Analysis and modelling of the seismic behaviour of high ... - Ingegneria

2. DUCTILITY AND SEISMIC RESPONSE OF STRUCTURES
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and displacement history. The duration of ground motion is very short. For
far-field regions, the records in acceleration, velocity and displacement
have the characteristic of a cyclic movement with a long duration;
• the velocities in near-field regions are very high. During the Northridge and
Kobe earthquakes, velocities with values of 150-200 cm/sec were recorded
at the soil level, while for far-field regions these velocities did not exceed
30-40 cm/sec. Therefore, in case of near-field regions the velocity is the
most important parameter in design concept, replacing accelerations,
which are a dominant parameter for far-field regions;
• the vertical components in near-field regions may be greater than the
horizontal components, due to the direct propagation of P waves, which
reach the structure without important modifications due to soil conditions,
their frequencies being far from the soil frequencies.
Figure 2.5. Near-field vs. far-field ground motion features
after Gioncu and Mazzolani (2002)