New Challenges in Seismic Design - Earthquake Engineering for Structural Design - page 9

- Developing countries (less developed, economically weak, under-
developed countries), for which GDP per capita is less than $5000 US.
This framing is also related to the specific seismic problems of a country belonging
to the above classification.
Ninety percent of the world's major disasters in during 1990-1999 were in
developing countries. However, these countries have made fewer efforts than
developed countries to adapt their physical environments to mitigate the impact of
disasters or to insure themselves against disaster risk (Freeman et al, 2003).
In the recent decades, the seismic disaster risk in urban centers in both
developed and developing countries is increased. The seismic problems in
developed countries are related to the increasing of urban system and population,
whereas in developing countries the main source of increasing seismic risk can be
attributed to the overcrowding of cities with non-engineered buildings, inadequate
infrastructures and services, together with environmental degradation (Erdik,
1996). It is, therefore, clear that the tasks for the mitigation of seismic risk are
different according to the two situations (Fig. 1.3).
For Developed Countries, in spite of the improvement of code provisions, the
costs of losses due to earthquakes continue to increase, also under the condition
that the average magnitude of earthquakes remains approximately constant. The
maximum economical losses are produced when strong earthquakes happen near
big and modern cities. The number of fatalities is nevertheless reduced, because
new buildings are erected respecting the anti-seismic rules, having as a main
purpose the protection of life. Therefore, the main problems of developed countries
are economical.
Today there is an increasing number of people and buildings in earthquake-
prone areas, meaning that earthquakes affect more and more buildings, facilities,
roads, bridges, dams, etc., each year. Over half of the world population is
concentrated in urban areas covering just 4 percent of the world surface. Rapid
urbanization is a distinctive feature of world development and the number of mega-
cities will increase in future. As shown in the previous section, many of these cities
are situated in seismically active areas where the concentration of people continues
to grow and the damage produced during previous earthquakes is expected to be
magnified during the next seismic events. Therefore, one of the most important
lessons after an earthquake is the awareness to improve the seismic design
conception, in order to reduce the economical consequences of future important
earthquakes. The revisions of existing code provisions towards performance-based
design needs are suggested to be a proper way.
On the other hand, in the Developing Countries, the situation is different. Even
light or moderate earthquakes are acting in the areas of the old cities where the
number of non-engineered buildings (buildings erected ignoring any anti-seismic
rules) is dominant. Although is very important to mention that during 2003 Iran-
Bam earthquake, the great majority of damage was not produced in historical
buildings but in the new buildings, erected without any anti-seismic measures
(Zahrai and Heidarzadeh, 2004). In these cases the main disaster is not only
economical, as in the first case, but it derives from the human fatalities due to the
collapse of old and non-engineered buildings. For these countries the most