High strength steel in chevron concentrically braced frames designed according to Eurocode 8

Abstract

The use of high strength (HS) steel is becoming very popular thanks to their economical and mechanical benefits. Seismic applications represent the rational field to exploit the high performance of HS steel, by means of the “dual-steel” concept that combines the HS with Mild Carbon (MC) steel in order to increase the strength of non-dissipative elements, thus enforcing a ductile overall failure mode. In this paper, a comprehensive parametric study devoted to investigate the seismic performance of EC8-compliant dual-steel chevron Concentrically Braced Frames (CBF) is presented and discussed. Both static and dynamic nonlinear analyses were carried out to investigate the seismic performance for three limit states: damage limitation (DL), severe damage (SL) and near collapse (NC). The investigated parameters cover both geometric and mechanical variables, as the type of columns, span length, number of stories and spectral shape. The analyses showed that the use of HS steel in EC8-compliant CBFs is effective to avoid the damage in the brace-intercepted beams. However, due to the flexibility of the brace-intercepted beams made of HS steel, the bracing members are characterized by severe deformation demand in compression and elastic response in tension. Also, the behavior factors evaluated by means of dynamic analyses are smaller than those recommended by Eurocode 8. The comparison between dual steel CBFs with those entirely made of MC steel showed that in the second case the use of heavier profiles for braced-intercepted beams can be beneficial to reduce the brace ductility demand in compression and to activate their yielding in tension. Thereby, numerical results show that for chevron CBFs it seems more efficient to guarantee adequate stiffness than increasing the material strength for beams. On the contrary, the use of HS steel is effective for columns of the braced spans, reducing the material consumptions while providing satisfactory structural efficiency.