CMU expansion joins

[kenwallet]

On one of my project, I called out CMU expansion join at one side of the door and garage door. The contractor requested to move the join 2 to 3 feet away from door/garage opening. I check on internet some CMU web site suggested and recommended to place CMU expansion join where wall thickness different such as pilaster and wall or by the door/garage opening. After I read the article it makes sense to place by the door/garage opening. I completely forgot that I have door/garage lintel reinforcing extend beyond both sides of the opening about 18 – 24”. I could not locate the expansion join in my CMU book (red cover). Does any one have any suggestion or correct reference to place the CMU expansion joins?

 

[271828]

Depends on the details of your situation. In general, I don't see a reason to not move it over, say 32" or 48" from the door.

One thing to think about is arching action. If you're counting on the CMU above your opening to arch, then you don't want the EJ too close to the door.

Do you have other cladding EJ to coordinate also? That might set your CMU EJ location.

Anyway--sorry for the lack of solid answer. Not sure there is one.

 

[kenwallet]

My building is rectangular shape 30’x 45’. I tried to locate my EJ at 25' max (If I remember correctly, 25’ is a good number). Now all my revised EJs are located 32" one side of the door. All of my EJ locations are not exactly the same as the information which I gather from internet web site. When I sent the revised EJ location to the contractor, I crossed my finger and hope this is the right choice that I made.

 

[civilperson]

24' is a better number for 8" thick CMU. (divisable by 16")

 

[concretemasonry]

Just a note on the terminology -

The correct term for the joints in concrete masonry is CONTROL JOINT and not EXPANSION JOINT. The concrete masonry industry (NCMA) uses the term in TEK notes since it better describes the function of the joint. ACI530 uses both contraction joint and control joint in one area of the commentary. ACI uses expansion joint for glass block and brick.

Expansion of a concrete masonry wall is very rare and occurs only under very specific conditions. The major changes in wall movement are generally shrinkage due to moisture, curing shrinkage and carbonation shrinkage. Temperature, which can cause expansion is a very minor item unless you build a wall at very low temperatires and subject it to very high temperatures. Even in this case, the shrinkage factors overcome the minor expansion factor.

Clay brick is different material and has a long term expansion from aging and alternate wetting and drying. The shrinkage factor of the mortar is still present, but does not always offset the expansion. This is one of the reasons for soft horizontal joints in brick veneer construction since the structure itself has an opposite long term reaction due to creep and shrinkage (concrete frame or masonry).

Dick