Seismic design criteria for chevron CBFs: Proposals for the next EC8 (part-2)

According to EN 1998-1, chevron concentrically braced frames (C-CBFs) are expected to provide limited ductility due to the interactions between the braces and intercepted beam. As a consequence, EN 1998-1 recommends values of the behaviour factor (namely q = 2 and q = 2.5 in ductility class medium and high, respectively) lower than that (i.e. q = 4) given for other concentric bracing configurations, e.g. both cross and single diagonal CBFs. The research activity presented in this paper is addressed to revise the design rules and requirements of EN 1998-1 for C-CBFs in order to improve the ductility and the dissipative capacity of this structural system. The study is organized in two parts: in the first part design rules recently presented in literature are assessed, while in the second part new design criteria are proposed and validated against the results obtained from incremental dynamic analyses carried out on 2D frames extracted from low, medium and high rise buildings.