Code-Oriented Floor Acceleration Response Spectra of RC Framed Buildings Accounting for Nonlinear Response of Masonry Infills

. Modern code-oriented elastic floor response spectra formulations for RC framed structures do not take into account effects of non-negligible nonstructural components in terms of mass and stiffness, such as masonry infills (MIs). MIs nonlinear behaviour can be represented through the combination and mutual interaction between the in-plane (IP) and out-of-plane (OOP) responses. The present work is aimed at identifying the effect of IP and OOP nonlinear modelling assumptions on floor acceleration response spectra, consistently with the required seismic intensity level for simplified verification of life-threatening nonstructural elements. To this end, a spatial one-bay multi-storey shear-type model is considered as equivalent to infilled RC framed buildings with common double-leaf MIs. Additional variability of the following design parameters is considered: number of storeys (three, five and seven); behaviour factor (low, 1.5, medium, 3, and high, 4.5); OOP strength of MIs, with lower and upper bound values corresponding to one- and two-way arching mechanisms, respectively. A recently proposed computer code, that includes a five-element nonlinear infill macro-model comprising four diagonal OOP beams and one (horizontal) central IP truss, is considered for the numerical investigation. The proposed algorithm modifies stiffness and strength values of MIs in the OOP direction on the basis of simultaneous or prior IP damage and vice versa. Moreover, a lumped plasticity model describes the inelastic behaviour of RC frame members.