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Seismic response
[Subject Prev][Subject Next][Thread Prev][Thread Next] To: "Sseaint Org" <seaint(nospamat)seaint.org>
 Subject: Seismic response
 From: "gregory szuladzinski" <ggg(nospamat)bigpond.net.au>
 Date: Thu, 19 May 2011 19:01:56 +1000
Reply:
Alex,
Imagine a row of simple oscillators, with increasing natural
frequency.
This is your xaxis.
An earthquake comes and it shakes that row for a
while.
The motion of each oscillator is recorded. A peak response for each
of those oscillators
is noted and marked on the graph, above the oscillator, giving you
the yvalue.
The entire graph is a response spectrum.
It can be for displacements, velocities or accelerations. (All
oscillators have the same damping.)
Then comes your structure.
Each DOF is interpreted as an oscillator.
That mode will have the same peak accel as the corresponding
oscillator had.
To get a response at a node, you combine all considered
modal responses
according to some rules, for example SRSS. Same for bending
moments, etc.
If you want a simple, basic presentation of the entire
process,
you may look up my book "Dynamics of structures and machinery.
Problems and solutions."
(Wiley 1982). It is out of print now, but you can still run into
it.
It doesn't tell you what codes of practice require, but gives good
physical understanding.
Gregory from Oz.
Question from Alex Bausk:
If there is a task to calculate the response spectrum at a given node of
th=
e structure (over frequency domain) from a given ground motion record (acce= lerogram)=2C do I get it right that the only way to do this is to perform a= fullblown timehistory analysis? The logic behind this is=2C to calculate the spectrum you have to have the = actual response record at the desired node=2C and the spectral approach won= 't produce this kind of information. Is this right? Any reference to a textbook would be a very nice thing to have. Many thanks= in advance and sorry that I have flooded the list with my threads. Alex.

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