Earthquake protection for poor people’s houses
Practical Action
Improving stone masonry
In the Near East, the reinforcement of masonry has much improved the performance of stone.
The materials used for reinforcement are concrete or timber, the latter being far cheaper.
Horizontal tie-beams are essential, and they can be combined with a vertical frame, and, in the
case of timber, diagonal bracing.
Horizontal tie-beams should appear at roof level, above windows and doors, and sometimes also
below windows and on top of the foundations. Full frames are an expensive way of reinforcing a
building. It is more affordable, but also more risky, to reinforce only the high-stress areas – near
openings, corners or intersections – with shorter pieces of timber or steel.
A better quality of materials also increases resistance. Round stones should be avoided; angular
stones, preferably dressed, will considerably improve the internal bond in a wall. The use of
flatter stones, such as slate, will help as well, as long as they are placed flat, not on their side.
Better mortars increase the bonding, which is particularly important for corners and intersections
and around openings. Wherever available and affordable, the use of cement, lime pozzolana,
lime or gypsum mortar (in that order of preference) should be encouraged. (A pozzolana is a
substance which, when mixed with lime and water, hardens as a cement.)
A high level of construction quality is important, particularly to improve bonding and therefore
resistance to movement. The practice of building double- faced walls, without tie stones and
with rubble infill should be strictly avoided. Stones should always be placed as flat as possible,
and dressed whenever needed to fit specific gaps, rather than using large quantities of mortar
and small stones to fill up voids. Vertical joints should be staggered so that large vertical cracks
do not occur. Masonry walls should occasionally have stones that reach through the entire
thickness of the wall ('through-stones',) which perform the same tying functions as the dowels
(steel or wooden connecting pieces). Finally, walls should be neither too thin, which makes good
masonry patterns very hard to realize, nor too thick, since that would unnecessarily increase the
mass. A reasonable thickness for masonry with irregularly shaped stones is in the order of 40 to
50cm.
Figure 3
Figure 4
Adobe masonry
For adobe reinforcement often provides the biggest improvement to the masonry. A continuous
ring-beam is very desirable, particularly at roof level; it helps to tie the tops of the walls together
and provides a fixed base for the roof. Continuity can be ensured by lapping the reinforcement or
splicing the timber. If there are many openings, or if walls are greater than 2.5m in height, a
similar ring-beam at lintel level is recommended. If unable to resist great lateral forces
themselves, walls may still move sideways during earthquakes, unless vertical reinforcement is
added to tie them to the foundations and to increase bending resistance. Vertical reinforcement
is particularly useful in high-stress areas: at corners or intersections of walls and along openings.
A picture of an ideal combination of reinforcement is shown in Figure 2.
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