Failure Mode and Drift Control of MRF-CBF Dual Systems

Abstract

In this paper, a new method for designing moment resisting frame (MRF) - concentrically braced frame (CBF) dual systems failing in global mode is presented. Starting from the analyses of the typical collapse mechanisms of such structural typology subjected to seismic horizontal forces, the method is based on the application of the kinematic theorem of plastic collapse. Beam and diagonal sections are assumed to be known quantities, because they are designed to resist vertical loads and horizontal forces, respectively. Therefore, the column sections are the only unknowns of the design problem. Column sections are obtained by imposing that the equilibrium curve corresponding to the global mechanism has to lie below all the equilibrium curves corresponding to the undesired collapse mechanisms within a displacement range compatible with the local ductility supply of dissipative elements. Such procedure has been applied to design several MRF-CBF dual systems and has been validated by means of non-linear static analyses aimed to check the actual pattern of yielding.