×
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

base shear in dual system for a multistory bldg

base shear in dual system for a multistory bldg

base shear in dual system for a multistory bldg

(OP)
g'day!
i have a 3D model of a multistory bldg in etabs with a dual sytem, a shearwall and moment resisting frames.
how would you check your base shear on moment  resisting frames that these frames independently resist 25% of the base shear and 75% on the shear wall according to the UBC code?Can i directly use the horizontal reactions on their supports?

RE: base shear in dual system for a multistory bldg

Save the model as a separate file and delete the shearwalls.  Apply the 25% earthquake load to the moment frame system.  Check the resulting forces in the moment frames versus the forces from the original model.  Design for the worst case.

RE: base shear in dual system for a multistory bldg

Dear GENZO,

If you have a little time to check it by hand calculation for the shearwall using one of the familiar method, it will be more accurate..

See You,
ERKAN

RE: base shear in dual system for a multistory bldg

I don't agree with taro. If you check the frames "alone" probably they will deflect in a different way than linked to the walls.
On your original model you have to compare 25% of the base shear vrs the loads on the frames outcoming from a torsional distribution analysis. Usually  the 25% requisite governs.
MMena

RE: base shear in dual system for a multistory bldg

tacmena,

According to the SEAOC seismic design manual, "This 25-percent requirement may be interpreted in two ways
a. Q'E may be found by an equivalent lateral-force analysis of the independed moment-frame using 25 percent of the design base shear.
b. Q'E may be found by factoring the combined... system Q'E value such that Q'E corresponds to the action that would occur if the portion of the base shear resisted by the moment frame VF were to be at least equal to 25 percent of the design base shear V."

Either approach is valid.  The purpose of a dual system is to provide a secondary load path to increase the reliability of the system when the primary system degrades.  Either approach will work because the 25% force requirement is arbitrary and the force distribution will change from your initial elastic assumption anyway.  Your force distribution at ultimate levels will not be accurate unless you perform a nonlinear analysis anyway.

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