Simple and Effective Seismic Retrofit Techniques for Low-Strength Masonry Buildings

Although earthquakes over historic time have destroyed uncountable numbers of low-strength masonry (adobe), rural dwellings, killing and injuring hundreds of thousands people, it’s only been in the last three decades that engineers and architects have begun to investigate the types of damage and to develop simple cost-effective techniques of reinforcing these buildings in order to mitigate the great risks to the millions of people who currently live in these types of dwellings. It is generally assumed that adobe structures are highly vulnerable to earthquake shaking. However, it has been observed that specific types of damage can be expected to occur, and that these types of damage can and need to be addressed by simple, yet effective retrofit techniques in order to mitigate dwelling collapse.

Field studies of seismic performance of adobe buildings have now been carried out in several countries, including: Peru, Mexico and other Latin American countries, the U.S., and Iran. In addition, several shake-table tests of adobe structural models have been conducted in Peru, Australia, the U.S., and Iran, and have duplicated several of the types of damage observed in the field. These tests have also been used to study the efficacy of different reinforcing measures, generally known as stability-based retrofit techniques. The principle goals of stability-based retrofit systems are to:

1.            Ensure structural continuity of the walls by installing a bond beam, tie rods, a diaphragm, or some type of continuity hardware at the top of the walls;

2.            Prevent out-of-plane overturning of walls with either horizontal or vertical straps, or surface mesh interconnected with the top-of-wall continuity hardware;

3.            Limit relative displacement across cracks or potential cracks in the walls by thru-wall ties interconnected to the horizontal and vertical straps, or the surface mesh.

Stability-based retrofit techniques promise to provide simple and effective life-safety measures for mitigating the vast number of deaths and injuries related to damage and collapse of rural adobe dwellings during seismic events.