Page 467 - Industrial Power Engineering and Applications Handbook

Testing of metal-enclosed switchgear assemblies 141441

1 80

150

1 1'20
7 0.90
2
C
2
$
- 060
a!
::
7
0.30
Period in seconds (T) -
0 00 c
0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 2.00 2.20 2.40 2.60

Figure 14.13 Typical broad band floor response spectra showing the floor acceleration at different damping levels

40 a mathematical model for analytical assessment or
Damping - 5% deciding the level of ground movement and frequency
I\ of excitation etc. To assist those in the field, the
35 ,' International Association of Earthquake Engineering
'\
EL Centro - Sd I (IAEE) has prepared a world list, coding the various
30 (USA) -w' countries on the following bases:
I
A Seismic zones
25 Seismic coefficient
--. Chamoli , JBiiF Acceleration of ground motion (.;)
.. (India) Velocity of ground motion (X), and
$20
C u Displacement of ground (x).
5 15
5 The above factors must be taken into consideration while
3
6 constructing an RS.
10
Floor response spectrum (FRS)
5 Some equipment will be on the ground, and some on
floors above the ground in which case floor movement
Period in seconds (T) ~ - movement is different from ground movement because
0 must be considered rather than ground movement. Floor
04 08 12 16 20 24 28 of structural behaviour, characteristics and filtration of
ground frequencies. Filtration of ground frequencies may
Figure 14.14 Displacement response spectra of the Koyna lead to resonance and quasi-resonance conditions and
(India), Chamoli (India) and EL Centro (USA) earthquakes magnify the floor movements. compared to ground
movements.
level. due to filtration, discussed later. It is, however, Required response spectrum (RRS)
observed that most of the vibrating bodies fall in a
frequency range of 2-15 Hz. This is the response spectrum, constructed for a
Any of the three RS is adequate to derive a time particular location, for a future earthquake. It is based
history of an earthquake to simulate test conditions in on seismic studies conducted for that region and
a laboratory. This, however, being a complex subject, past seismic records of and around that region, if
assistance must be obtained from experts in the field available. It forms the basic parameters for the design
for constructing an RS for laboratory testing, preparing and testing of an object.