Multi-wythe Brick Wall Properties

[TRAK.Structural]

So I've got a project where I designed a 2-wythe brick wall with a grouted collar joint (total 10" thick). The design also called for horizontal joint reinforcing to connect the 2-wythes together, spaced at 16" oc. As luck would have it the contractor did not fill the collar joint nor did he install the joint reinforcing.

I'm thinking of using those retrofit wall ties (Simpson Heli-Tie, etc.) to hold the wythes together and make this wall act like a composite section. Does anyone have any resource/references for calculating the section properties of the wall assembly with no grout/mortar in the collar joint? The ties will have to resist the shear to force composite action so I think I could just use the material/section properties of the ties to check strength on that. Any other ideas?

 

[phamENG]

Those ties aren't meant to be used in shear. You might be able to, but you'd have to contact Simpson and see if they'll provide you with capacities. The only published load tables I'm aware of are axial loads only. You need that mortar/grout in the collar to give you shear capacity to call the wall composite.

I'd just take the capacity of the independent outer wythe and add it to the capacity of the independent inner wythe - no composite action.

 

[TRAK.Structural]

Pham - That's a good point. I can try to run the numbers that way but I'm doubtful that it checks out. Would probably have to use threaded rod and adhesive if I wanted composite action as a retrofit, but I'm not going down that road with an empty collar joint that all the adhesive would just spill in to.

 

[phamENG]

Who in NC is building double wythe, unreinforced brick walls these days? Or was this attempting to match historic construction? And where in NC?

It sounds like the contractor really screwed up on this one - hopefully it's not too tall and they can strip one of the wythes down and rebuild it with the necessary composite tie in.

 

[TRAK.Structural]

The wall is supporting an outdoor covered area attached to a home. Client wanted all brick and the loads aren't that big.

Wall is about 11' tall, and surprisingly after some quick number crunching I think it may check out. My biggest concern is lateral (wind/seismic) on an 11' tall vertically spanning unreinforced brick wall. Allowable flexural tension seems to be the limiting stress and I'm coming up with < 10 psi. That relies on taking the section modulus of each wythe and doubling it. Even though I'm not considering true composite action I think doubling of the section modulus does inherently mean that both wythes must deflect together, so the retrofit ties will be required to make sure that out of plane loads are "shared".

 

[phamENG]

Even though I'm not considering true composite action I think doubling of the section modulus does inherently mean that both wythes must deflect together, so the retrofit ties will be required to make sure that out of plane loads are "shared".

I agree with that.

 

[milkshakelake]

I have used those Simpson helical ties to tie wythes together when there's damage. I don't think there's any published capacity or testing data for that, but it seems to work empirically. Though I agree with pham that a better, robust way is to remove one wythe and redo it. That also absolves much of the liability from you instead of trying to hack a solution that has no published literature on it.

 

[TRAK.Structural]

There are published load values for tension/compression of the helical ties, just not shear for composite action.

 

[masonrygeek]

You can use the TMS 402/602 for non-composite walls in Chapter 5 as a guide, but since the ties are already in place, it might be a moot point. And it sounds like it is working out for you.