×
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

Concrete Coupling Beams
3

Concrete Coupling Beams

Concrete Coupling Beams

(OP)
This is a new animal for me and I am trying to understand the intended design phylosophy of the ACI regarding these elements.  Did a search and really couldn't find much on the topic here.  

I have a situation where the local jurisdiction is requiring the use of these between concrete shear walls. I have a real problem with this in that the structure was designed using R=5 under Table 12.2-1 for a Ordinary Plain Concrete Shearwall System.  Section 21.7.7 of ACI refers to using these connectors between the shear elements of Special concrete Moment Frames (R=8) and Special Reinforced Concrete Shear Walls (R=6), which this is neither.

My question is whether their interpretation of the code is correct.  Is it the intention of the code to require these elements even in Ordinary Concrete Shear Wall Systems?

I noticed, too, that these elements are only effective if the slope on the steel is great enough - i.e. for use with short, deep beams between the concrete shear elements.  In that the comments were concerning the shear walls around elevator and stairwell walls that had little if any rigidity with respect to the rest of the system due to the openings, I don't see the code logicically applied.  I feel that these walls with the openings are really too short to be effective shear walls so no coupling beam should be required anyway.  Plus, having to add the coupling beam means having to widen the walls from 8" to 10".

Any comments?  

Mike McCann
MMC Engineering

RE: Concrete Coupling Beams

Mike,

I am not familiar with the code provisions you quote, but coupling beams are used extensively in high rise buildings.  The typical application is when the elevator walls are used as a core, and are the primary lateral load resisting element.  When you have elevators on each side of a lobby, the walls behind each bank of elevators form a C shaped element which is strong in one direction, but not in the other.  In the other direction, coupling beams force the two sides to act as a T-C couple.  The coupling beams act like the webs in a cantilevered Vierendeel truss.

The couplers are typically heavily reinforced, and the junction with the end walls requires special detailing.  These beams, and thus the walls, are typically 10" to 20" wide, depending on the building height, but sometimes much thicker.

If the walls you are referring to are not the load resisting elements, I think the requirement of coupling beams is illogical.

RE: Concrete Coupling Beams

If you are using an Ordinary Reinforced Concrete Shearwall System, seismic detailing of coupling beam is not required. You may still provide additional reinforcement around the openings (top, bot and sides). It is a good practice to add some diagonal bars but is not mandatory.

What version of ACI-318 & which is the governing building code? I believe you are not using Ordinary Plain Concrete Shearwall System with an R=5, which is incorrect.

RE: Concrete Coupling Beams

(OP)
Hokie:

That's exactly what I thought.  Thanks.

prsconsultant:

I am looking at ASCE7, Table 12.2-1, Seusmic Force Resisting Syetem B6, Ordinary Reinforced Concrete Shear Walls, R=5.  The codes in use are IBC 2006, and ACI 05.

Mike McCann
MMC Engineering

RE: Concrete Coupling Beams

Just finished designing a building with Ordinary Reinforced Concrete Shear Walls, R=5 with IBC 2006, and ACI 05. Definitely you don't have to detail the link beams for seismic.

RE: Concrete Coupling Beams

Check out AISC Civil engineering magazine May 2006 for an article on coupling beams in lift cores.

RE: Concrete Coupling Beams

Sorry that was ASCE not AISC

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