Improving the lateral load resistance of vernacular masonry walls subject to flooding

Abstract

Low-rise vernacular masonry buildings are vulnerable to damage from extreme flooding. This paper presents findings from a study based in Sri Lanka assessing the structural resilience of non-engineered single-storey houses constructed with either fired clay brickwork or cement block masonry walls. A structural survey of flood-damaged houses enabled characterisation of masonry materials, and development of proposals to improve the lateral load capacity of masonry walls. The structural survey revealed that a combination of low-quality masonry units and variable thickness of mortar beds may have contributed to flexural failure due to the hydrostatic pressures during flood events. An experimental programme investigated the impact of differing masonry units and mortar thickness on masonry properties under dry and saturated conditions. A simple retrofit method has been developed, using reinforced renders, that enhances sectional flexural capacity by over 11 times, offering greater resilience to lateral flood loads. The impact of this research study will have direct welfare benefits for Sri Lankan people living in flood-risk areas, reducing the risk of structural collapse and enabling people to remain safely in their homes during flood events.

Retrofitting and rehabilitation of vernacular housing in flood prone areas in Sri Lanka

“…Simple methods of reinforcing such walls using geogrid reinforced plaster coats were developed and the potential improvement in wall capacity quantified. The study presented in this paper expands on this previous research [Platt et al, 2020], utilizing wire mesh and including the characterisation of constituent materials and single leaf panels (approximately 390 -500 mm x 500 -550 mm (W x H)).…”

“…In 2018, field surveys of flood damaged regions were carried out by the University of Moratuwa (UoM) and the Sri Lankan Government National Building Research Organisation (NBRO) [Platt et al, 2020]. The southwestern Kalutara, Matara, and Galle regions, having a combined total population of 3.1 million (2012 census), was selected to provide context to the need for intervention.…”

“…A PVC coated steel wire mesh, (widely available from local building supply stores) was previously investigated in a pilot study by Platt et al (2020) and is presented here for comparison. The square mesh, normally used as a lightweight material for a variety of domestic uses, was selected for its low cost and availability.…”

“…In response to flood events, retrofitted buildings are thought of as either flood resilient or flood resistant [Platt et al, 2020]. Flood resilience permits intrusion or contact with the flood water during events, but without permanent structural damage, although normal building occupancy may be affected.…”

“…URM structures are usually plastered and rendered single leaf construction; with the coatings improving resistance to moisture ingress as well as aesthetics. In Sri Lanka, plaster and renders are commonly 1:5 cement: sand mixtures applied in one or two coats totalling 15-20 mm [Platt et al, 2020]. Although reinforcing plaster and render coatings is currently not common in Sri Lankan practice, there is scope for inclusion of reinforcement into the plaster, with potential to greatly improving the flexural capacity of walls.…”