Earthquake protection for poor people’s houses
Practical Action
Mud and pole construction is a method that occurs independently in many developing countries.
It consists of a round pole frame which was set directly into the ground, infilled with smaller
wooden poles and interwoven to form a matrix which is then plastered with one or more layers of
earth. Timber buildings in a seismic area usually fare better in an earthquake due to the
flexibility of the material and the buildings and their light weight compared to concrete or steel.
Weaknesses in this type of construction lie in the weakening of the timber poles due to rot,
insect and fungal attack, and often in poor connections in the timber frame. Deterioration of the
frame can be avoided by preventing exposure of the timber poles to moisture by using
preservative treatment and preventing contact with the soil moisture at foundation level.
In Peru, this type of construction is known as quincha. Many heritage earthen buildings higher
than one storey usually have a lighter second storey constructed in quincha in response to the
1746 earthquake in Lima. Some newly constructed adobe buildings designed to be seismically
resistant have also included a second storey made of quincha. It significantly reduces the mass
of the second storey and attracts less seismic forces on the building.
Some design guidelines
The study of the performance of buildings during earthquakes tells us something about the
relative resistance of various building technologies. Even with the same technologies, however,
we often notice variations, caused by other factors, such as the design or location. Improvements
to the technologies would be less effective if these factors were not taken into account. Some
major guidelines are:
Carry out a site investigation;
Select a solid site; avoid landfills, flood plains, drainage paths and steep slopes;
Position the foundations on rock or firm soil, avoid stepped foundations;
Design compact buildings with a symmetrical shape and closely spaced walls in both
directions. If that cannot be done, design them in separate, regular blocks;
Build one-storey houses where possible;
If buildings have more than one floor, opt for similar floor shapes and designs;
Separate adjacent small buildings by at least 75 mm;
Make walls light to reduce the horizontal forces caused by earthquakes;
Walls should not exceed 3.5m in height, unsupported lengths of wall should not exceed
7m;
Make roofs light to avoid them pushing walls sideways and falling-in on people;
Avoid gables, they may fall inwards;
Avoid long walls without intermediate support and tie walls together at the top
Keep openings to a minimum, well distributed over the building and within walls; keep
them centrally positioned, at least 60 cm away from the inside of corners and
intersections and from the nearest other opening.
Openings should not be wider than 1.2m and bearings of lintels should be at least
500mm either side of the opening;
Provide strong joints between structural components; use a ring beam and a plinth beam
where possible; use bracing at corners;
If masonry walls are used, create good bond especially at corners and intersections;
If concrete pillars are used, lap vertical reinforcements mid way between floors and not
just above floors;
Control the quality of the materials used.
Improve the workmanship, particularly in mortar preparation, masonry and connections.
For an illustrated guide of the above points and more useful advice on good practice, the
Earthquake Reconstruction and Rehabilitation Authority in Pakistan have published a guidelines
document.
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