Not Using Brick Relief Angle

[RFreund]

Has anyone not used brick relief angles for say 4-5 story building, framed with either steel stud bearing walls or structural steel frame?
It seems like the relief angles can really add to the cost of your structural steel (obviously). My first question is that the requirements in the new 2013 MSJC code seem odd.
First, I thought there was some language about if the differential movement was considered than relief angles are not required, however the code seems to plainly state that if steel stud backup is used then 30' is your max height (38' at gables). Did this verbage disappear?
Next, when they say "back-up" of cold formed steel studs, does it matter if they are load bearing or non-load bearing? I thought differential movement was the issue here so if they are simple infill studs and the structural frame is steel or concrete, does that make a difference?
Third here are my considerations if you were to omit the relief angles, any other suggestions?
CFS Bearing Wall System
[ul]
[li]1/8" per floor for "squashing" of the tracks[/li]
[li]Temperate expansion of masonry add to:[/li]
[li]Expansion of veneer due to moisture[/li]
[li]Neglect axial shortening of studs due to strain.[/li]
[/ul]

Structural Steel System
[li]Temperate expansion of masonry add to:[/li]
[li]Expansion of veneer due to moisture[/li]
[li]I suppose include axial shortening of studs due to strain.[/li]
[/ul]

As a rule of thumb they say to consider 1/10" per 10'.

Has anyone done this? Is it a problem for the architect to deal with say up to a 1/2" differential on his top floor windows?

I have neglected wood because there would be quite a bit of differential due to shrinkage etc, but same argument I suppose.

Thanks!!

EIT

http://www.HowToEngineer.com

 

[jike]

The brick will expand due to taking on moisture while the frame and back up will shorten under load. These opposing movements can literally tear the structure apart if intermittent relief is not provided. For low floor to floor heights, brick relief is generally located at every other floor. For high floor to floor heights, brick relief is placed at every floor. It is NOT advisable to ignore these requirements.

 

[concretemasonry]

The reason for relief angles is because the brick have a long term expansion (even without moisture), while most structural systems have long term shrinkage, or are neutral at best.

If the relief angles get separated too much, you can expect window leakage and problems. - Especially in the future.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[RFreund]

I get it, I mean I understand the reasoning. I suppose, I'm just wondering if it is truly that difficult to detail around and can you actually "ignore" these requirements. Meaning is there somewhere in the code that allows you to detail for the differential movement? There can be quite a bit of shrinkage in a 5 story wood building, but we manage to detail around this (although we are not using brick, so this issues are a bit different). There seems to be much less differential movement with brick veneer in a steel building.

EIT

http://www.HowToEngineer.com

 

[KootK]

It would be nice to know the numbers that may have gone into the 30' rule. That rule is often apples to wood buildings that shrink significantly concurrently with masonry swelling. It seems reasonable to assume that a cold formed steel building, lacking most of the shrinkage, could go a fair bit higher.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[dhengr]

Rfreund:
I agree with Concretemasonry regarding the need for relief angles for brick veneer. I doubt that the codes will ever cover every imaginable condition and detail in the universe and they will probably never replace some engineering knowledge, judgement and experience. Although, they certainly are trying their damnedest to put an exact number on everything. Brick masonry expands with age and moisture so you have to account for this. Steel doesn’t shrink/shorten much over time or under load, so the differential movement is mostly the fault of the brick. Concrete and concrete masonry, and wood do shrink over time and during curing so the differential shortening is compounded by the different action of the two materials. You really can’t avoid this. It is a matter of judgement and experience as to how far you can push this issue. Architects do all kinds of things to make buildings and construction expensive, all in the name of their inflated design egos and what they think is sexy. And, not using shelf angles is a damn poor way to help them try to save some money. It will be your fault if it goes wrong. I’ve done these calcs. and made those judgements a number of times on my own projects, and even more times, after the fact, on projects which where having masonry problems of one sort or another. There are some good papers and masonry tech notes out there on these issues. Otherwise, let us know when you get your new details worked out which resolve all these issues, we would all be most interested in the newest way to handle them. While 3 stories sound about right for a max. height btwn. relief angles, I would doubt that there is some profound set of calcs. behind the 30'. Different bricks will react slightly differently, so each situation will be slightly different.

 

[Ron]

There are several reasons to use shelf angles....some structural, some not so much.

Depending on your interpretation of ACI 530 and other codes, you can almost rationalize not using a shelf angle for heights above 30 feet, particularly if you consider that the brick veneer acts as a deep beam. ACI 530 provides 30 feet as the prescriptive requirement absent further analysis. This link gives a pretty good exercise in several considerations of design of the shelf angle....

Shelf Angle Design-Structure Magazine

There are also some constructability issues that make the use of a shelf angle more practical. The shelf angle provides a "ground" whereby the masonry subcontractor can pull straight lines (rolled angle is straighter than wiggly running bond bricks!), both horizontally and vertically. This allows for a more consistent look to the brick and helps prevent "waves" in the finished wall.

Next is waterproofing. This is a cavity wall (rainscreen) design, typically. This means that water collects in the cavity and then exits through weep holes. The shelf angle provides a good support and logical exit point for through-wall flashing. Don't forget to yell at the architect to provide appropriate waterproofing protection for your brick ties and shelf angle.