EFFECT OF CROSS WALLS ON THE BEHAVIOR OF UNREINFORCED MASONRY WALLS

Abstract

Masonry has been the most commonly used construction material in the history of humankind. Some of the signi cant advantages of masonry structures are economics, simplicity, and ease of construction. It involves placing one masonry unit over the other, either with or without mortar. In India, a notable amount of buildings are made up of masonry. Masonry structures have su ered severe damage during past seismic events around the world. It has been observed that the buildings constructed as per the codal provisions have shown comparatively lesser damage than those constructed by following traditional practices without any earthquake-resistant features. Similar to concrete, masonry is also strong in compression but weak in tension. Because of masonry's lower tensile strength, its failure in both the in-plane and out-of-plane direction may lead to the total collapse of the structure. In order to reduce the damage in unreinforced masonry buildings, it is mandatory to follow various codal provisions. Masonry building constructed using earthquake-resistant features performs better because of its box action, in which most of the lateral loads are attracted toward the in-plane walls. The out-of-plane walls transfer the forces to the inplane walls by inertia action. It helps to minimize the damage in the out-of-plane direction. Indian Standards codes of practice, IS 4326:2013, suggest di erent types of mortars for buildings constructed in various seismic zones. The proportion of selected mortar type signi cantly impacts the behavior of the masonry walls. Therefore, the e ects of di erent types of mortar on masonry compression, tension, and shear strength have been studied experimentally by following the provisions mentioned in the relevant Indian codes and ASTM standards. A total of seven types of mortar constituents have been considered in the study. The e ect of mortar on compressive strength is examined by carrying out the prism tests. The tensile bond test has been carried out to obtain the tensile strength, while the triplet test has been performed for shear strength. This study aims to nd the optimum proportion of lime, which bene ts masonry's compression, tension, and shear strength. The behavior of the masonry walls has been studied in the past by considering the rectangular shape only. However, in masonry buildings, walls are interconnected at corners and other locations. It makes the masonry walls of composite sections such as I shape, T shape, H shape, C shape, L shape, etc. The cross walls connected to the main walls considerably in uence the walls' strength, sti ness, and ductility. Therefore, a parametric study has been performed to investigate the e ect of anges on the in-plane behavior of masonry walls incorporating varying pre-compression, aspect ratio, and material strength. The material strengths range from poor to strong, while pre-compression of low, intermediate, and high magnitudes have been considered. Aspect ratios vary so that they represent both squat and slender type walls. The walls have been modeled using the simpli ed micromodeling approach in the nite element software Abaqus because of its reasonably better accuracy in the analysis. Bricks are modeled using the concrete damage plasticity model (CDP), and mortar is modeled using zero-thickness interface elements. During earthquakes, masonry walls are subjected to simultaneous in-plane and out-ofplane loadings. The box action in the masonry buildings ensures primary damage under in-plane loading. However, the walls that fail under in-plane loading are also subjected to a certain amount of out-of-plane forces. So, the e ect of out-of-plane loading on the in-plane strength of masonry walls has been investigated. Numerical simulation has been carried out for masonry walls of various shapes, considering varying aspect ratios and pre-compressions. Further, interaction curves have been developed by subjecting the out-of-plane loading to the walls, followed by in-plane loading until failure. A simpli ed procedure has also been suggested to use these curves for design purposes. Walls in masonry buildings are usually pierced by door and window openings. The presence of openings reduces the e ective area of the walls to resist gravity as well as seismic loads. The walls that are damaged severely under in-plane loading during the earthquake are also subjected to out-of-plane forces. Therefore, nding the out-of-plane strength of walls damaged by the in-plane load is necessary. So, this portion of the study is divided into two parts, (i) the e ect of various types of openings on the in-plane strength of walls and (ii) the e ect of in-plane damage on the out-of-plane strength of walls with openings. The in uence of in-plane damage on the out-of-plane strength has been investigated considering the walls with various types of openings and boundary conditions for rectangular, and I shape walls incorporating varying pre-compression. Masonry walls with door openings, window openings, and a combination of both have been considered herein. The interaction curves have also been developed for masonry walls with openings subjected to combined loadings.