Ground Motions and Structures - Earthquake Engineering for Structural Design - page 298

298 Earthquake Engineering for Structural Design

5
4
3
2
1

500 1000 1500

Distance (m)

(b)

Figure 8.3 City-site effect for Nice (France); (a) Various building density;
(b) Amplification factor (after Semblat et al, 2000, 2002a, b)

8.2FOUNDATIONRESPONSE

8.2.1BasicConsiderations

The evaluation of the seismic bearing capacity of foundations has not received much
attention from the earthquake engineering community. On one hand, it can be
recognized that the cyclic behavior of foundations has been extensively studied in the
last decade, with the development of impedance analyses, but at the same time very few
researches have initiated on their behavior at failure due to the seismic loads. The major
reason probably lies on the few observations of foundation failures during earthquakes
(Pecker, 1996). This situation changed after the 1985 Mexico City, 1999 Kocaeli and
1999 Chi-Chi earthquakes, when very bad behaviors of some foundations due to
settlement, tilting and overturning were observed. Significant improvement in the
seismic design of foundations has been reached in the last few years after these events.
Once the ground motion on the site has been evaluated, the structural designer needs
to proceed with the selection of the foundation system and its sizing. For this purpose,
he appeals to the Foundation Engineering, which is an amalgam of experience,
judgment, technical knowledge, theory and practice, being one of a most challenging
task for the structural engineering. In the last period, due to the requirements developed
in the frame of Earthquake Engineering, the problems are complicated by the necessity
to use the knowledge of the dynamic soil mechanics, soil-foundation-structure