Strut-And-Tie Model for Predicting the Shear Capacity of Confined Masonry Walls With and Without Openings

Abstract eng:
The confined masonry structure consists of load bearing walls strengthened with nominally reinforced concrete elements at the perimeter and other key locations. The confined masonry system has evolved based on its satisfactory performance in past earthquakes and can be considered as one of the most suitable alternatives to seismically vulnerable unreinforced masonry system due to its similar construction practice and economic feasibility. However, the existing analytical models for estimating the design shear capacity of confined masonry walls are primarily semi-empirical equations which are based on either friction theory or elementary theory of elasticity. These analytical equations are either highly influenced by the formulae originally developed for unreinforced and reinforced masonry walls or are based on the limited number of laboratory tests. The inconsistent predictions of in-plane shear strength by these existing models necessitate the development of a rational design method for confined masonry walls, especially with openings. Strut-and-tie model has evolved as the most useful method for shear critical structures and disturbed regions (often called as D-region) in concrete structures. This method provides a rational and consistent design approach by idealizing the structural member with appropriate truss models. However, a prior knowledge of flow of stresses is required to develop strut-and-tie model for complex structural members, such as confined masonry walls with openings. Thus, initially nonlinear finite element analyses were performed on confined masonry walls which satisfactorily simulated their lateral load-deformation behavior and failure pattern. The principal stress vector diagrams obtained from the FE analyses were used to develop strutand-tie models for confined masonry walls with and without openings. These strut-and-tie models provided an insight on how to construct the network of struts and ties for complex cases particularly in walls with openings surrounded with confining elements. With few simplifying assumptions, strut-and-tie models consistently provided good predictions for the in-plane strength of confined masonry walls within an error of 15% when compared to the experimental results. Due to its simplicity and reliability, the strut-and-tie model can be put into practice for the analysis and design of single to multi-storey confined masonry buildings.

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