Brick Shelf Angles 1

[miecz]

I'm posting this question for a friend, who writes:

We are working on a 60-feet high building, 4 levels with brick veneer/steel stud wall.

The BIA technical notes recommends shelf angles above 30-feet building height, unless the wall is rationally designed.

We are pursuing literature research to eliminate the need for the shelf angles. One reason is that the building structural steel is mostly fabricated.

We are considering several additional vertical control joints in the brick, particularly at the building corners and on each side of the windows. We have flexible ties to allow vertical brick movement. We are trying not to restrain brick as it grows.

Does anyone have any recommendations or suggestions for available literature that would tend to justify eliminating the shelf angles at each level?

 

[Teguci]

I recommend putting the shelf angles in. Unless the building is structural masonry, the shelf angles are required for differential movement.

 

[concretemasonry]

I would definitely recommend the use of shelf angles for the brick veneer.

Brick has long term irreversible expansion, while the steel structure does not. The angle are not just for brick support, but to separate the panels from each other so any movement can be allowed.

In the real world, the stiffness of the veneer may even be greater than that of the backup, so make sure the ties are proper to make things work together horizontally.

Once you get above the 40' mark, you are on thin ice. I have seen 20 story buildings properly designed that had excessive differences in elevation between the structure and the veneer, making windows a very big problem.

The BIA has seen many situation since brick veneer began to be used with a flexible back-up that can be subject to corrosion despite all the galvanizing and screw requirements. They are well experienced in the proper use of brick.

It is not just a structural situation, but you could be dragged into a future problem if someone allows a violation of a national recommendations.

Dick

 

[jike]

The brick will grow vertically and the steel will not, therefore, you need shelf angles so the brick growth can be taken up at each floor and will not accumulate in the upper part of the building.

Somewhere I have an article that estimates the growth per floor. On buildings with low floor to floor heights, shelf angles on alternate floors have worked!

 

[miecz]

Thanks for the replies. I understand that it's not prudent to go above 30 feet, and, would never have designed it this way. However, we came into the picture late in the game, so we're fishing for an answer. The phrase in the summary of BIA Technical Note 28B "unless the wall is rationally designed" caught our attention, and seems to imply that one could go beyond the normal limits, if some further conditions were met.

 

[jike]

Not sure if this article might help:

Tide, R.H.R and N.V. Krogstad, 1993, “Economical Design of Shelf Angles,” Proceedings of the Symposium on Masonry: Design and Construction, Problems and Repair, STP 1180, American Society for Testing and Materials, Philadelphia, PA.

 

[jike]

More references:

http://www.structuremag.org/article.aspx?articleID=911

Grimm and Yura, "Shelf Angles for Masonry Veneer", Journal of Structural Engineering, Vol. 115, No. 3, March 1989.

Parker, "Façade Attachments to Steel Framed Buildings", AISC Steel Design Guide 22, AISC, 2008.

Technical Notes on Brick Construction, Brick Industry Association,

http://www.gobrick.com.

18 - Volume Changes - Analysis and Effects of Movement, October 2006

18A - Volume Changes - Accommodating Expansion of Brickwork, October 2006

Tide and Krogstad, "Economical Design of Shelf Angles", ASTM STP 1180, ASTM International, 1993.

MSJC Code (TMS 402-08/ACI 530-8/ASCE 5-8) Building Code Requirements for Masonry Structures, The Masonry Society, Boulder CO.

 

[miecz]

Thanks again. This is such a great resource.

 

[Gumpmaster]

Take a look at ACI530-05/ASCE5-05/TMS402-05 paragraph 6.2.2.3.1.3 (that's a mouthful) and the surrounding paragraphs.

It has maximum shelf angle spacings depending upon the wall type (wood stud vs. steel stud). The most you can get out of a steel stud wall is 30ft (38ft at a gabled end). After that you need to provide shelf angles at every floor.