A novel approach for the estimation of seismic drift capacity in unreinforced masonry (URM) shear walls based on governing structural parameters

Abstract The implementation of displacement-based verification in the second generation of Eurocode 8 requires a consistent definition of the seismic drift capacity of unreinforced masonry (URM) shear walls. Current codified approaches assign drift limits according to predefined failure modes. However, experimental evidence indicates that drift capacity is governed by the coupled effects of axial load ratio, wall slenderness, and moment distribution, resulting in gradual transitions between shear-, hybrid-, and flexure-dominated response mechanisms that cannot be adequately represented by a failure-mode-based framework. This study presents a mechanically transparent and statistically calibrated formulation for the drift capacity of URM shear walls. The proposed approach is derived from a comprehensive numerical simulation matrix covering a wide range of axial load ratios, wall geometries, and boundary conditions, and is subsequently validated against the extended Modern Masonry Shear-wall DataBase ([MoMaS-DB 2026]) comprising cyclic shear-wall tests. A normalized shear slenderness parameter is introduced to consistently capture the governing interaction effects. Drift capacities are calibrated using an unbiased lognormal regression procedure in linear space, ensuring statistical consistency without artificial regularization. The results demonstrate a continuous increase in drift capacity with increasing normalized shear slenderness, reflecting the progressive transition from shear-dominated to flexure-dominated behaviour. Unlike conventional failure-mode-based formulations, the proposed approach avoids discontinuities and provides robust predictions across a broad range of boundary conditions. The method has been incorporated as an alternative procedure in FprEN 1998-1-2 (2025), thereby supporting the advancement of performance-based seismic design of masonry structures.