New Challenges in Seismic Design - Earthquake Engineering for Structural Design - page 2

losses of $100bn to $200bn for a Californian earthquake and over $1000bn for a
Tokyo earthquake, if the 1923 earthquake were to happen today with the same
magnitude (Gioncu and Mazzolani, 2002). The growing world urban population
increases the number of cities located in seismic areas over some earthquake
sources. The Northridge and Kobe earthquakes generate a new research direction,
the effects of near-source earthquakes on the structures situated in epicentral areas.
Therefore, the structural response can be predicted fairly confidently, but
these achievements remain without real effects if the accurate determining of the
seismic actions is doubtful (Gioncu and Mazzolani, 2006). The elimination of the
gap between the advances in Engineering Seismology and Earthquake Engineering
is a major challenge of the new approaches in Seismic Design.
1.1.2WaystoDevelopTheseNewChallenges
One of the main goals in Seismic Design is improving the understanding of
earthquakes and their effects. This activity comprises the range of disciplines from
Seismology and Engineering Seismology to Earthquake Engineering. The
following aspects must be considered to achieve this target (FEMA 383, 2003):
Improve earthquake monitoring. Seismic hazard identification and risk
assessment are critical components of earthquake mitigation strategy. Under this
goal, a monitoring system, based on the regional networks of instrumented stations,
on the use of satellite-based observations (GPS monitoring stations) and associated
data centers, has been developed (FEMA 383, 2003). The most useful data for
seismic design are obtained from the seismic stations, by means of recorded
accelerations, velocities or displacements. The realization of an efficient network
of stations is a very difficult task. The station site and spacing requirements for
seismological researches are very different from those for earthquake engineering
purposes. Seismologists, interested in the study of the Earth structure, want their
stations to be located at quiet sites, as far away from any human activity as
possible. On the other hand, earthquake engineers want instruments in the built
environment of urban areas. Strong motion recordings useful for engineering
purposes must be within 20 to 50 km from the earthquake-rupture (depending on
site soil characteristics). A regional seismic network with stations spaced by
several hundreds of kilometers does not yield the information about the near-
source strong ground motions, required for earthquake engineering purposes.
Studies indicate that a station spacing of about 1 km or less is necessary in order to
reduce the observed variances in strong motions. One of the main problems of
strong earthquake monitoring refers to the uninhibited or lightly populates areas,
where the implantation of a dense station network is impossible. Therefore, the
problem of seismic monitoring is not technical, but a political and financial
problem (Lee, 2002).
Improve understanding of earthquake occurrence. In the last decades,
Seismology has made significant progresses in understanding the basic physics of
earthquakes. Together with these progresses, modern technologies such as Global
Positioning System (GPS) allow seismologists to forecast the overall long-term
seismic activity. Yet, earthquakes continue to be a major threat to our society, as