control joints @ large openings

[Prestressed Guy]

I have a project that has three 40’ long walls with a pair of 14’-8” openings and returning walls at each end. (See attached elevation)

This project is in a high seismic area (SDS D) and the piers are designed as shear walls with bond beams at 16” o.c. with hairpins at each end. The walls are also load bearing. There are 32” deep lintels above the windows with 2-#5 top and bottom and the chord reinforcement bond beam and top of parapet bond beam above that.

I cannot see anywhere to put a control joint in these walls so I am inclined to put no control joint in these walls. Opinions?

 

[Prestressed Guy]

I have an additional question. Does anyone put a control joint in an opening in a load bearing wall? I am thinking that it might be possible to put the joint at the center of the opening. The shear is minimum and if the bottom reinforcement is continued across the joint it will not affect the tensile reinforcement.

 

[concretemasonry]

Is this a through-wall CMU masonry structure or a structure of some type with a masonry veneer?

Where are you climate-wise?

As a seat of the pants suggestion (not a recommendation without more information), I would suggest control joints just off the openings and at an appropriate distance from the corners. Just a detailing suggestion.

Dick

 

[Prestressed Guy]

This is an 8” CMU load-bearing wall. The walls also resist all lateral forces and are designed as Special Reinforced Masonry Shear walls.

The project will be located in northwest Washington State and the climate is temperate but damp. The site gets 20 inches of rain annually with temps between 30 and 80 degrees.

When you say “just off the openings” I assume that you mean into the jamb rather than over the openings. I had thought about that possibility but how would you deal with the 2’-0” required minimum development of the lintel bottom reinforcement. This would also interfere with the tension rebar for the shear piers.

I am attaching a 3d view of this section of the building.

 

[BAretired]

From your description, I am not too clear on this but I don't believe you need any control joints in these walls.

BA

 

[msquared48]

I have to agree.

Mike McCann
MMC Engineering

 

[Prestressed Guy]

Thanks for the look at this.

Most of the articles I find on control joints talk about putting control joints at locations where the wall changes height or at the edge of openings but all of the examples they have show the joint in the middle of a big section of full wall. No one ever wants to show the tough stuff.

With all of the reinforcement I need at my openings it doesn’t make sense to put a joint there. I am attaching a view of where I plan to put my joints. Any comments or suggestions?

 

[dik]

You might consider putting the joints to the left of RE and to the right of RF. The large openings, in particular at the corner, combined with the large wall between them would be a source of cracking.

Dik

 

[steellion]

Control joints at wall openings will help control cracking at the corners. CJ's also change the load path though. You can't rely on a triangular load distribution with arching action if you put a CJ at the wall opening because there is nowhere else for the load to go. Based on the sketch, that doesn't seem to be an issue because there isn't enough wall above the opening to get a triangular distribution anyway. Have the CJ come up at the end of the lintel bearing, and assume the full weight of the wall above is acting on the lintel.

 

[Prestressed Guy]

Thanks for the comments Steelion.

I had considered putting a joint at the side of the opening. In the attached sketch the two possibilities are the blue line and the red line. I don’t like either one. The blue line run right through the anchorage for a cable suspended awning. The red one doesn’t leave much wall for the out-of-plane lateral forces at the jamb. It seams to me that the amount of reinforcement will keep the crack width to an acceptable level and that the joint are not needed.

I think I will put a CJ at the intersecting walls at RE and RF as DIK mentioned.

 

[BAretired]

What is RE and RF? I don't see those labels on the drawing.

BA

 

[Prestressed Guy]

Thanks for the look BA.

The grids are on the elevation in the original post. On the 3d views these grids are at the section of the wall that extends 4 feet beyond the walls with the large openings.

I would rather not put a CJ at these intersections if it is not needed. I am thinking that because the section is so much less at the lintels, most of the stress due to the shrinkage will be concentrated there. Given the amount of reinforcement required for the lintel design the cracks should be tight enough to avoid problems. This is especially true due to the lintels being grouted solid up to the diaphragm bond beam which is continuous in any case.

 

[BAretired]

Okay, duh...now I get it.

BA

 

[Prestressed Guy]

Thanks BA.

Do you or anyone else see a problem with enliminating the control joints at the intersecting walls at grid RE and RF given the amount of reinforcing?

 

[BAretired]

Haydenwse,

There is a potential for cracking at the end of your heavy reinforcement. Reinforcement does not continue through the intersecting walls, so a control joint at the exterior face of that wall would seem a good idea.

BA