Introduction

Earthquakes can be the single most devastating natural event, with many lives claimed due to the failure of residential buildings. Whilst there are many building codes and guidelines for building back better to create new, seismic resistant buildings, this option may not be affordable to all whose houses remain standing, but are still at risk of experiencing an earthquake.

Damage types in unreinforced masonry

Unreinforced masonry, whether it is made of stone, adobe bricks, or fired bricks, is a widely used method of building in many developing countries. The methods of retrofitting will focus on these types of buildings as they are most commonly the homes of people who would require affordable retrofit solutions. However, slightly more intrusive, and therefore potentially expensive methods will also be included to give an idea of the possibilities available.

Walls will experience different modes of failure depending on their orientation to the earthquake movement. Parallel to the ground movement, walls will experience shear and cracks will form in a diagonal fashion. The cracks form an X-shape because shear will be experienced in both directions to follow the ground movement. Diagonal cracks also form from the corners of openings since there stresses are highly concentrated here. Vertical cracks are formed at the middle of walls perpendicular to the ground movement, as this is the location of high bending stresses, as are ends where adjacent walls are attached. Cracking here can lead to separation of the walls at corners. Cracks can propagate and result in sections of the wall falling away and partially collapsing. In some instances, corners, sections of wall or entire walls can fall out of plumb. Prolonged shaking can also lead to delamination, in which a layer of masonry may fall away from the wall, or bulging, where the wall face separates and creates an area of thick wall. Depending on the earthquake intensity and duration, extensive damage can lead to total collapse. It is imperative that inhabitants are able to escape before collapse happens.