ABSTRACT
The proposed design procedure is based on the application of the kinematic theorem of plastic collapse. It starts from the observation that the collapse mechanism of dual systems under seismic horizontal forces can be considered as belonging to
1 INTRODUCTION
Moment Resisting Frame-Concentrically Braced Frame dual systems constitute a reliable alternative for designers, as they combine the advantages of both structural typologies. The dissipative capacity of beam end sections and the stiffness provided by diagonals allow to obtain high global ductility and limited interstorey drifts, so that both the ultimate and the serviceability limit state requirements can be easily satisfied. Nevertheless, in order to obtain high global ductility, the need to control the location of dissipative zones, i.e. the control of the failure mode, is of primary importance. In particular, partial mechanisms have to be prevented as they undermine the global ductility supply and the energy dissipation capacity of structures. To this scope, modern seismic codes (CEN 2003) require the fulfillment of simple design provisions for traditional structural schemes based on the hierarchy criterion. Even though such requirements are sufficient to prevent soft storey mechanisms, they don’t lead to structures failing in global mode.
