Out-of-plane behavior of U-shaped unreinforced masonry structures

The out-of-plane behavior of masonry walls is an important aspect of their response, particularly in seismic regions. While previous studies have examined various geometries and materials, there exists a dearth of research on U-shaped walls, specifically with diverse geometric configurations. Moreover, the influence of axial load on out-of-plane behavior remains largely unexplored, limiting practical applications. This study aims to bridge these gaps by comprehensively investigating the out-of-plane behavior of U-shaped walls, focusing on the quantification of variable parameters encompassing geometry and axial load. A three-dimensional finite element model using the macro-modeling approach is used to analyze the structural response of U-shaped masonry walls under out-of-plane loading. The accuracy of the numerical modeling approach has been validated by available experimental test results to demonstrate the effectiveness of the modeling approach in predicting the out-of-plane behavior of U-shaped masonry structures. Subsequently, a series of parametric studies delves into the impacts of distinct geometrical attributes, including thickness, height, and span size, shedding light on the behavior of these walls across diverse geometric configurations. The results indicate that the capacity of the wall at the connection between out-of-plane and cross walls significantly influences the overall behavior and the failure mode. It was found that axial load substantially increases the strength of walls, in order of 1.5-3 times, and the positive effect of axial load was more significant than the secondary effects in most cases, though the significance of secondary effect drastically increases by increasing the height. It is shown that walls with longer span have much better behavior in the presence of axial load. Based on the results, for each specific geometrical parameter, a linear function can be considered for relation between strength and axial load. These findings can provide useful insights for the design and analysis of U-shaped masonry structures, particularly in seismic regions where out-of-plane behavior is a critical factor in their performance.