Brick veneer height 2

[EBF]

I have been reading some previous posts on this topic and I would like to get some opinions on a situation we are facing, that differs from the ones I have read about so far. We are designing a 2 story building with 15' story heights and a 3' parapet for a total height of 33'. The building is a steel frame structure and the exterior walls are brick veneer on steel stud backup (non-loadbearing). Question is: do we need to provide a continuous support angle hung from the steel structure at the roof level since the brick height exceeds the 30' height limit of ACI 530? I was planning to go ahead and put it in until I saw the significant increase in steel framing sizes to support the brick (we would have to locate the angle at the window heads, so we would need to support about 7' of brick). Any thoughts on this situation?

 

[BAretired]

Could you support the brick veneer at roof level and provide bracing for the parapet?

BA

 

[JAE]

This section has always made me angry as its wording is just poorly written.

Four ways to read the "English" here:

[blue]Option 1[/blue]
When the veneer exceeds 30 ft., you have to support any brick above 30 ft.

(unless it is part of a gable "triangle" up to 38 ft., where you don't have to provide additional support....but let's ignore the gable condition)​

If you don't have a gable end, then the 30 ft. limit requires you to support any brick above 30 ft. and at each story thereafter.
That means you'd have a 30 ft. height of brick off the foundation, then supports at each story thereafter including your roof level (i.e. every 15 ft. in your case).

[blue]Option 2[/blue]
When the veneer exceeds 30 ft., you have to support any brick above 30 ft. - supporting the brick at each story above it, unless you have a part that is a gable - up to 38 ft.
You could possibly read the intent here that short parapets that go a bit above 30 ft. don't need the support at the roof line as they are similar to the 38 ft. tall gable end.
If the parapets send you above 38 ft (or perhaps the average of 34 ft) then you'd have to add support at the roof.

[blue]Option 3[/blue]
Same as Option 1 but you only have to provide the support at the next story above 30 ft. (using the exact language of the text).
Since you don't have a "next story" you don't need to provide support at a story that doesn't exist.
So your parapet, even up to 38 feet,say, would be OK...as long as there's not another "story" above you.

[blue]Option 4[/blue]
It's Friday and the writers of this text were obviously drunk when they wrote it so do whatever you want.


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[bob33]

These old empirically derived requirements in our masonry codes are a nuisance, but they are based on years of experience. The concern in this case is the differential movement that can occur between the brick veneer resting at grade and the steel stud backup resting on each floor as well as the windows, control joints, parapet capping, etc.. My approach has been to engineer the elements and avoid shelf angles when possible. I have gone up to 55' with shear walled buildings when the architect allowed for my calculated differential vertical movements at the ties, windows, control joints and tops of walls. Where there are no windows I have gone much higher.

 

[masonrygeek]

Look at Bob33's common sense response here. The reason for the height limits for brick veneer isn't the need for vertical support, its for differential movement. The 30' limit is a guard against designers forgetting about differential movement. Using alternative design means you are exceeding the prescriptive limits and are "engineering" a solution to exceed those limits. So run some calculations to show the amount of differential movement to see what the difference between 30' and 33' would be. In some cases you have to detail around elements that penetrate through the brick veneer so that they don't restrain the movement you are designing for. A steel stud backing lessens the amount of differential movement since it doesn't shrink as compared to a wood stud backing/frame where the differential movement becomes critical - even at 30'-33'. BIA Tech Note 18 and 18A provide the guidance you are looking for (

http://www.gobrick.com/read-research/technical-notes).

BTW, The Masonry Society (TMS) is having their TMS 402 (ex ACI 530) code meetings this weekend in Salt Lake City. I'm sure there will be some drunk code writers tackling the very issue of veneer height. Come and join in!

 

[Ron]

Put a support angle at the 2nd floor line...meets code and will help your waterproofing of the cavity.

 

[milkshakelake]

It depends if you're trying to follow code or you want a good building. If you want a good building, it depends on the type of construction. Since you mentioned steel, I think it's fine. Differential movement won't be an issue. Theoretically, if it were wood framing, I'd be concerned with shrinkage of wood.

To add a counterpoint: I inspected a 7 story building that had brick without supports. The bricks were all f'd up only 3 years after construction. So after that experience, I started putting brick relieving angles at every floor for anything more than 2 stories. Maybe it's conservative, but the owners will thank me later. I read the brick tech note that masonrygeek shared, but I like to be conservative to protect my license.

 

[JAE]

I don’t think it is all about differential movement control. There was also mention some time ago that the issue involved the size or magnitude of individual “panels” of brick that could collapse in a fire to the street below.

By requiring story-by-story supports you were limiting sections that would collapse at one time. For steel studs the ability to maintain veneer Anchorage was better than wood.

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[EBF]

Thank you all for the responses, always great to hear other opinions. I read on a previous post that someone had received some comment from ACI that the reason for this provision was fire protection related. That would make sense since there is no limit on cmu or concrete backup and the Code commentary states that we still need to account for differential movement. I was interpreting this similar to JAE's option 3, no story above, so don't need to provide the vertical support. Just don't know if a building official would be convinced. I plan to discuss with the architect and then come up with a strategy. Thanks!