Masonry control joints in small buildings

[saaveze]

Hi Everyone,

What are your thoughts on vertical control joints for small reinforced masonry structures? For example a 12' wide x 20' long x 8'8" tall reinforced masonry building with one 4' wide door opening on one 12' wall and the same opening on one 20' wall. The 8" CMU walls support a reinforced concrete slab.

I have read most if not all posts related to CJ's in masonry walls and have not seen this topic covered for small buildings. The building is in an area with large changes in moisture and temperature.

Thanks!

 

[JedClampett]

I'd provide them at each of the 20'-0" walls somewhere where it's convenient (away from the opening at least 16 inches). We like to provide them every 24 feet (not always strictly followed) and I interpret that as a cumulative distance.

 

[oldestguy]

The openings are obvious places for cracks to occur. So, that's where they are of most use.

 

[hokie66]

Most reinforced masonry buildings of that size don't require control joints. It would depend a lot on the founding soil.

 

[saaveze]

Thank you for the responses. The foundation bears on sand classified as SP per USCS with an allowable bearing pressure of 1800 PSF. The building is for a water well pump house. Our client has many of these buildings around town and all were constructed prior to 2002 and some date back to the early 1960's. Its interesting looking at the differences between all the buildings as some have control joints in the 20 walls while others do not have any. Its hard to tell if any cracks have been repaired since all the buildings have relatively fresh paint.

Jed - The building has reinforced bond beams at 48" O.C. Would you cut the reinforcement at the CJ or allow it to continue and score the block?

Thanks

 

[JedClampett]

To form the CJ, make a vertical grout joint. Place a PVC control joint material in the joint. Continue the bond beam steel. No need to score the block. Use the vertical grout and the PVC as your weakened plane.

 

[SteelPE]

I'm not sure I would provide a CJ along the 20' width. I would more than likely request them at the corners though (not sure if you were asking for that or not). When asked I try to follow what Jed does and place them away from proposed openings (16" or so depending on the wall height).

I know they wall wants to crack at the openings but the joint tends to mess with the lintel above the opening especially when trying to drive wind loads through the wall. I don't know how people justify the wind loads at joints above openings.

I also know engineers who request the reinforcing not be continuous through the joint. They claim that it prevents the wall from shrinking properly however, this is not something I do.