New Challenges in Seismic Design - Earthquake Engineering for Structural Design - page 3

we have witnessed during the seismic events of the last century and the beginning
of the new one. A major difficulty is due to the fact that an earthquake involves a
large number of elementary processes, so that, even if we understand the physics
governing each elementary process, the complex interaction between them makes
accurate forecasts of earthquakes very difficult (Kanamori, 2001). The Plate
Tectonics and Continental Drift Theories are a starting point for understanding the
forces within the Earth causing earthquakes. Three major types of plate boundaries
are recognized: divergent, convergent or transformed, depending on whether the
plates move away, toward, or laterally passing one to another, respectively. Ninety
percent of the world's earthquakes occur along plate boundaries. The earthquake
types depend on the boundary types. For instance, subduction occurs where one
plate converges toward another plate, moves beneath it, and plunges as much as
several hundred kilometers into the Earth's interior. In function of depth, two
different types of earthquake occur: interplate crustal and intraslab deep
earthquake, with very different physical characteristics. The remaining 10 percent
occurs in areas away from present plate boundaries, being the results of ancient
plate boundary configurations. The seismic movements of these earthquakes are
very different from the ones produced at present boundaries. All these aspects must
be considered for the understanding of earthquake occurrence.
Improve fundamental knowledge of earthquake effects. Among the most
important contributions to reducing earthquake losses, there are both the improving
of understanding and the modelling earthquake effects, including the source
properties, the wave propagation from the source to site and the local conditions
characterizing the site. This task implies the development of methods to generate
synthetic seismograms for the expected future earthquakes, incorporating improved
understanding of the rupture process and information about the fault type and the
properties of the surrounding earth's crust. At the same time, the identification of
the parameters of ground motions causing soil liquefaction, land sliding and
damage of structures (such as peak acceleration, ground velocity and displacement,
shaking duration, spectral content, etc.). The effects of near-source are of primary
importance for urbanized areas. These seismograms must accurately simulate these
parameters used by structural engineers in the seismic design process.
Improve the seismic design of structures. A new facet of Earthquake
Engineering research concerning the seismic structural response is based on the
reliance of integrated experimentation, theory, databases and model-based
computer simulations. Under this objective the priorities refer to improving the
understanding of behaviour and collapse mechanisms of various classes of
structures under different earthquake types, in order to establish new
methodologies for performance-based earthquake engineering. These new
methodologies must consider different design philosophies for structures situated
in low to moderate and strong seismic areas. The objective implies also developing
new materials, new technologies and new structural systems for earthquake
resistant structures.
Start development of next generation performance-based codes. The goal of
these activities assures the ability to reduce seismic vulnerability of structural
systems, learning from the lessons given by the last strong earthquakes and from