Out-of-plane seismic behavior of non-framed unreinforced masonry walls with pre-existing seismic damage

Abstract

This paper presents a numerical investigation into the influence of seismic in-plane (IP) pre-damage on the seismic out-of-plane (OOP) response of non-framed unreinforced masonry (URM) walls. These effects, referred to as IP/OOP interaction effects, are rarely investigated for non-framed URM and remain insufficiently understood. Consequently, seismic design and assessment provisions for non-framed URM neglect their potential impact on the vulnerable OOP response of URM. The paper conducts a parametric analysis using the high-fidelity modeling approach developed by the authors and previously validated against the IP and OOP responses of non-framed URM walls. The approach represents URM unit-by-unit via 3D finite-element nonlinear expanded blocks and cohesive-frictional zero-thickness joints. Four wall geometries are considered and pre-damaged by static cyclic IP loading under varying pre-compression levels and boundary conditions. Different IP pre-damage states are used as initial conditions for static and dynamic OOP analyses. Dynamic simulations employ signals representing induced and tectonic earthquakes. OOP stiffness reduction is also tracked through modal analyses. The results show that one-way spanning walls exhibit almost no sensitivity to pre-damage, whereas two-way spanning specimens experience up to 30% and 33% reductions in OOP stiffness and strength at severe pre-damage state. Moreover, under specific conditions, such as opening walls under low pre-compression, does pre-damage alter the OOP failure mechanism and cause more drastic stiffness reductions. Among all configurations, only the pre-damaged one-way spanning walls collapse under induced seismicity, and only at intensities higher than real events. Finally, good agreement is observed between static and dynamic simulations results under pre-damage.