×
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

Amplification for Accidental Torsion Per UBC97 and ASCE

Amplification for Accidental Torsion Per UBC97 and ASCE

Amplification for Accidental Torsion Per UBC97 and ASCE

(OP)
Hi all:

First, I tried to look for a thread discussing what I am about to pose but I wasn't able to find any so here it goes:

For discussion sake, suppose I have a building with applied earthquake and gravity loads and thus producing displacement on ends having a magnitude of -20mm and +20mm respectively from it's undeformed shape. Is it correct if I solve for the average displacement algebraically, which would render Ax as infinite? Or will the correct approach be a relative displacement (delta min = 0 and delta max = 20 + 20 = 40mm) in order to get a value?

I have a gut feel that the building has a torsional irregularity but I cannot seem to figure otherwise through computations. Is there something I am missing here?

Would appreciate if anyone would shed some light here.

Thanks!

RE: Amplification for Accidental Torsion Per UBC97 and ASCE

ACI codes give guidence on what constitutes "torsional irregularity" as where the drift at the diaphragm edge is more than 20% than the centre of the diaphragm.

Your hypothetical case of -20mm & +20mm is a bit much and probably could only occur if the diaphragm was subject to torsional force only and no horizontal shear.

I think your -20mm & +20mm probably comes more from a calculation or modelling error.

RE: Amplification for Accidental Torsion Per UBC97 and ASCE

The final deflection should be something like a net translation (at the mass centroid) plus a net rotation. The code equations essentially relate these two displacements relative to each other. So, look at the centroid displacement. If it is zero, and you've only got a net rotation, then you have probably done something wrong with your analysis and that code equation becomes meaningless.

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