×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Contact US

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!

*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

Seismic Analysis Requirements in Areas with Low Seismic Activity

Seismic Analysis Requirements in Areas with Low Seismic Activity

Seismic Analysis Requirements in Areas with Low Seismic Activity

(OP)
Does anyone have any experience with interpreting the requirements of API RP 2A with regards to performing a seismic analysis when the SLE ground acceleration is less than 0.05g? For the specific project I am working (offshore jacket/topsides structure near Equatorial Guinea), the site-specific seismic analysis estimates an SLE ground accleration of 0.03g and and a DLE ground accleration of 0.171g. API RP 2A Sect 2.3.6.b.2 states that “For areas where the strength level design ground acceleration is less than 0.05g, e.g., the Gulf of Mexico, no earthquake analysis is required, since the design for environmental loading other than earthquake will provide sufficient resistance against potential effects from the seismically active zones.” This would seem to indicate that no seismic analysis is required. However, the fact that the DLE/SLE ratio is so large (5.7) concerns me and I think that perhaps a ductility level analysis should be performed to ensure the platform will not collapse under the rare, intense earthquake. Also, the Equatorial Guinea area has low environmental loading requirements, so it can't be assumed that the design for the environmental loading will automatically mean that the seismic criteria has been fulfilled as well. FYI, if the platform was designed per ISO 19901-2, then a seismic analysis would need to be performed since ISO 19901-2 has a lower threshold for performing seismic. My main goal is to find someone who has run into this issue in the past to see what the resolution was.

Thanks,
Jason Hrncir

RE: Seismic Analysis Requirements in Areas with Low Seismic Activity

Hi jthrncir :
I think it is better to perform DLE analysis. This is because of 2 things:
1. in API RP 2A Sect 2.3.6.b.2 states that "platform design would normally controlled by storm or other environmental loading rather than earthquake", this means it may be not adequate for special rare case like your case. the phrase "would normally" does not mean that it must be in all cases.

2. Sect 2.3.6.b.2 gave an example of Gulf of Mexico, which is a special case, and in this gulf the design would be controlled by storm or other environmental loading rather than earthquake if the strength level design ground acceleration is less than 0.05g.

I hope it helps
Mohamed

RE: Seismic Analysis Requirements in Areas with Low Seismic Activity

At that range, it could be possible to justify the structure using the DLE level accelerations, and remain in the elastic zone. This is a simpler check that a plastic analysis and if this passes, a plastic analysis wouldn't be required, I imagine.

This is covered in the next part in Section 2.3.6.b, API RP 2A.

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! Already a Member? Login



News


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close