Page 136 - Çevre Şehir İklim İngilizce - Sayı 4

Seismic Isolation in Earthquake -
Resistant Structural Design for Resilient Cities

4.2 Behavior Under the Impact of Near-fault and Vertical Earthquakes
One of the two problems for seismic isolation buildings to cope with is the
long-period and high-amplitude “velocity pulses” observed in earthquake
ground motion velocity records in areas close to the fault, while the other
is that the amplitudes of the vertical acceleration component of earthquake
ground motion, especially in areas close to this fault, are very high (Elnashai
and Papazoglou, 1997; Papazoglou and Elnashai, 1997; Bray and Marek, 2004;
Memarpour et al., 2016). When the long periods of velocity pulses observed
in near-fault earthquakes are close to the isolation periods of buildings with
seismic isolation, a resonance-like behavior is observed and the isolator
displacement demands increase a lot (Hall, 1998; Alhan and Öncü-Davas,
2016). If this is not foreseen in the design, the insulators may exceed their
capacity, causing them to rupture or buckle. Similarly, vertical earthquake
accelerations are usually smaller than horizontal accelerations and the value
of gravitational acceleration. Usually, the pulls/lifts on the insulators are
observed on the edge/corner isolators depending on the overturn movement
under the horizontal earthquake motions while, pull/lift can be observed in a
large number of insulators due to high vertical ground accelerations in near-
fault earthquakes.
In order to numerically present the problem outlined above, a near-fault
earthquake record with a long period and high amplitude velocity pulse and
high vertical accelerations was specially selected and applied to the seismic
insulated building model created in Section 4.1. The characteristic features
of the El Centro Array #6 Station Record (RSN181) of the selected October
15, 1979 Imperial Valley-06 Earthquake are given in Table 3 (PEER, 2023). In
order not to change the characteristic features of the earthquake record,
no scaling has been performed. However, in order to compare the spectral
characteristics of the RSN181 recording with the horizontal earthquake design
spectrum used in the design of the seismic isolation system in Section 4.1,
in accordance with the TBDY (2018) – Chapter 2.5.2, the resultant horizontal
spectrum was obtained by taking the square root of the sum of the squares
of the spectra of the two horizontal components of the RSN181 earthquake
recording set and compared with 1.3 times the horizontal earthquake design
spectrum (Figure 10). As can be seen, the seismic isolation period calculated
by the lower limit properties, that is, around 4 s, the spectral acceleration
value of the RSN181 register remains slightly above the horizontal design
spectrum of 1.3DD1.

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