On the Out-of-Plane Strength of Masonry Infills Encased in RC Frames

With reference to the widespread out-of-plane (OOP) failures of infill walls in reinforced concrete (RC) buildings during the 6 February 2023 earthquakes in Kahramanmaraş, Turkey, this paper investigates the OOP strength of unreinforced masonry (URM) infills without openings, enclosed in RC frames, while also considering the effect of prior in-plane (IP) loading. A comprehensive database has been compiled, including all available tests on infills subjected to OOP loading and sequential IP–OOP loading, as well as those on infills with gaps between the RC frame and the masonry panel. This study evaluates the effectiveness of established design models at predicting the OOP strength of infills in RC frames and proposes refinements to improve the predictive accuracy. For the OOP strength, two arch-based models are applied, and the impact of prior IP loading is addressed through a reduction factor, R. Based on test observations showing that prior IP loading disproportionately reduces the OOP strength in vulnerable infills, an improved R-factor is introduced, providing better alignment with experimental results than four existing design formulas. The influence of gaps between the infill and RC frame on the OOP behavior is also examined. The findings reveal inconsistencies and reduced reliability among the available design models, highlighting the need for further research on this critical topic.