Learning from Earthquakes - Earthquake Engineering for Structural Design - page 96

- in the 1950s the dynamic concept was enhanced by the acceleration
spectra method;
- from 1950 to 1980 analysis methods were developed and knowledge
about non-linear behavior of structural components was enhanced;
- since 1980 to present, sophisticated computer programs have been, and
continue, to be developed, to facilitate the design of complex structural
systems and the study of their non-linear behavior.
On January 1995 a geological fault which had been quiet for hundreds of years
under the sea near Kobe, in central Japan, suddenly began to break. Houses in
Kobe and neighboring cities collapsed instantly, killing thousands of people and
producing the most known damaging earthquake in the world history. Considering
the evolution of the means of conveyance, from the horse cart in San Francisco to
the high speed trains in Kobe, the image of the collapse of the Hanshin
Expressway, shown in Figure 3.23, appears as dramatic as the one of the dead
horses in San Francisco.
Where is the progress in seismic design, if the consequences of an earthquake
remain the very same as hundred years ago?
The answer is related to the fact that during the period from San Francisco and
Northridge-Kobe earthquakes, the majority of events occurred far from very
urbanized areas. Therefore, the specialists cannot have the representation of the
consequences of an earthquake shaking a densely populated city. The existing code
provisions consider only earthquakes that occurred in normal conditions, because
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Figure 3.23 Dramatic picture of the Hanshin Expressway collapsed during the
1995 Kobe earthquake (courtesy of Fischinger et al, 1998)