Search

Reinforced concrete (RC) frame structures infilled with clay masonry walls represent a common construction practice worldwide. However, the significant interaction between in-plane (IP) and out-of-plane (OOP) response of the infill walls, and their brittle behaviour, can increase the seismic vulnerability of the building to both local and global mechanisms. Therefore, it is necessary to develop adequate tools to assess the seismic performance of infill panels. To this end, this paper presents a new macro-model for evaluating the IP/OOP behaviour of infill walls. The model consists of four strut elements, two for each diagonal of the wall, and two equal OOP masses placed in the centre of the panel; each strut is made of two beam-column elements that allow for the creation of a plastic hinge at the mid-span, where the non-linearity due to the IP/OOP interaction is concentrated and modelled through a nonlinear fibre section. The model is experimentally calibrated for four types of thin clay masonry panels, one unreinforced and three strengthened. To show the potential of the new infill model, a non-linear static analysis procedure is proposed for evaluating the lateral response of RC infilled frames. This simplified procedure is finally used in a parametric study that analyses various types of infilled frames. The results demonstrate the effectiveness of the proposed model, as well as of the strengthening solutions adopted to mitigate the IP/OOP interaction effects.

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.