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nhstruct (Structural)
10 Apr 12 20:51
I have a wood framed project with 4" brick veneer. The veneer bears on a shelf on the foundation wall and extends 42' tall. Per code we can only go about 33' without needing a releiving angle. Has anyone attached a relieving angle for clay masonry brick to wood framing. Neither me or my boss have a good feeling on attaching the releiving angle to the wood, and it will likely increase our header sizes to maintain an L/600 deflection and the releiving angle. The wall construction is 2x6 at 16" o.c with 1/2" exterior sheathing and 3" cavity between the sheathing and rear face of the veneer.
concretemasonry (Structural)
10 Apr 12 21:50
What code has a 42" height limit between vertical supports or relieving angles?

Normally, brick veneer usually is limited to 2 stories height between angles, but some codes or architects allow more. It sounds like you have the classic 3" +or- cavity for rigid insulation and an air space for circulation and flashing.

Dick

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

RFreund (Structural)
10 Apr 12 21:57
You are right in that you header size would increase. In empirical design the ACI 530 says not to support masonry with wood however you can do it if you design for it. You must consider creep which can on the order of 2.5x short term deflection. Can you locate the relief angle at a different elevation than your headers? Another concern may be that the wood may shrink while the the masonry is expanding. Here is a decent read on relief angles: http://www.structuremag.org/article.aspx?articleID=911

Also another discussion on masonry deflection:
http://www.gobrick.com/portals/25/docs/technical%20notes/tn31b.pdf

ACI 530 supporting unreinforced masonry = L/600 and 0.3, reinforced limits do not apply. Section 1.10 commentary

Deflection of walls out of plane held to 0.007. Test by SEAOSC/ACI committe rcommended 0.01h. (See RMHB 6.5.3.I)

I don't think I've really answered your question but maybe this is helpful.
 

EIT
www.HowToEngineer.com

focuseng (Structural)
10 Apr 12 22:15
Done several of these.  You would be right to be conservative and check the size of the relief joint for shrinkage of the wood structure.  All headers should be checked for their deflections too as you mentioned.

The treatment would be very similar to any shelf angle but you have a wood connection and the bearing of the backside of the shelf angle on wood backup.  A lot of time this may be lag screws into studs (not my favorite). Extra safety factor for fastener bearing creep here may be in order, YMMV.  If you can get the joint at the floor deck for some real meat into a extra beefy rim-joist that is maybe a good way to go. Also then the rim will provide some extra stiffness for the headers downstream. Some concern for quality installer here and don't forget those vertical joints too in your flexible tall masonry wall.  I usually spec out better masonry ties and spacing too on these tall wall with wood backup especially around the window openings.

MAP  
hokie66 (Structural)
10 Apr 12 22:17
Is that 33' limit a code requirement or just a recommendation?  I would much prefer the 42' tall veneer to be supported vertically at the footing level.  There are too many issues involved in supporting relieving angles and masonry on timber framing.  I have an old Brick Institute of America Technical Note which suggests limiting the self-supporting height to 100'.

Your title says "Stone veneer", but you then go on to talk about a brick veneer.
concretemasonry (Structural)
10 Apr 12 22:47
The 33' is probably a prescriptive code requirement. Other jurisdictions may have other prescriptive requirements.

The reason is the fact that wood frame shrinks and most clay or stone products do not, so there is a differential in the end that can tear apart flashing and interfere with with window openings. Clay poses a more severe problem because it has a long term EXPANSION that is opposite to the wood shrinkage. Most prescriptive codes are written for categories of materials and stone or clay brick that are lumped together to arrive at the common industry standards. Temperatures also have an effect on the local prescriptive requirements.

The 33' limit fits the typical wood frame/masonry apartment building.

Dick

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

nhstruct (Structural)
11 Apr 12 7:29
Thank you for the responses, the 33' limit is what we found in ACI-530. We have not determined exactly where the releiving angles will go yet, but we are thiniking we will need one at the 3rd floor level, and 4th floor level. As the code also recommends only 12' tall of brick when supported on wood framing. Part of our concern is that the floor is going to be constructed with wood trusses (top chord bearing), and due to the span we need the full width of the wall to make the bearing work, so we will only have a single or most likely a double ribbion board inbetween the trusses.  focuseng you siad that you have used lag screws before, our concern woth lags is that over time they could rip out of the wood as it expands and contracts. Our thought was to use thur-bolts, but since the holes are slightly bigger than the bolts, we are concerned that the angle is going to rotate with and the wood expands and contracts. one though was wo us LSL ribbons as these are more stable and will experiance less expansion and contractions, thus leading to a better connect. typically when we have a situation like this we put a steel frame on the first floor and pick up the brick from there, since when support on steel code allows up to 30' tall, but this architects hates using steel for anything but first floor framing between the garage and 1st floor.
hokie66 (Structural)
11 Apr 12 7:36
Again, is this a law or a recommendation?  Your best solution is to support the gravity load of the veneer wholly at the footing level.
nhstruct (Structural)
11 Apr 12 7:46
Per code ACI530 Chapter 6 Section 6.2, height limits above non combustible foundations is 30'-0" to top plate and 38'-0" to top of gable with wood framed backing. In our case we do not have a gable as it will be a mansard roof set-up
MiketheEngineer (Structural)
11 Apr 12 16:31
1 and 2 story brick veneers done around here all the time - resting on foundation shelf..  Just make sure they are well "tied" to your wall..
RFreund (Structural)
11 Apr 12 17:11
The idea behind the relieving angle is only to help the expansion of the masonry veneer and the shrinking of the structure. As explained the article I previously posted the brick will not crush. As far as bolting and rotation - won't the angle be sandwiched against the rim board? How would it rotate?

EIT
www.HowToEngineer.com

hokie66 (Structural)
11 Apr 12 17:21
Mike,
He is talking about 42' tall, about a 4 storey building, I imagine.

 
concretemasonry (Structural)
11 Apr 12 18:02
The spacing of reliving supports (with "soft" joints)has been documented for decades and is not a structural requirement/situation but a serviceability point that affects the use of dissimilar materials that move differently in a multi-wythe wall.

I saw a 6 story building where the casement windows on the upper floors (no relieving angles obviously)could not be opened because of the differential heights between inner structure and the exterior clay brick that went through the predictable long term expansion. This was one of many problems that created the inclusion of relieving angle spacing in ACI 530.

Dick

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

focuseng (Structural)
11 Apr 12 19:27
If you can get the shelf angle at the rim locations then you might consider a double "L" where one is inverted from the other or other similar configuration with a plate welded on.  The shelf angle can then be installed like a top mount hanger flange on the top plates of the wall where the joist sit.  You will have bearing issues at the wall for your joists vs the top mount flange but I can see this overcome with some creative effort (spaced top flanges).  The only downside to this may be the heat sink factor. I'll draw a picture if you don't get this.

I also appreciate your concern with the lags not holding over time but In my experience this has not been an issue with good contractors.  Why is this any different than a deck ledger on a house? OK, maybe not the best example:) The deck is certainly be a more troubled situation.

One other thought is to install a wood ledger under the shelf angle as a backup fastener in addition to the shelf angle fastening.  This may mean more air gap at the veneer but another thought nonetheless. - Similar to when doing a wood beam supporting masonry I put down a steel angle on top of it and then the masonry goes on.
shobroco (Structural)
11 Apr 12 19:34
42' is not terribly excessive for height of self-supporting masonry, & I'd never support more than a nominal amount of masonry on wood framing so I think you're far better foregoing the angle.  Our code (Ontario) doesn't permit supporting any masonry on wood without some pretty thorough proof that it won't deflect or crack.  A big issue in your height will be the differential shrinkage though, as a couple of guys have pointed out; I've seen shrinkage of wood framing in 2-storey buildings cracking the glazing because there was no room at the masonry sills.
MiketheEngineer (Structural)
12 Apr 12 12:27
I have to get NEW GLASSES - thought he was working with 42 inches!!
focuseng (Structural)
20 Apr 12 16:53
Just ran across this reference in an alternate search for something.

In ACI530-02/TMS402-02:
Chapter 6, Veneer
   6.2.2.3.1.5  Exterior masonry veneer having an installed weight of 40 psf or less and height of no more than 12 ft are permitted to be supported on wood construction when installed in compliance with the provisions of this Chapter. A vertical movement joint in the masonry veneer shall be used to isolate the veneer supported by wood construction from that supported by the foundation. Masonry shall be designed and constructed so that masonry is not in direct contact with wood. The horizontally spanning element supporting the masonry veneer shall be designed so that deflection due to dead plus live loads does not exceed l/600 nor 0.3 in.

Also note that Table 6.2.2.3.1 gives height limits from foundation for masonry veneer backed by wood of 30 ft at plate and 38 ft at gable.
Hope this helps somebody.
hokie66 (Structural)
20 Apr 12 17:15
Just wondering...when did the American Concrete Institute become the Authority on supporting brick masonry on wood framed construction?
JAE (Structural)
20 Apr 12 18:20
hokie66,
The MSJC is a joint committee comprised of The Masonry Society, ACI, and ASCE.  They put together the MSJC document which has call numbers for each participant.  ACI's is 530.

The combination of these groups is due to the fact that the MSJC has both clay and concrete masonry units included in the code/specification.

 
hokie66 (Structural)
20 Apr 12 19:33
Thanks, JAE.  Now I understand.
concretemasonry (Structural)
20 Apr 12 22:19
The ACI is not the authority on masonry veneer. The ACI has the staff and publishing contacts to coordinate, print and distribute the documents, which is something that the TMS, BIA and NCMA do not want to get involved with.

When the "masonry code" also known as ACI 530 was written, it was recognized that an engineer could structurally easily support very high (up to 10 stories)veneers, it would not perform well from a practical standpoint.

The problem that creates the established (perhaps arbitrary in some cases) limits is that not all veneers and structural systems have the same properties. Clay brick has long term expansion, concrete masonry has some shrinkage, natural stone is relatively neutral, concrete frames shrink, steel has little creep and wood shrinks a great deal. Because of the various possible combinations an arbitrary (and reasonable) limit a vertical spacing was selected to provide a workable limit and still allow windows to function and opening to be flashed to create a functional structure with some form of compliance with an established standard. Without a reasonable limit a great engineered support system for veneer could be a disaster if the differential movement between the veneer and structure is too great, the entire moisture barrier/flashing could be destroyed and useless and the wall would be considered a failure.

If an engineer wants to micro/over-engineer a specific combination of structural system and a veneer system and sign off on it, it could be acceptable, but costly.

Dick

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

JAE (Structural)
22 Apr 12 15:42
Well - the limits also had to do with very high continuous veneers not performing well in a seismic event.  Six or more stories of veneer loosing their support or stability when only supported at their base is much more catastrophic than individual sections of 12 ft. tall veneer falling.
hokie66 (Structural)
22 Apr 12 18:43
JAE,
But the limits quoted...30', 33', 38'...don't seem to relate to that logic.
concretemasonry (Structural)
22 Apr 12 19:13
There are really two separate situations to consider.

JAE is completely correct that the connection of the veneer to the back-up, is a structural problem compounded by the height and weight of the veneer, hardware used and the supporting system. This is definitely in the field of a structural engineer.

The second is the practicality of the veneer to perform as desired for functionality and not just structurally.

Veneers and back-ups are not always compatible from an expansion/shrinkage/creep standpoint because of the variable materials (natural, fired clay, concrete) when the frame shrinks and the veneer expands/shrinks to where the windows would not open or function. This is why the spacing of relief angles for veneer ended up in ACI 530, which is based on the needs of the MJSC regarding the use of masonry materials.

The ACI 530 document is rightly looked on as the most authoritative masonry structural code, but it also includes many other practical requirements to prevent people from looking only at the structural aspects. When the group (MJSC) was formed, there it was known that a wider view of masonry was needed and reflect the different properties on veneer materials, mortar, grout and possible back-up systems that could reasonably provide some practical standards. Since the members on the committee usually had multiple masonry interests, memberships and activities, the logical place to provide the information was in ACI 530, which in many ways is a consensus standard as evidenced by the MJSC (Masonry Joint Standards Committee).

Dick

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

JAE (Structural)
22 Apr 12 20:12
hokie66, what I've always seen in the MSJC is that they limit the foundation-to-top of veneer height to the 30 ft. limit to accommodate 3 story wood framed apartment buildings that are very common in the US.   

In a major seismic event, I suppose 30 feet of falling veneer would be a bad thing.  But to limit high-rise construction they force the designer to support the veneer at various levels to partition off the sections, allow them to move a bit relative to the supporting structure, and allow only portions of the veneer to fail at one time instead of the whole height.

 
hokie66 (Structural)
22 Apr 12 20:27
I'm not arguing for supporting great heights of brickwork without relief.  I've never actually done even a three storey building in wood, and don't like the idea of going higher.  On concrete buildings with brick veneer, we always support the brick at each floor, or at most, alternate floors.  And I certainly recognise the window flashing issues that concretemasonry talked about.  The situation I had in mind, and maybe that doesn't correspond to the OP's question, is a brick veneer, without openings, full height.  In that situation, and in properly detailed cases with openings, I would rather support a 40' high brick veneer on the concrete footing than on wood bearing walls.
JAE (Structural)
22 Apr 12 20:28

Quote:

On concrete buildings with brick veneer, we always support the brick at each floor, or at most, alternate floors.

I typically do too.   

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