Page 117 - Çevre Şehir İklim İngilizce - Sayı 4

Cenk Alhan - Mert Hacıemiroğlu

extending dominant period and increasing damping, and decreasing relative
storey drifts due to changing rigid-body-like first mode behavior. Thanks to
the seismic isolation, which allows the uninterrupted use of the structure
after an earthquake, even during an earthquake, there is no need for highly
ductile detailing of the superstructure. It also allows existing structures to
be reinforced against earthquakes. However, in order for a structure to be
designed with seismic isolation, the soil conditions must be suitable, that is, it
must not be located on soft ground that increases long-term ground motions,
it must be heavy enough, not be too vulnerable and its surroundings must
allow it to move freely (Mayes and Naeim, 2001).
The most common types of seismic isolators include rubber bearing
(elastomeric) and curved surface friction pendulum types. Rubber bearing
isolators consisting of rubber and thin steel plate layers are available in three
main types: Natural Rubber Bearing
provides a damping at the level of 2%-4%, while Lead Rubber Bearing
Isolators allows a damping up to 30% due to the lead core which is located at
the center and with a diameter ranging from about 1/3 to 1/6 of the isolator
diameter. The amount of damping provided varies depending on the diameter
and dynamic yield strength of the lead, as well as the horizontal displacement
level. Finally, High Damping Rubber Bearing does not have a lead core; it
can provide a damping of about 12% due to addition of substances such as
resin, etc. (Whittaker et al. 2018). Curved Surface Friction Pendulum Isolator
(Friction Pendulum) was developed by (Figure 1) Zayas et al. (1990), which
is made of materials resistant to environmental impacts, provides seismic
isolation by using geometric properties, gravitational acceleration and
pendulum movement; and the success of these insulators has been proved by
the experiments. In order to bring the large insulator displacement demands,
occurring in areas very close to the fault line, to reasonable limits, sometimes
there is a need to use additional damps in the isolator system. In such cases,
the damping rate can rise far above 30%.

106 The Journal of Environment, Urban and Climate