Drift Capacity of Urm Walls: Are Analytical Models an Alternative to Empirical Approaches?

Code design of unreinforced masonry (URM) brick buildings is based on elastic analysis, which requires as input, among others, estimates of the in-plane drift capacity at the considered limit states. Current approaches assess the drift capacity of URM walls by means of empirical models with most codes relating the drift capacity to the failure mode and wall slenderness. Comparisons with experimental results show that such relationships result in large scatter and do not provide satisfactory predictions. The objective of this paper is to investigate whether analytical models could lead to more reliable estimates of the displacement capacity. The drift capacity is investigated using a recently developed analytical model for the prediction of the ultimate drift capacity for both shear and flexure dominated URM walls. The approach is loosely based on plastic hinge models for reinforced concrete or steel structures. It takes the influence of toe crushing in URM walls explicitly into account as along with geometric and loading conditions. It is part of a more comprehensive model describing the whole force-displacement response of URM walls failing in shear or flexure. This paper summarises the key features of this analytical drift capacity model and benchmarks its performance against a data set of 34 full scale wall tests. It shows that the analytical model yields significantly better estimates than empirical models in current codes. The paper concludes with an investigation of the sensitivity of the ultimate drift capacity to the wall geometry, static and kinematic boundary conditions by means of parametric studies.