Unreinforced masonry (URM) is known to have negligible tensile capacity and hence shows brittle behaviour under lateral action (e.g., earthquakes). Even a moderate level ground motion could trigger damage and inelastic response. In addition, the inherent stiffness eccentricity in plan configurations and randomness in seismic incidence angle could lead to in-plane (IP) and out-of-plane (OOP) bidirectional interactions in URM walls. Potential weak links, such as poor floor-to-wall and wall-to-wall connections, can aggravate the interaction. Neglecting such interaction in the nonlinear finite element (FE) modelling of the URM buildings would significantly underestimate the overall force capacity. With regard to micro- and meso-models, accuracy in capturing interaction effect is adequately demonstrated by previous research; however, no existing macro-element models available in the literature consider this. Micro and meso-models are less preferred than macro-models because of difficulty involved in obtaining reliable material properties for masonry and high computational demand. Hence, the primary objective of this research work is to develop a reliable 3D numerical FE macro-element for URM piers considering IP-OOP interaction for accurate and quick assessment.
The current seminar will focus on developing nonlinear FE micro-models for a parametric study on IP-OOP interactions in URM piers after summarising details of the 3D macro-element already formulated under equivalent frame approach and presented previously. For the parametric study, FE micro-models with different aspect ratios and precompression levels (25 cases and 250 simulations) are developed in OpenSees by explicitly modelling bricks and mortar. A refined layered shell element validated for both IP and OOP mechanisms is used to capture interaction effect (OOP transverse shear failure along with IP failure mechanisms). Analytical expressions for the interaction curves are developed based on the outcome of the parametric study, which showed interaction is significant in shear-dominated piers. Finally, a new pushover analysis framework is proposed to address the need to simulate the bidirectional interaction effect in URM buildings with rigid diaphragms because of varying seismic incidence angles.