Learning from Earthquakes - Earthquake Engineering for Structural Design - page 71

Chapter3
Learning fromEarthquakes
3.1MAINLESSONSAFTERTHE STRONG EARTHQUAKES
3.1.1 The Paradoxof Design: Success through Failure
In spite of the great efforts made in recent years in solving satisfactorily the
problem of building design in seismic areas, recent earthquakes are capable of
producing more damage today than ever before. Besides, a marked increase of
financial losses can be observed (Fig. 3.1), especially during the catastrophic
decade 1985-1995, marked by the Mexico City, Loma Prieta, Northridge and Kobe
earthquakes. The main reason of this remarkable increase of damage costs in
recent years is due to the concentration of population and industrialization in high
seismicity regions. The rapid and in many cases uncontrolled urbanization of
metropolitan regions contributed to the vulnerability of their communities and
infrastructure. More recent earthquakes have occurred in these regions and the
events of Izmit and Taiwan produced great disasters due to the proximity of highly
urbanized areas. These events clearly shown that the design methodologies and
code provisions are not infallible . This is true especially in cases where the
earthquake sources are near to a densely populated area.
The paradox of structural engineers is that while engineers can learn what not to
do from failures, they do not learn how to do from successes (Petroski, 1985,
2006). The failure of a structure contributes more to the evolution of design
concepts than a structure successfully standing without accidents, on the condition
that the engineers have the capability to understand what happened (Gioncu and
Mazzolani, 2002).
Structural failures occur in part because the design process is subject to flaws
and failings of human nature. Failures persist, because the design process is
fundamentally carried out by a human mind in a human context. The structural
failures cannot be eliminated by the development of refined computational models.
A given situation where no structural failures occur, could be produced by an over
conservative design, wasting resources which might be better applied elsewhere in
the society (Petroski, 2006). Therefore, the failure of structures may be regarded as
a factor of progress in design, not a calamity, under the condition to learn the
lesson of each catastrophic event.
So, the main purpose of modern seismic design is only to reduce economic
losses, and at the same time to save human life, not to completely eliminate them.
The learning from disasters is the key to solve this problem. It is very interesting to
notice the hurry in which the structural engineers across the world rushed to the
sites of some produced quakes to study the damage. Their objectives: to gain a
better understanding of the geological faults, to determine why buildings and
structures failed, and to share these findings with other earthquake-prone zones
(Hays et al, 1999).