Directional effects on combined in-plane and out of plane seismic behavior of masonry infills

Unreinforced masonry (URM) infill walls affect both the strength and the stiffness of reinforced concrete (RC) frame structures undergoing lateral loads. Despite being classified as non-structural elements and often neglected in design numerical models, URM infills have a relevant influence on the seismic behaviour of structures. The brittle nature of URM determines a swift degradation of stiffness, strength, and low energy dissipation capacity once the panels are damaged or fail in the one of the in-plane direction failure modes. The aim of this work is to adopt and calibrate a macro-model for masonry infill walls that considers simultaneous in-plane and out-of-plane actions, and apply it to the nonlinear pushover analysis of RC frame structures representative of traditionally and seismically designed buildings. To this scope, a recently proposed URM infill macro-model with in-plane out-of-plane interaction is calibrated with existing experimental data from quasi-static tests performed on two types of clay masonry infill walls that are commonly found both in Italy and other Mediterranean countries. The calibrated elements are included in planar numerical models of RC framed structures representative of the Italian building stock, considering both traditionally and newly designed frames. Nonlinear static pushover analyses are performed on the frames with simultaneous static forces acting on the walls elements in the out-of-plane direction. Results confirm that increasing the out-of-plane loads on the panels induces both cracking and failure of the walls at lower lateral drifts of the buildings. The global force-displacement curves of the frames are also affected.