Challenges for the Next Generation of Seismic Codes - Earthquake Engineering for Structural Design - page 468

the ground motion modeling. The structural capacity is the ability of the structure
to resist these effects without failure. Looking to the developments of Engineering
Seismology and Earthquake Engineering, it is clear that the major efforts of
researchers have been directed towards the structural response analysis. Therefore,
the structural response can be predicted fairly confidently, but these achievements
remain without real effect if the evaluation of the seismic actions is not accurate
and, therefore, doubtful. In fact, the prediction of ground motion is still far from a
satisfactory level, due to both the complexity of the seismic phenomena and the
communication lacks between seismologists and engineers. This remark can be
confirmed after each important earthquake, when new and new in situ lessons
regarding the characteristics of ground motions are learnt, instead of providing the
missing data from seismological studies in advance. So, the reduction of
uncertainties in ground motion modeling is now the main challenge in structural
seismic design. This target is possible only if the impressive progress in the
Seismology will be transferred into structural design. Three important
developments during the second half of the last century contributed to the rapid
advances in Seismology. First, the development of Plate Tectonic Theory, which
offers now a clear and conceivable framework for the generation of the majority of
earthquakes. Second, the establishment of fault mechanism producing different
earthquake types, having very different ground motion characteristics. Third, the
computer technology, which opened new possibilities to analyze a large amount of
data and to model the fault rupture process, in order to simulate the ground
motions. Any progress in Earthquake Engineering is impossible without
considering the new amount of knowledge, recently cumulated in Seismology.
Today, after these improvements in knowledge, it can be assumed that there are
three different earthquake types, which should be considered in the structural
design: interplate, intraplate and intraslab earthquakes. There are such big
differences between the ground motions generated by these earthquakes that the
ignorance of these aspects can be considered as a shortcoming of code provisions.
In this context, the engineering seismologists are now paying more concern to
establish the differences in the main characteristics among these earthquakes. At
the same time, the task of earthquake engineers is to take more care about the
structural response of these earthquake types.

10.3.3 Critics of Current Design Methodologies

Since its introduction to Earthquake Engineering by Housner in the 1950s, the
response spectrum has become an essential tool in structural analysis and design.
But today, after the impressive development of the Earthquake Engineering
Science, some shortcomings in current practice have been identified (Gioncu and
Mazzolani, 2006):
-

The codes historically were developed based on the experience of few
recorded ground motions not sufficiently close to the causative faults, due to
the absence of a dense network of recording stations. In the last period this
situation is changed in some very urbanized seismic zones and the recent
earthquakes, such as Northridge (USA), Kobe (Japan), Chi-Chi (Taiwan) and