TOPIC #2: THE 1994 NORTHRIDGE
EARTHQUAKE: SEISMIC BASE ISOLATION
The current investigation is to determine how well four buildings employing
the passive structural control called seismic
( base) isolation has survived
the 1994 Northridge earthquake. To score the buildings performances with
the help of field records, a procedure for comparison of real base
isolated structures with their hypothetical bench-marks had to be chosen.
To compare promise
a mathematical model had to be reduced to a SDOF system excited horizontally
in accordance with a recorded on a basement real time history. No sophistication
is warranted because the expectations were expressed in terms of the maximum
acceleration of a SDOF system. Besides, the recording instruments in the
buildings were mostly random, scanty and assumed that the superstructure
would be rocking like a rigid body.
: BASE ISOLATED
BUILDINGS PERFORMANCES : CONCLUSIONS
1. The results of this investigation cast serious doubts on
the ability of the current analytical approaches in base isolation
research and engineering to predict accurately actual performances
of the buildings targeted for earthquake protection.
| 2. Will
the Northridge earthquake experience with the buildings mounted on base
do us any good? - It depends on our attitude to the data presented
in the chart above.
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