Earthquake protection for poor people’s houses
Any effort that helps to reduce the vulnerability of poor people to disasters, and thereby also
reduce casualties and future economic losses, is worthwhile in itself. As in the area of medicine,
where money spent on the prevention of a disease reduces the amount required for its cure, so
aid agencies as well as local governments should spend larger parts of their disaster budgets on
reducing vulnerability instead of on relief. If one looks at the factors listed earlier, it becomes
clear that only long-term development work will considerably reduce vulnerability: if poor people
gain more resources and more power they will become less vulnerable. And it often does not
need large sums to get this process going, as Andrew Maskrey describes in his excellent book
Disaster Mitigation – a community based approach.
Better technologies are needed to reduce the vulnerability to earthquakes of the housing of low-
income groups, but we cannot impose such technologies upon people. The approach that most
developing countries have attempted is simply to adopt a set of standards and regulations with
respect to the earthquake resistance of buildings which are directly derived from the ones used
in the USA, Britain or France. They usually prescribe reinforced-concrete frames or some other
technology that is unaffordable by the poor, and like other standards, they have been ignored by
the poor. Engineers should learn not to aim for the ideal solution, but for the affordable and
appropriate solution; they have to allow a higher level of risk than standards usually permit, and
they may have to set priorities.
An example of such a priority might be the prevention of casualties as a result of roof collapse,
and some engineers have actually designed separate roof-supporting systems, accepting that if
masonry walls fall down, they can be rebuilt afterwards.
The best approach to increasing earthquake resistance is usually to learn from the earthquake
performance of dwellings in a given area, noticing problem areas and sometimes better
technologies, and then to use mainly local resources for further improvement. The rest of this
article gives some examples of improvements to three types of construction: stone masonry,
adobe masonry and quincha.
Earthquakes make buildings shake; the resulting lateral forces are determined by the mass of the
building. Dwellings with heavy walls and roofs therefore run the greatest risks, and these are very
common in the major earthquake belts that encircle our globe, such as Central and South
America, the Mediterranean, the Near East and China.
Heavy walls may be damaged as a result of:
shear stress, caused by forces parallel to the plane of the wall, and resulting in diagonal
cracks developing in high-stress areas, such as corners, intersections or openings;
forces perpendicular to the wall, causing bending out of plane;
a combination of these two stresses.
Random stone masonry, which occurs widely in the Mediterranean and the Near East, is very
dangerous in earthquakes. These walls lack internal cohesion and even disintegrate during
moderate earthquakes; this has happened during earthquakes in Lice, Turkey; in Yemen; in
Pakistan; and in Iran.
Adobe, or soil-block masonry, is even more common in poor people's housing. The cohesion and
the tensile strength of adobe walls are often insufficient to resist even a moderate earthquake:
walls shear apart in high-stress areas; they incline and are pushed outwards by the roof, which
then may fall on the inhabitants. Adobe structures have contributed most to the number of
earthquake casualties, particularly in Latin America, the Near East and China. Bad performance
has often been caused by such factors as poor adobe quality, poor bonding and poor
workmanship, a lack of maintenance and the presence of humidity in the walls.