the brace buckling and at guaranteeing the energy dissipation by yielding in tension of the brace. However, besides the strength, the beam flexural stiffness has a key role in order to assure the formation of such failure mechanism. Indeed, structures with strong and deformable beams are characterized by poor seismic performance, showing severe damage concentration in the braces under compression, while those in tension behave elastically. In order to investigate this aspect, a comprehensive numerical parametric study is presented and described in this paper. In particular, the influence of beam flexural stiffness on chevron concentric bracings is analysed ranging the ratio between the beam flexural stiffness and the braces vertical rigidity, the beam span, the interstorey height and the brace slenderness. Analytical equations based on the regression of numerical data have been proposed as design aid in order to select the optimal beam stiffness depending on both the required brace ductility and interstorey drift ratio