Second-order effects in URM walls subjected to compression and out-of-plane bending: From numerical evaluation to proposal of design procedures

Although the load-bearing capacity of masonry walls has been receiving researchers’ attention since the 1950s both analytically and experimentally, in the scientific and technical community there is still heated debate on the actual methodology to adopt for the verification of URM walls subjected to eccentrically loaded walls, considering second-order effects. Moreover, it is still not well recognised that safety checks on structural walls subjected to significant lateral (e.g. seismic) actions require to be verified in terms of lateral flexural capacity and that buckling effects also need to be properly considered in these cases. To date, possible design procedures for evaluating second-order effects in strength verification of walls are based on axial load and moment capacity reduction factors, here respectively called ϕm and ϕM. This paper offers a refinement of the numerical calculations of ϕm and ϕM, leading to polynomial-type models and analytical formulations that improve accuracy in evaluating both factors. Moreover, it has analytically and numerically been demonstrated that there is a one-to-one correspondence between the two reduction factors ϕ, since they represent two ways of characterising the same effect. The results on the reduction factors are finally compared with those from past experimental campaigns and from some standards and can serve as reference for codified procedures.