×
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

Seismic Reductions and Increases

Seismic Reductions and Increases

Seismic Reductions and Increases

(OP)
ASCE 7-10 12.13.4 allows a reduction of seismic loads (demand) at soil interactions (i.e. foundation) by 25%. Our california building code allows an increase in soil capacity by 1/3 for seismic loads. And lastly, we are allowed a 1.1 safety factor instead of 1.5 in retaining walls when we use seismic loads. Are all of these factors applicable simultaneously?

My understanding was that the 25% reduction in demand (3/4 of demand) was the same as the inverse (4/3 Capacity), hence, the 1/3 increase in capacity. But I was told that they are two different things and I can use both at the same time.

RE: Seismic Reductions and Increases

The way I interpret ASCE 7-10 §12.13.4, the 25% reduction in force is for overturning (foundation uplift) not bearing pressure. I would consult with the project's geotech concerning the 1/3 increase in soil capacity. Frequently, the bearing pressure is governed by settlement and the 1/3 increase assumes the foundation won't have significant settlement from the short term seismic loads.

RE: Seismic Reductions and Increases

(OP)
@wannabeSE: So you wouldn't decrease your overturning force (checking down push) and increase your soil capacity by 1/3 at the same time? The 25% reduction when checking uplift makes more sense to me. I'm a bit skeptical on double dipping when checking down push/bearing. Thanks.

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