cmu bond beams

[bjb]

should horizontal rebar run continuous through control joints in cmu walls? I think it should because it can be used as diaphragm chord reinforcement (unless other measures are taken). I think the percentage of horizontal steel in the wall is typically low enough so that the continuous rebar doesn't lock the joint.

I ask the question because I recently saw this detail on another structural engineers set of plans.

 

[structural01]

Yes. I agree. The reinforcing should run throuth the joint to create continuity in the chord force. However, the reinforcing by itself may not be enough for the chord force. Additional, members maybe required.

Another option is to analyze your building as a "C" shape at the joint. You have to analyze your building for torsion. Also, lateral deflection must be checked.

 

[FSS]

Structural reinforcement, such as in bond beams associated with roof and floor diaphragms, should be continuous through the control joints. Nonstructural horizontal joint reinforcement would not be continuous. You can refer to NCMA's TEK #10-2A "Control Joints for Concrete Masonry Walls."

 

[bjb]

Thanks for your replies, that's what I thought.

 

[Lutfi]

I have a detail that I use all the time that allows rebar continuity through joints. I Use it for bond beams and tie beams a like. If you want a copy, let me know.

Since I live in Florida and I design most of CMU walls as shear walls, bond and tie beams become diaphragm chords.

Good luck

 

[bjb]

I was just reading my post and realized that part of what I said is wrong. What I should have said was that I had recently seen a detail on another engineers set of drawings that showed rebar in the bond beam stopping at the control joint. They also showed a smooth greased bar going across the joint, but in my opinion this prevents the bond beam reinforcing from functioning as a diaphragm chord. Sorry about the wrong wording of my sentence. On my drawings I indicate the bond beam reinforcing as being continuous. I also tell them what the length of lap splices in CMU are, and check it on the masonry rebar shop drawings.

Lufti, thanks much for the offer. My email is b.bidonde@ctmale.com. We run AutoCAD 2002 here, or you can also send it as a tiff or adobe image, whatever works best for you.

 

[MotorCity]

bjb,

I think you have control joints confused with expansion joints. You mentioned greased bars - these are only used at expansion joints to allow the expanding members to move without restraint. Reinforcing should be continuous across control joints. These joints are for aesthetic purposes as they help control the cracking pattern in the finished surface. Good luck.

 

[bjb]

Motor,
I don't have the two confused. The drawings that I saw by another structural engineer had the greased bars in the control joints in a CMU wall - it's not my design. You typically wouldn't have expansion joints in a CMU wall because it shrinks. Nonstructural reinforcement should not run continuous through a control joint according to NCMA TEK NOTE 10-2B, but structural reinforcement such as rebar for diaphragm chords should. The drawings in question by the other engineer appeared to have ALL horizontal reinforcing bars stopping at the control joints.