×
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

Wood shear wall uplift load combinations

Wood shear wall uplift load combinations

Wood shear wall uplift load combinations

(OP)
    When we design hold downs for wood shear walls, we use the load combination (0.6-0.14SDS)D+0.7pE (seismic) and 0.6D+W (wind) to calculate the uplift. In an other word, the formula we use are T=(Mot-(0.64-0.14SDS)Mr)/L (seismic) and T=(Mot-0.6Mr)/L. We got many projects approved using these equations. In other people's spreadsheets, we found that they use safty factors instead of those ASCE load combinations. For example, in Daniel Li's spreadsheet, he uses safty factors 0.9 for seismic and 2/3 for wind. In an other word, he uses T=(Mot-Mr)/(0.9L) (seismic) and T=(Mot-Mr)/(2/3)/L. In his method, the dead load helps more to reduce the uplift tension. Does any one have any idea which method is right, or if you think neither is good, what do you use?
     An other question is that in the book 2006 IBC STRUCTURAL/SEISMIC DESIGN MANUAL, the author uses the overstrength factor, omega, to evaluate the overturning moment. That results a gread tension value and is not practicable. We never use it and no plan checker questioned that so far. Any idea reguarding this issue? Any information will be appreciated.
      Thank you very much.

RE: Wood shear wall uplift load combinations

I use the ASCE combinations like you use, I use the overstrength factor to factor up the load for drag connections with seismic loading.

RE: Wood shear wall uplift load combinations

Don't you also have to apply the overstrength factor to discontinuous shearwall holddowns that create a soft story condition?

Mike McCann
MMC Engineering

RE: Wood shear wall uplift load combinations

(OP)
According to the ASCE, I think we need to apply the omega to discontinuous shearwall holddwons. Please tell me if I am wrong. I discuss this with some other PE's, most of them do not use overstrength factor to fator up the overturning momnent when designing shearwall holddwons. If the omega is applied to the holddwon design, the uplift seems too large to be pratical, especially for residential houses. We did not fator it up in some projects in different cities and no plan checkers asked for that overstrength factor in designing holddowns. I feel very confused. I'll appreciate if anyone can educate me with this question.
Thank you.

RE: Wood shear wall uplift load combinations

yes, this is a very good question and i have found several different viewpoints, none of which i consider to be the ultimate authority.  i have found a few referecnes that say you can avoid the overstrength by increasing embed depth so that the steel fails instead of concrete.   

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