Development of Advanced Equivalent-Frame Models for the Nonlinear Seismic Analysis of Masonry Structures

The pronounced seismic vulnerability of unreinforced masonry (URM) structures and their extensive presence worldwide has prompted significant interest in developing strategies for an appropriate assessment and retrofit of the existing stock on the one hand, and for the design and detailing of new construction on the other hand. The seismic performance of existing URM buildings is generally governed by the activation of local overturning mechanisms, as they have been typically built without adequate consideration of horizontal actions. However, even though modern building codes and guidelines have stressed the importance of inhibiting local out-of-plane failure through structural interventions or new construction details, the in-plane seismic capacity of masonry walls might still be inadequate to withstand the demand. For this reason, strengthening and reinforcement solutions, consisting of materials with significant tensile strength applied to or embedded into the load-bearing masonry walls, are generally employed to cope with this deficiency. In this thesis, the equivalent-frame modeling (EFM) for masonry structures is first discussed, highlighting its advantages, assumptions, and limitations through comparison with experimental results of shake-table tests on masonry buildings and aggregates. Subsequently, a novel three-dimensional macroelement is proposed to couple the in-plane and out-of-plane response of masonry walls subjected to lateral loads, resorting to a computationally efficient sectional integration for the axial-flexural behavior. More specifically, the three-dimensional macroelement builds upon a pre-existing two-dimensional formulation, which allows to effectively and efficiently reproduce the nonlinear static and dynamic behavior of an unreinforced masonry panel with a limited number of degrees of freedom. Furthermore, taking advantage of the proposed three-dimensional formulation, additional lumped and distributed reinforcement is incorporated into the macroelement, enabling the explicit modeling of several reinforcing and strengthening layouts. The resulting formulation is finally validated against the experimental results of a quasi-static cyclic shear-compression test on a stone-masonry piers strengthened by composite-reinforced mortar (CRM) jacketing.