A numerical insight into the reliability of seismic strength models for masonry piers and spandrels

With the aim to provide an insight on the effectiveness of existing formulae for the flexural and shear strength of masonry piers and spandrels, this paper reports and compares results obtained from pushover analyses performed on a set of plane masonry walls. As reference, the formulae provided by the Italian Building Code (IBC) were considered. Nonetheless, the formulations provided by IBC are similar to the ones reported in the Eurocode Standards (ES), and thus conclusions of this paper can be extended to the latter. Three types of masonry walls were considered which differ in the span-to-height ratio b/h of the masonry beams, namely: a) slender beams (b/h = 2.0); b) intermediate beams (b/h = 1.00) and c) short beams (b/h = 0.75). For each masonry wall, the unreinforced configuration (URS) was compared with two resisting schemes: concrete ring beams (RSB) and steel chains (RSC). Therefore, a total of 9 types of masonry walls were considered which differ in terms of geometry and resistance mechanisms. To perform the pushover analyses, the finite element technique was employed by using three different load distributions. The results expressed in terms of inner forces on the piers and spandrels were subsequently compared with the formulae for flexural and shear strength provided by IBC. The comparisons showed that the reliability of these equations is at least questionable, especially for the prediction of the spandrels’ strength. In this case, the strength models provided by the Standards underestimate by a large amount the real strength both for the unreinforced and the strengthened walls, especially in the case of slender spandrels in strengthened walls.