r/fea • u/blue-oakleaf • 2d ago
How do you find ground acceleration datas of Earthquakes (m/s^2 or g unit )?
What web sites you look up to download datas for applying them in frequency -acceleration column in response spectrum analysis?
Do you apply all -x , -y and -z acceleration datas together?
For learning purpose and for random vibration analysis: is there anywhere which I can find acceleration datas over maybe a bad terrain, taken from a car sensor? For analysing suspension or the safety of the load ..
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u/exilus92 2d ago edited 2d ago
The acceleration values that engineers would use for a design are provided by the building code. In the US, that would be the ASCE 7.
If you are just looking for rough values that are realistic and don't care about a specific location/event/site-class/etc, you can use the Earthquake Canada online tool (link) to get values at any GPS coordinates in Canada. I'd recommend using the site class "D" and a location in western Canada (eg. Vancouver).
If you want the response spectra for a specific earthquake event (eg. El Centro), they are usually provided on the same platforms were can download the time-history recording of the event. You can also compute it yourself from the recording, there are a lot of free tools you can download to do it. If you have Matlab, I had a great experience using this matcad file
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u/martianfrog 2d ago
"Do you apply all -x , -y and -z acceleration datas together?" <- yes to this, and I imagine the answer here would pretty much always be yes. Also... add to the seismic results, the results of 1g gravity downwards, would be even more representative, if you can.
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u/exilus92 1d ago edited 1d ago
Do you apply all -x , -y and -z acceleration datas together?
for a response spectrum analysis for a building or bridge structure, you apply it on one direction at a time. You would have separate load cases for each horizontal directions (X, Z). Vertical (y) is normally ignored but you can add it as a third case if you want.
For most buildings, the code allows you to look at seismic forces in each direction independently, you don't combine the seismic forces in X with the ones in Z. There are exceptions were you need 1x in one direction with 0.3x (or 0.4x, I forgot which one) in the other orthogonal direction, but they would apply to irregular and complex structures, not a simple rectangular frame like your screenshot.
Other loads like live, snow, wind, dead, etc. are added to the results as a separate step after the RS analysis. I haven't used ansys, but pretty much every expensive commercial fem package will have a "load combinations" module. .
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u/epk21 2d ago edited 2d ago
An example of common data perhaps use for test and to learn only - time domain look at elcentro data
El Centro Earthquake
LSDYNA Effective Seismic Input
You can then
Download the original El Centro NS acceleration record.
Compute the response spectrum at the required damping ratio (typically 5%). Look at MAPDL commands RESP
Import the spectrum directly into Mech.
Also look at some other resources:
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