Studies on Con ned Masonry Building

Abstract

Brick masonry building construction is a common typology adopted worldwide due to flexibility offered to accommodate itself to changing environmental conditions. Brick masonry building otherwise performing well under gravity loads shows low resistance against lateral loads induced due to an earthquake and thus it suffers heavy damage. Concept of Confined Masonry (CM) building is gaining popularity amongst engineering community as it offers good lateral resistance due to presence of confining elements. Recently, few residential and office buildings have been constructed using confining elements in India and other parts of the world. Few literature in terms of guidelines and technical reports are available to understand the confined masonry buildings. Dynamic behaviour of confined masonry building under seismic excitations is not explored yet. Model testing of scaled confined masonry building is also not explored to understand its behaviour under dynamic loading. The present study aims to perform analysis and design of conventional masonry building and improve its lateral load resistance by designing as confined masonry building. A three storeyed realistic residential conventional masonry building is considered in highest seismic zone-V as defined in IS:1893(Part-I)-2016. It is analyzed and designed for gravity and lateral loads following IS:4326-2013 codal stipulations and safety of each walls is assessed. Same building is converted to confined masonry building by introducing Reinforced Concrete (RC) elements; Tie-columns and Tie-beams. Analysis and design of confined masonry building is carried out following draft code BIS: CED-39. Design of RC elements of CM building is performed through Limit State Method. Wall stiffness and wall density for confined masonry building were evaluated. Torsional stiffness of CM building is evaluated and was compared with conventional masonry building. Base shear values for CM building reduces by 2.37 times and 2.73 times in X- and Y- directions of the building, respectively as compared to conventional masonry building. It has been found that wall stiffness of CM building increases by 15% to 30% vis-a-vis conventional masonry building. Torsional stiffness is found to be increased by 1.66 times (66%) with respect to conventional masonry building. Mechanical properties of red clay brick units, cement mortar cubes and masonry prism are evaluated at Heavy Structures Laboratory (HSL) of the Civil Engineering Department. Three forms of mortar (Cement, Cement-Lime and Cement-Fly Ash) are explored to study the impact of lime/fly ash addition in cement on strength of the mortar. It has been found that addition of lime in cement improves ultimate strain capacity of masonry prism. It was proposed to test scaled model of confined masonry building on unique shock table facility available at HSL. However, the said objective could not be achieved due to extraordinary situation of pandemic. In view of that, an attempt is made to develop computational model of confined masonry building, which can be used to study dynamic behaviour of the building. A dynamic analysis in the form of response spectrum or time history analysis may be performed to evaluate structural response of CM building.