Mitigating damages to infill walls under combined in-plane and out-of-plane loadings using a spider web-inspired strengthening strategy: Numerical analyses

Unreinforced masonry walls (IMW) are commonly used as infills to envelop and partition reinforced concrete (RC) frame buildings. These IMWs are non-loadbearing, however they contribute to the in-plane (IP) load resisting mechanism of the RC frames and are prone to out-of-plane (OOP) failure during lateral actions, such as earthquakes, impacts, tsunamis, and high winds. The OOP failure of IMWs is influenced by prior IP damage, and therefore the characteristics of bi-directional interaction (IP and OOP) should be accounted to assess the appropriate OOP capacity of IMWs in RC frames. However, limited studies have been reported on the bi-directional failure characteristics of IMWs, especially mitigation of this failure and increasing the OOP capacity of the walls without increasing the stiffness in the IP direction. In this research study, finite element (FE) based numerical models of IMWs under bi-directional loadings has been developed and validated using existing experimental data. Numerical and experimental results show good agreement of failure modes and both IP and OOP load-displacement characteristics. To mitigate their failure, a nature inspired spider-web grid (as a surface rending strengthening system) was applied to the IMWs and their IP and OOP responses were evaluated numerically. Using spider-web-inspired reinforcement on the rear face of the IMWs yielded a 31 % increase in their out-of-plane capacity with an increase in out-of-plane displacement by 2.7 times compared to the unreinforced IMW configuration. Findings of this paper will help to improve the designs of IMWs vulnerable to combined IP and OOP loadings.