Confined masonry for seismically resilient low-cost housing in India : a design and analysis method

Abstract

Confined masonry (CM) is a viable housing typology that is resilient and economical for developing countries in seismic regions. Given its suitability for low-tech environments, multiple authors have published instructions on CM construction that do not require engineering knowledge. As a result these guidelines impose constrictive design requirements. Analysis methods exist for calculating the stress demand on shear walls of a CM building under earthquake loads which may be applied to any design, but they require technical expertise to perform. A procedure for designing confined masonry buildings is presented that employs a combination of seismic analysis techniques to take into account torsional effects and allow for complex designs while requiring low computational effort. Parametric studies are performed on this procedure which show reliable, conservative structural design outputs. Confined masonry is a structural wall system, therefore its seismic resilience depends on the wall shear strength, which is related to the compressive strength of the masonry. In India bricks used to build homes are often of poor compressive strength, even lower than the minimum allowed by the Indian masonry code, which is lower than that prescribed in other international standards. Experimentation was conducted on the strength of masonry in Gujarat, India to investigate the effect of varying mortar qualities when low strength bricks are used. With average brick strengths below 2.5 MPa a mud mortar with no cement and a 1:8 cement:sand ratio mortar resulted in approximately 41% and 21% higher prism strengths, respectively, than a 1:6 cement:sand ratio mortar. This shows that a mortar with less cement would save cost and result in a more resilient structure when building with bricks of this strength. Observations and hypotheses are presented for this behavior, but larger scale testing is recommended to better understand this outcome and inform better building practices that can save lives and money.