brick deflection

[structuralnerd]

For brick veneer, do you usually limit your horizontal deflection to l/600 for your backing material or can you limit it to the standard l/300 for drift? I have a situation where I am using wood studs as backing, and it is getting to be difficult/expensive to limit it to l/600. Any thoughts?

 

[Lion06]

We always use L/600. You could easily get cracking if you use L/360.
The drift is the floor to ceiling displacement (not midspan deflection).
Even for drift, we typically stay in the H/500 range.

 

[lkjh345]

Typically I use L/600 for the back up studs, though I went to a seminar a couple of years back where one of the speakers was from BIA and he said that L/480 was acceptable for deflection of exterior brick cladding.

Haven't been able to bring myself to use L/480, but just throw it out for you consideration.

 

[Lion06]

One other thing to keep in mind. While we don't do it, AISC does talk about using the 10 year wind for serviceability issues (deflection of the back-up). Depending where you are, it is probably in the 0.7*50-yr wind range. Look in the Design Guide on Serviceability for confirmation of the 10-yr wind approach. If your 50-yr wind is based on 3 second gusts and your V = 85-100 mph, then your 10-yr wind is 0.71 times the 50-year wind. If your V>100 mph, then your 10-yer wind is 0.53 times the 50-yr wind (this one has a minimum of 76 mph - still a lot less than 100).

 

[Tdog67]

The L/600 has always been a vertical deflection limit. We usually stay in the L/480 range and don't forget for component & cladding deflection calcs you can use 70% of the load per the IBC code.

 

[structuralnerd]

I've been looking through the code, and I cannot find the section in IBC that talks about the 0.7 factor. Can you point me in the right direction? Thanks.

 

[DaveAtkins]

I am OK with using L/360 when I use full wind load. This equates to about L/514 when using 0.7 WL (which is found in IBC Table 1604.3, footnote f).

Brick veneer has a fair amount of flexibility.

DaveAtkins

 

[lutein]

From what I understand, brick deflection limit of L/600 comes from BIA Tech Note 17B for lintel beam. If you are talking about vertical drift of frame, which implies theoretical zero at base and drift X at top, then Height/300 should be applicable due to the cantilever nature. The infill wood backup which spans between top and bottom will still have to be designed for H/600 due to the simple span nature.

For servibility, we could reduce to 10-year interval wind using table C6-3 in ASCE. Note that the factors from the table need to be power of 2, because V is in power of 2 for the pressure coefficient. For a typical wind region, <100mph, the factor is 0.84, using 0.84^2 = 0.71, which almost equal to AISC's 0.7 factor. These 2 factors should not be used simulataneously.

With all of these being said, most pre-engr buildings w/ brick veneer are designed w/ drift limit as low as H/240, which does indeed meet requirements, because H/600 X 0.7 (for 10-year) X 0.5 (for cantilever) = H/213. I personally do not use this limit, but just seen it on drawings.

 

[JKW05]

BIA Tech 28B has L/600 for metal studs. Can't see why it would be different for wood.

 

[Einsteim]

We've typically used L/600, but I have seen specifications that allow L/480. Remember though, you really need to consider the L and how much of a span that really is. L/600 for an 8' tall wall is significantly less than a 30' tall wall.

 

[JAE]

l/600 for our usage.

 

[Lion06]

I believe BIA also limits the deflection (vertical) to 0.3" for lintels. I am not sure if that carries over to horizontal deflection of backup, but I wouldn't see why not.

 

[MikeE55]

I agree with DaveAtkins. If you look at "Serviceability Design Considerations for Low-Rise Buildings" by AISC, they are actually very liberal with horizontal deflection requirements. L/600 or 0.3" max are for vertical deflection only.

 

[csd72]

I would stick to the L/600. Larger deflections may result in cracking of the masonry, particularly with veneers which have minimal compressive load.

If you are using IBC then technically you can use 70% of the wind load for serviceability, hopefully that helps.

 

[miecz]

See the December 2004 Issue of Structure magazine. It includes an article that references the Western States Clay Products Association Design Guide for Anchored Brick Veneer over Steel Studs. According to this article, WSCPA vaguely suggests limits of L/360 or L/600, depending on performance levels. Level 1 (L/600) appears to be intended for high level of quality, and long service life, as is normally required for public or institutional buildings. Level 2 (L/360) appears to be intended for good level of quality, and average service life of general office, industrial, and residential buildings.

 

[strguy11]

I use 70% of the wind load for an L/600 limit. StructuralEIT has it correct.

 

[JLNJ]

h/360 for me.

I guess that makes me a "liberal".