Earthquakes and Ground Motions - Earthquake Engineering for Structural Design - page 217

Chapter 7
Earthquakes and Ground Motions
7.1 GROUND MOTIONS EVALUATION AND EARTHQUAKE
ENGINEERING
7.1.1 Transfer of Engineering Seismology Knowledge to Earthquake
Engineering
The advances in Seismology and the special branch of Engineering Seismology
were presented in Chapters 4, 5 and 6. The proper definition of ground motions, in
order to evaluate the structural response, is the first field where the contact between
Engineering Seismology and Earthquake Engineering is directly established.
Earthquakes do not directly produce building collapse. Ground motions are the
real cause of seismic damage. The dynamic response of buildings to ground
motions is the most important cause of earthquake-induced damage in buildings.
Therefore, it is very important to understand in which way the sudden movements
of the source are transformed in ground motions at the building site.
The basic concepts of today's Earthquake Engineering were born almost 70
years ago, when the knowledge about seismic actions and structural response were
rather poor. Today, the earthquake-resistant design has grown within the multi-
disciplinary fields of Engineering Seismology and Earthquake Engineering,
wherein many exciting developments are predicted in the near future. Looking to
the development of the Engineering Seismology and Earthquake Engineering, it is
very clear that the major efforts of researchers were directed towards the structural
response analysis. As a consequence, the structural response can be predicted fairly
confidently, but these achievements remain without real effects if the evaluation of
seismic actions is doubtful. In fact, the prediction of ground motions is still far
from a satisfactory level, due to both the complexity of the seismic phenomena and
the lack of communication between seismologists and engineers. This remark can
be confirmed after each important earthquake, when new and in situ lessons
regarding the ground motions are learned, instead of providing in advance the
missing data from seismological studies. So, the reduction of uncertainties in
seismic action modeling is now the main challenge in structural seismic design.
This target is possible only if the impressive progress in Seismology will be
transferred into Earthquake Engineering. Any progress in this field is impossible
without considering this new amount of knowledge recently cumulated in
Seismology (Gioncu and Mazzolani, 2003, 2006).
Observations of damage after the earthquakes have shown that the earthquake
characteristics, very different from one site to another, can have a strong influence
on the structure performance. These characteristics reflect not only the source
properties, but also local effects and the site earth's configuration. In order to be
considered in seismic design of structures, it is very important to underline the