×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Earthquakes, is it a shock or random vibration event?

Earthquakes, is it a shock or random vibration event?

Earthquakes, is it a shock or random vibration event?

(OP)
Earthquakes, is it a shock or random vibration event?

Im looking at a spec and it describes the earthquake in a SRS (Gs vs Hz) profile, but I thought it would be described in a random vibe (G^2/Hz vs Hz) because earthquakes can last longer than typical shocks (pulse, velocity,…).  

Any help would be greatly appreciated.

Tobalcane
"If you avoid failure, you also avoid success."

RE: Earthquakes, is it a shock or random vibration event?

Earthquakes are neither of those strictly speaking, as they fall under their own "seismic" type event. The g vs Hz is a response spectrum converted from a time history using single DOF springs on masses. This gives a characteristic shape of spectrum, which shock or impact spectra differ from greatly. The seismic response spectrum will have in general the greatest (most damaging) energy associated with the 5-12 Hz range, whilst the shock/impact damaging frequency will generally be a lot higher (in 100+ Hz range). Industry standard in the nuclear industry for the analysis of systems/structures is to use response spectrum for seismic and time history for shock/impact.


------------
See FAQ569-1083 for details on how to make best use of Eng-Tips.com

RE: Earthquakes, is it a shock or random vibration event?

(OP)
Thank you Drej for your response (no pun intended).  

Tobalcane
"If you avoid failure, you also avoid success."

RE: Earthquakes, is it a shock or random vibration event?

(OP)
Another question Drej, how would you run that on a shaker table?  I mean would you use a G^2/Hz vs Hz profile to simulate the earthquake?

Thanks!

Tobalcane
"If you avoid failure, you also avoid success."

RE: Earthquakes, is it a shock or random vibration event?

No, G^2/Hz vs Hz is a Power Spectral Density input (PSD), which is generally a random vibration signal. You need to obtain either the time history (e.g. acceleration/velocity/displacement vs. time) for the event or the response spectrum (e.g. force/acceleration/velocity/displacement vs. Hz) to represent the seismic input. Whether you use one or the other depends on the results you need as well as computer resources.


------------
See FAQ569-1083 for details on how to make best use of Eng-Tips.com

RE: Earthquakes, is it a shock or random vibration event?

(OP)
Thanks Drej!

Tobalcane
"If you avoid failure, you also avoid success."

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources