|Corporal Damage as Related to Building Structure and Design: The Need for an International Survey (Centre for Research on the Epidemiology of Disasters, 1989, 16 p.)|
Anti-seismic building aims at modifying the interaction between the habitat and its occupants. It is reported to be most effective at least in saving lives and preventing casualties, provided the building codes are actually adhered to. It is reported that in Japan, the number of deaths due to earthquakes has steadily decreased since the ediction of the Disaster Countermeasures Basic Act in 1966. Time series however are generally not matched for the number and magnitude of earthquakes.
Anti-seismic building techniques have made tremendous progress over the last few decades. Buildings of 50 or more stories sheltering thousands of people are build in highly hazardous areas. They are reputed safe in case of earthquakes of high magnitude. Anti-seismic design have been tested through computer simulation, on mechanical models, and to some extent, in real life situations. The experience of Mexico City, 1985, has clearly demonstrated that such buildings, when the coding codes are applied, can resist an earthquake of magnitude 8.4.
That is a remarkable achievement. One may however wonder whether the primary purpose of these engineering developments is to protect people, or rather to overcome the challenge of pursuing the necessary modernization of very large cities which happen to be constructed in hazardous areas. Thus, whereas there is no doubt that anti-seismic design confers protection on an individual building basis, what the protection is in terms of population-coverage remains questionable.
Three types of situations should be considered:
(1) The enforcement of anti-seismic building code should be enforced for all new structures, especially public facilities, offices spaces and housing, in earthquake prone areas. Can it be afforded everywhere, especially in poor countries, while it is known to increase the building cost by 10 or 15 percent ? Often, antiseismic building measures are enforced for the reconstruction of a town which has suffered a recent earthquake or has been repeteadly destroyed in the past. There is no guarantee however that the next earthquake will occur at the same place (although it may be the case as in Orlsville/El Asnam, Algeria, 1954 and 1980). One would like to know, world-wide, and by country or disaster-prone areas, (a) the proportion of people who are effectively protected at the moment by anti-seismic buildings, both at home and in the working place; (b) what would be the cost to afford complete protection. One could of course conceive of a scheme which should make foreign loans or grants conditional to the implementation of anti-seismic measures, on the model of what is now recommended for environmental protection. This conditionality is however pure anathema for a number of developing countries. In conclusion, in many places, in the next future, anti-seismic building will be reserved to a limited number of major buildings, the more the better.
(2) In most earthquake exposed cities, structures, modern or ancient, built with no antiseismic techniques whatever, represent the majority. Antiseismic fitting of old buildings raise additional issues. Beyond the cost, the mere number of buildings to be renovated may require setting priority, which in turn could lead to delicate ethical and political choices.
What about the existing old houses? Should they be renovated, destroyed, replaced? The question is particularly relevant for the Mediterranean countries. Cost of renovation for making them anti-seismic would be considerable. It could be carried out on an individual basis, and probably not on a large scale.
The most extreme irremediable situation consists of those buildings which are supposed to be antiseismic while actually the antiseismic codes were not adhered to.
(3) The earthquake resilience of traditional housing varies according to the style and shows large geographical variations. In most developing countries, traditional housing is gradually replaced by new styles. The study conducted by R. Glass in Santa Maria Cauque, Guatemala, following the 1976 earthquake, provides a well-documented example of the relationship between deaths and casualties and the type of housing (1). In a 1918 earthquake, at a time when all houses were built of cornstalk and mud-covered, no death occurred. The first adobe houses, with dried bricks held by weak mud mortar, were built around 1925. In 1971, 85 percent of the houses were built in adobe. In the 1976 earthquake, 5 per cent of the village's population were killed. Clearly, in 50 years, the risk of quake-related trauma has gone from minimal to maximum.
The unregulated wild mix of traditional building methods and new materials is a characteristic of economic development in poor countries. In Turkey, people are extending their houses by building additional floors, placing a large concrete slab on insufficiently supported walls. Such procedure is calling for disaster at the first tremor.
The problem is an usual one not dissimilar to the Green Revolution in which irrigation without proper sanitary engineering brings water borne diseases, and insecticide poisoning is the price paid to protect the crops. Introduction of new technologies must go together with corresponding education as a package. For earthquake protection, it calls for research on the housing factors as related to traumas, in view of edicting simple minimal building codes at no or minimal cost, and education at the community level.
One conclusion is that, whatever the great success achieved in anti-seismic design, in many areas, emergency and rescue will most likely remain a prime component of disaster management.