Earthquake Engineering for Structural Design

Earthquake Engineering for Structural Design

Earthquakes were the cause of more than 1.5 million deaths worldwide during the
20th Century. During the beginning of the 21st Century the number of deaths was
about half a million. This is an unacceptable finding, because earthquakes can no
longer be regarded as natural disasters, since the main cause of this huge number of
casualties is the inadequate seismic resistance of the building stock, lifelines and
industry, which could be avoided. Earthquakes do not kill people, but the building
collapse can do it. It is an unbelievable situation that, after a century of research
works, each strong earthquake brings new surprises and creates the situation that
new lessons have to be learnt. After a series of devastating earthquakes during the
last years of the past century (1994 Northridge, 1995 Kobe, 1999 Kocaeli and
Taiwan earthquakes), it has been recognized by society that both seismic hazard
and risk have to be reassessed.
Important progress was made in the last period, but many problems remain
unsatisfactorily solved. Therefore, now is the right moment to analyze the level of
current knowledge and to identify the challenges for future research works and for
the next code generation. This is the main intention of this book. The progress in
understanding and controlling the complex phenomena of the earthquake
production can be analyzed both from scientific and practical points of view.
From the scientific point of view, the main effort must be directed towards the
inner understanding of the complex phenomenon of an earthquake. Some new
fundamental disciplines, developed in the last decades, must be deeply studied.

Earthquakes represent the largest potential source of casualties and damage for
inhabited areas due to natural hazard. Although the location varies, the pattern is
the same: an earthquake strikes without warning, leaving cities in rubble and
killing tens to hundreds of thousands of people. Worldwide during the 20th
Century, there were ten earthquakes killing more than 50,000 people and over 100
earthquakes killing more than 1000 people (FEMA 383, 2003). Every year,
something like five thousand to ten thousand people die during earthquakes
worldwide. The 1976 Tangshan-China (magnitude M 8.0), the worst earthquake in
recent times, killed over 600,000. Among these terrifying data, the moderate 1994
Northridge in Los Angeles (magnitude M 6.7), which killed 60 people, and 1995
Kobe in Japan (magnitude M 6.9), which killed 5600 people, seemed to be
relatively insignificant. Nevertheless, these two earthquakes have changed the
direction of earthquake engineering research throughout the World (Blakeborough,
2002). Two main reasons produced this crucial change.
The first reason lies not in the number of dead, but in their economic costs.
Each event was a direct hit by a moderate earthquake on a dense built-up area. In
Northridge, around 15,000 buildings had to be demolished, resulting in a total loss
ranging from $15bn to $40bn. In Kobe, 180,000 buildings were destroyed or
seriously damaged, the repair costs being estimated in the range of $90bn to
$150bn. Each earthquake set a record loss for natural disasters both for the USA
and Japan, respectively. Following these earthquakes, it was immediately apparent
that the old principles for seismic design had to change. Whereas the previous
principles had been primarily oriented to safeguard buildings against collapse, the
new and more refined rules are devoted to reduce the damage costs, by keeping the
non-structural elements and the structures in an acceptable damage level. So, the
principles of Performance Based Seismic Design were set up


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