Effective stiffness of unreinforced brick masonry walls

Code design of Unreinforced Masonry (URM) buildings is based on elastic analysis, which requires as input parameter the effective stiffness of URM walls. Current approaches estimate the effective stiffness as fixed ratio of the gross sectional stiffness but comparisons with experimental results have shown that this does not yield satisfactory predictions. In this paper, a recently developed analytical model for the force-displacement response of URM walls is used to investigate the effective stiffness. First, the key features of this model are summarised. In further course, the model is used to predict the effective stiffness of full-scale tests on modern unreinforced clay brick masonry walls and the results are compared to the provisions of Eurocode 8. Concluding, the model is used to investigate the sensitivity of the effective stiffness to the wall geometry and axial loading. strongly non-linear load-displacement histories by means of bi-linear curves (Fig. 1). One input parameter for the construction of these curves is, again, the effective stiffness (kef). When determining the effective stiffness from experimental results on shear-compression tests, it is typically defined as the secant stiffness of the system at 70% the peak shear load, e.g. Penna et al. (2014), Frumento et al. (2009). Comparison to fullscale wall tests in Sect. 3 shows that EC8 underestimates this effective stiffness. Furthermore, estimating the effective stiffness as a fixed percentage of the gross sectional stiffness means that the forces are effectively distributed proportional to the gross sectional stiffness. Such an approach does not account for the fact that the extent of cracking