Conversion of Time History to Response Spectrum
Conversion of Time History to Response Spectrum
(OP)
Hi,
I want to convert a time history record of an earthquake into a response spectrum. I am aware of the theory behind this but would like to locate software that can do it for me without setting out to write something myself. Has anybody developed something that they would bewilling to share, or is there any Freeware out there that you can recommend?
With thanks.
I want to convert a time history record of an earthquake into a response spectrum. I am aware of the theory behind this but would like to locate software that can do it for me without setting out to write something myself. Has anybody developed something that they would bewilling to share, or is there any Freeware out there that you can recommend?
With thanks.





RE: Conversion of Time History to Response Spectrum
RE: Conversion of Time History to Response Spectrum
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Eng-tips forums: The best place on the web for engineering discussions.
RE: Conversion of Time History to Response Spectrum
It will cost you $40 for the subscription, but it has plenty of simple programs in matlab and C++.
RE: Conversion of Time History to Response Spectrum
clear all;
%
fs = 1000; % sampling freq.
T = 1/fs;
TM=3;
t = 0:T:TM;
x = cos(50*t)+2*sin(80*t+pi/3)+3.5*cos(155*t+pi/6)+4*cos(180*t+pi/4); % example signal
%
data=x;
N=length(data);
Fmax=fs;
delta_f=(1/(TM*Fmax))*Fmax;
f = 0:delta_f:Fmax;
F=fft(data);
figure
plot(f(1:N/10),abs(F(1:N/10))),grid
title('FFT'); xlabel('Frequency (Hz)');ylabel('Amplitude')
Fe
RE: Conversion of Time History to Response Spectrum
Fe
RE: Conversion of Time History to Response Spectrum
- Steve
RE: Conversion of Time History to Response Spectrum
Fe
RE: Conversion of Time History to Response Spectrum
Fe
RE: Conversion of Time History to Response Spectrum
Just returned from vacation hence the late response. Thanks to all who responded, you have all been most helpful. I dont have Matlab but "btrueblood" can you tell me more about the Excel fourier transform capability?
With thanks
RE: Conversion of Time History to Response Spectrum
Fe
RE: Conversion of Time History to Response Spectrum
Tools / Add-ins / check the box "Analysis Tookpack"
Then you can choose Tools/Data Analysis / Fourier Analysis
If you want to use VBA, you can also install the "Analysis Tookpack - VBA" tookpack which will give you access to the VBA "fourier" function. Note that complex numbers are represented as stringes.
The limit for excel's FFT is 4096 points.
=====================================
Eng-tips forums: The best place on the web for engineering discussions.
RE: Conversion of Time History to Response Spectrum
=====================================
Eng-tips forums: The best place on the web for engineering discussions.
RE: Conversion of Time History to Response Spectrum
- Steve
RE: Conversion of Time History to Response Spectrum
Actually, the Excel function is fairly straightforward, if you are at all familiar with FT analysis. It's limited in many ways, but I've used it before to get reasonably quick, cheap, usable data output. Excel is less a hammer than a bloated, expensive, cumbersome swiss-army-knife and food processor all rolled into one. That said, it's usually already installed on most machines, and most users are familiar with it.
RE: Conversion of Time History to Response Spectrum
....and hell we even wrote the external m-code.. all you have to do is cut and paste.
Fe
RE: Conversion of Time History to Response Spectrum
Fe
RE: Conversion of Time History to Response Spectrum
I have posted a shock response spectrum tutorial at:
ht
The tutorial is geared toward aerospace shock, but the principles and formulas are the same for earthquake shock.
The required input is a base acceleration time history.
Tom Irvine
http://www.vibrationdata.com
RE: Conversion of Time History to Response Spectrum
http://en.wikipedia.org/wiki/Shock_response
So it looks like you have to take the base acceleration TWF, input it into SDOF with frequency f1, damping d0, determine peak acceleration of the response r1, plot point (f1,r1)
Then repeat with frequency f2, damping d0, compute response r2, plot point (f2,r2).
=====================================
Eng-tips forums: The best place on the web for engineering discussions.
RE: Conversion of Time History to Response Spectrum
=====================================
Eng-tips forums: The best place on the web for engineering discussions.
RE: Conversion of Time History to Response Spectrum
Fe
RE: Conversion of Time History to Response Spectrum
Fe
RE: Conversion of Time History to Response Spectrum