Masonry Control Joints 4

[pelotoner]

I understand that typical masonry joints are at 24' on center in a wall. However, how does that impact the rest of the structure?

ie... A 500' long building that has 12' tall masonry exterior walls for a pre-engineered metal building. There is a tie beam at the top of the wall that is spanning between metal building columns. For joints at 24' o.c., how does that impact the concrete beam? Is all of the temp/shrinkage transferring to the tie-beam? What about the Z-purlin continuous along the top of the wall?

Aren't we just preventing the stair-step crack and placing more stress on another element?

 

[OzEng80]

Shear connections (unslotted) are provided at the centre of panels to allow for movement and still transfer shear.

My reference is more to tilt up construction with a roof diaphragm instead of floor diaphragm but the concept is still the same...

 

[haynewp]

I have never seen the deck angle connected to transfer shear at only the center of the shear panels but I like the idea. I have seen hundreds of roof to tilt panel connections and they were all welded directly to embed plates spaced along the panel at like 4 ft on center. Never any restraint problems that I heard of.

 

[OzEng80]

They may have slotted connections at the rafters. Providing restraint along a panel is less likely to be an issue as restraining two panels together.

Hokie, in a much earlier post you said your company provides CJ's 4m from corners. Is this for wall shrinkage or slab shrinkage? If it is for slab shrinkage say no more but if they are for wall shrinkage - i tend to think of returns as 'releases' to shrinkage rather than 'restraints'. Would you provide shrinkage joints in a wall stepping in and out every 5m?

 

[hokie66]

OzEng80,

I can't honestly tell you why. The specification has been around for a long time, and I didn't write it. But like you, I see it as a restraint release for slab shrinkage. I think it is intended to apply only near the extremities of slabs where the restraint problems are worst, not at any steps along the way.

 

[apsix]

Beware the short return; see link.

As long as the step lengths are not too short or too long there should generally be no need for joints.

 

[pelotoner]

It seems that slotted angles only work for flexible diaphragms. We also do a lot of non-composite concrete floors w/ metal deck over bar joists; these composite floors are poured over the tie beam of the masonry walls.

For rigid diaphragms, would you try to isolate the walls, and put shear transfers at each masonry panel?

 

[csd72]

A very quick google gave me this:

http://www.maconline.org/tech/design/movement/movement.html

Typically the ties between the masonry and the structure are flexible enough to allow the in plane movement.

The fewer the joints, the more movement there will be at each joint.

 

[pelotoner]

It seems that providing a flexible connection from a rigid diaphragm to bearing walls, yet still transfer shear, would be difficult.
We don't seem to have problems in Florida, so I'm curious how you northerners provide that connection?

 

[hokie66]

apsix,

Your reference applies to brick growth, and we were talking primarily about concrete block. But in some cases, you could get the same stiffness problems with the forces in the opposite direction.