×
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

How irregular is too irregular?

How irregular is too irregular?

How irregular is too irregular?

(OP)
I have a building where the footprint of the second story is 6 feet narrower than the first story. This offset occurs only on one side of the building- i.e. only along one perimeter wall line. It's a large building so the 6 foot offset is relatively minor. The overall square footage of the smaller second story is more than 95% of the overall square footage of the first story.

Does this qualify the building as irregular per ASCE 7-05 table 12.3-1? I designed the building as "regular" but now I have a plan review comment telling me to justify that it's not irregular. Any help or advice would be greatly appreciated!

Thanks!

RE: How irregular is too irregular?

Does this offset affect the lateral system in any way?  Is there an out-of-plane offset of the lateral elements?

I can't think of any other irregularity the situation could qualify for.

If you have a comment to "justify" that it's not irregular, I would just go down the list from 1-5, and say that it doesn't fall into any one of these categories that ASCE 7 defines as an irregular building.  

Offsets in floors are pretty common, a 6' offset is nothing.   

RE: How irregular is too irregular?

(OP)
Yes, it does affect the lateral system as both perimeter walls above and below the offset are shear walls. I'm trying to justify the offset by saying that the 6' is small. Also the floor diaphragm between these walls is a pretty substantial concrete on metal deck diaphragm that I'm thinking can transfer any offset load.

I'm just not very good at "argueing" with plan reviewers...  

RE: How irregular is too irregular?

Since irregularity concerns mostly affect how the structure behaves under lateral load, I would check for any unintended or unusual load redistribution both locally and globally.
One concern that comes to mind right away..how does the offset affect the assumed stiffeness of that line of shear walls?
Since the shear walls are offset 6', the lateral shear has to be transferred from the top shear wall thru the 6' deck to the bottom shear wall.....shear flow can accomodate this as long as all the resulting loads are accounted for and the stiffeness of that 6' deck is equal or greater than the stiffeness of the shear walls.
The question for me would be the overturning loads from the top shear wall...they don't line up with the lower and if resisted by a beam and not a local col. could increase the flexibility of the top shear wall and thus reducing the stiffeness along that perimiter. Kinda long-winded, but if there is some doubt that it does not qualify as irregular, then one has to analyze it as is and try to account for all the loads in the given situation.

RE: How irregular is too irregular?

You do have a horizontal irregularity per T12.3-1 Type 4, however you do not have a vertical irregularity (T13.3-2).  Hence, you would be required to follow the restrictions listed in section 12.3.3

RE: How irregular is too irregular?

anybody else have difficulty reading the above posted article? It looks interesting, perhaps a version could be posted that is not garbled...

RE: How irregular is too irregular?

no problems here cvg, maybe you need to update your web browser.

RE: How irregular is too irregular?

got it, I had changed the zoom level in internet explorer and that apparently garbled the content of the web page...

RE: How irregular is too irregular?

(OP)
Thank you so much! Everyone has been very helpful! If you think of anything else that might apply or help me I will continue to appreciate your support.

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