Torsion on LVL beam supporting brick
Torsion on LVL beam supporting brick
(OP)
I recently did an inspection on an 18 ft span beam lintel, most likely made of an LVL beam (Drywall is still in place). The beam is supporting half of a 2nd story, roof and brick. The brick is supported on a steel angle which in turn is bolted to the LVL beam. The beam is currently at a deflection of L/300 and the brick facade has cracked. There is also slight twist of the steel angle.
The questions are:
1) Is it allowed by code to support brick with a Pre-engineered wood beam? (Despite the fact that the criteria of L/600 deflection is respected). I could not locate on IBC2006 were this is addressed.
2) Do you have a good reference on calculating strength of a wood beam due to excentric loading, such as brick?
3) In repairing the beam, should we simply replace the wood with a steel tube beam, which then would require steel columns...
Any comments would be appreciated. Thanks,
ST
The questions are:
1) Is it allowed by code to support brick with a Pre-engineered wood beam? (Despite the fact that the criteria of L/600 deflection is respected). I could not locate on IBC2006 were this is addressed.
2) Do you have a good reference on calculating strength of a wood beam due to excentric loading, such as brick?
3) In repairing the beam, should we simply replace the wood with a steel tube beam, which then would require steel columns...
Any comments would be appreciated. Thanks,
ST






RE: Torsion on LVL beam supporting brick
RE: Torsion on LVL beam supporting brick
RE: Torsion on LVL beam supporting brick
A fire treated wood would then be allowed?
RE: Torsion on LVL beam supporting brick
The torsion on a rectangular shape = cM/At, where c is a coefficient which depends on the aspect ratio of the rectangle, M is the torsional moment, A is the area of the rectangle, and t is the length of the smaller side of the rectangle. This shear stress is added to the shear stress due to direct shear, and the total shear stress is compared to the allowable shear stress (for example, 290 psi for PSL).
But I have found the difficult part of designing a header for torsion is the end connection. Usually, several lag screws are required to transfer the torsion from the header to the king stud.
DaveAtkins
RE: Torsion on LVL beam supporting brick
RE: Torsion on LVL beam supporting brick
RE: Torsion on LVL beam supporting brick
One caveat is that there are LVL manufacturer recommendations that there be a moisture barrier between the masonry mortar and LVL. I suppose this is to prevent degradation of wood fiber and lamination bond at the point of bearing.
Hope this is helpful.
RE: Torsion on LVL beam supporting brick
So, do you all know how to evaluate the torsional deflection resulting on a wood or PSL beam?
RE: Torsion on LVL beam supporting brick
Try the following link for a basic treatise on the subject.
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RE: Torsion on LVL beam supporting brick
This is a residential house - therefore IRC applies. Also, the IRC allows brick veneer to be supported on steel angles attached to wood studs for instance (see Figure R703.7.2.1).
Supporting from a PSL (LVL or other) composite lumber should be OK provided the following:
1. The wood beam is designed for long term deflections and limited to L/600 or 0.3" (per ACI 530).
2. The brick sits directly on a steel angle and not on the wood itself.
3. The resulting torsion is taken into account (per DaveAtkins above)...and also considered for the design of the supporting end posts.
RE: Torsion on LVL beam supporting brick
Quite right about using IRC JAE. My mistake.
RE: Torsion on LVL beam supporting brick
In trying to calculate the expected rotation of the beam, remember that it is a summation of the amount the beam twists between the supports and the amount the ends rotate due to bending of the supporting posts. You can probably get a good idea of which component is most important by observing the way the brick is cracked.
RE: Torsion on LVL beam supporting brick
RE: Torsion on LVL beam supporting brick
RE: Torsion on LVL beam supporting brick
RE: Torsion on LVL beam supporting brick
I think you have to now remove the interior finish from the beam enough to expose the beam section, the end connections, and the connections of the shelf angle.
You said the deflection is L/300, so it looks like that is around 20 mm. Certainly enough to cause the cracking without any accompanying rotation, as there are no vertical control joints.
Part of the shelf angle deflection could be differential to the beam deflection, depending on the connection between the two.
RE: Torsion on LVL beam supporting brick
And, yes, I have a 24" deep brick fascade over my garage doors that is supported on 12" deep wood headers and 4x4 steel angles, but no kickers. I have no structural problems, but the span is only 8 feet too.
Mike McCann
MMC Engineering
RE: Torsion on LVL beam supporting brick
RE: Torsion on LVL beam supporting brick
Mike McCann
MMC Engineering
RE: Torsion on LVL beam supporting brick
I suppose installing a new column in the middle of the opening is out of the question?
RE: Torsion on LVL beam supporting brick
RE: Torsion on LVL beam supporting brick
The IRC also states that veneer above openings shall be supported by non-combustible materials (R703.7.3)
RE: Torsion on LVL beam supporting brick
RE: Torsion on LVL beam supporting brick
It is also interesting to note that a valley frames into the center of the span too. Was this a sudden condition or gradual? If sudden, was there a heavy snow that loaded the valley.
With that amount of brick above, the owner better seriously consider adding a central column to remedy the situation. Should they ever try to sell the place with out a fix, they are going to take a much bigger hit if it is not fixed than nessing up the exterior look. FUNCTION BEFORE FORM HERE - FOR SAFETY.
There were two 6.8 or higher earthquakes on the Western portion of the Pacific rim yesterday. A 7.2 off the Kuril Islands, and a 6.8 near New Caledonia. Is this structure in a high earthquake zone?
Mike McCann
MMC Engineering
RE: Torsion on LVL beam supporting brick
The contractor will probably provide a high estimate since, as I told him, there is no engineering design done yet.
RE: Torsion on LVL beam supporting brick
Then also check the end bearing on the header to the columns. If this is a gradual condition, it could be crushing the bottom of the beam, causing the gradual cracking. Torsional stresses may be the least of your problems here.
Mike McCann
MMC Engineering
RE: Torsion on LVL beam supporting brick
Yes - that's why you use a steel angle and ensure that there is a moisture barrier/separation between the exterior and wood beam - per LobstaEata's post (8th from the top).
RE: Torsion on LVL beam supporting brick
Find out what the beam actually is before you go to the effort of thinking about replacing it. Drywall patching = cheap. You and the other people spinning their wheels speculating = expensive. When you find out the beam overstresses post that....also find out how the angle is connected (lags or thru-bolts?)
RE: Torsion on LVL beam supporting brick
The LVL is part of the lintel, and the code specifically calls for veneer above openings to be supported by non combustible lintels.
RE: Torsion on LVL beam supporting brick
I believe you are correct...I stand corrected. Thanks.
RE: Torsion on LVL beam supporting brick
RE: Torsion on LVL beam supporting brick
Take a look at Figure R703.7.2.2 above, showing masonry veneer being supported on a steel angle and fastened to wood studs. The language contained in 703.7.3 (or at least a strict interpretation) seems to directly conflict with the associated figure on teh same page. It would be interesting to contact someone at the ICC to obtain a clarification.
RE: Torsion on LVL beam supporting brick
I went to a introduction of the 2003 IBC/IRC back in the day and the code official explained that if "it" doesn't fit in the IRC, then use the IBC. I'd say that masonry veneer on a steel lintel fit better with the IBC. In which case I'd go with the Section 2304.12 which says wood supporting 4" veneer is a go.
RE: Torsion on LVL beam supporting brick
RE: Torsion on LVL beam supporting brick
Mike McCann
MMC Engineering
RE: Torsion on LVL beam supporting brick
RE: Torsion on LVL beam supporting brick
2304.12 allows brick veneer to be supported by a wood foundation.
2104.1.6 rules out other uses, including lintels
RE: Torsion on LVL beam supporting brick
Any conclusions on this?
RE: Torsion on LVL beam supporting brick
If it's NOT done moving (i.e. a foundation issue) then you might spend $$ to fix with a nice heavy sttel beam only to have the crack open up all over again!
RE: Torsion on LVL beam supporting brick
RE: Torsion on LVL beam supporting brick
If you are designing strictly under the IRC, then it does appear that the LVL is a code violation (i.e. supporting masonry veneer over an opening per R703.7.3.)
The IRC does allow masonry to be supported by wood such as cases where an exterior wall turns back over a roof (per IRC Figure R703.7.2.1). But it explicitly says no to wood beams supporting masonry over openings.
Since you have a wood beam supporting masonry in violation of the IRC, your next step would seem to be to go to the IBC in accordance with IRC R301.1.3 where it states that "Engineered design in accordance with the International Building Code is permitted for all buildings and stuctures, and parts thereof, included in the scope of this code."
So as an engineer, you can go to the IBC as structurebeton mentioned above. So that then raises the question of whether wood beams can support masonry veneer in the IBC.
In the IBC - section 1405.5 indicates that masonry veneer must meet ACI 530. Also, section 2304.12 states explicitly that no masonry may be supported by wood.
ACI 530, section 6.2.2.3.3 states the following: "Provide noncombustible lintes or supports attached to noncombustible framing over openings where anchored veneer is not self-supporting..."
So the wood beam is simply not code-compliant.
RE: Torsion on LVL beam supporting brick
I would recommend cutting in a vertical expansion joint on each side of the overhead door, filled with sealant and a backer rod. I would consider adding a vertical EJ where the veneer steps up over the projection, to the left of the overhead door. I wouldn't do anything with the lintel.
DaveAtkins
RE: Torsion on LVL beam supporting brick
What I am a bit concerned now is that apparently wood beam lintels are illegal. The contractor will have a fit, and generally speaking, because they haven't seen that on a house they will think that I am not a qualified engineer.
RE: Torsion on LVL beam supporting brick
If this required a building permit, go take a look at the approved plans and compare them to what you have - bigmig is right, drywall is cheap, you need to know the existing conditions.
The building code official will tell you if they allow it, you can ask their opinion about common practice and if they think it's acceptable. Be somewhat obtuse, dont' identify your client or the house yet.
Please let us know how it turns out.
RE: Torsion on LVL beam supporting brick
If they say LVL's are OK, then I'd also be interested in how they respond to the code logic I posted above. It may be that the local code, as adopted, had amendments to the IRC that allow it but I wouldn't bet that would be true.
RE: Torsion on LVL beam supporting brick
I just find it hard to believe a steel lintel is required for your condition.
DaveAtkins
RE: Torsion on LVL beam supporting brick
RE: Torsion on LVL beam supporting brick
A piece of wood, when wet with high humdity as in Georgia - 90 to 95% extended at times, then drying out with a decrease in humidity, will develop a memory of the deflection it has seen and will not return to the original shape. This happens with varying load and varying humidity. The same phenomenon is used to advantage in the construction of wicker furniture.
This is not a problem that is going to go away on its own. It will continue long term. The installation of a steel beam would avoid this problem.
Mike McCann
MMC Engineering
RE: Torsion on LVL beam supporting brick
I believe they used an LVL or PSL to span 18 ft. However, I think it was not designed to suppport 1.5x dead load => Therefore, the beam has been subject to long term creep. I think LVLs are less subject to humidity conditions, don't they?
Anyway, when they uncover the beam header, I will see the real story behind...
RE: Torsion on LVL beam supporting brick
Some have said that it is common to have brick veneer over garage doors, but I think this instance is uncommon. You have a two car garage with one single door, a roof valley coming in over the door, varying height veneer, a lot of things to go wrong. The architectural design contributed a lot to this situation.
RE: Torsion on LVL beam supporting brick
RE: Torsion on LVL beam supporting brick
I don't think there are provisions preventing concrete or masonry support on timber structures. Certainly, there are a lot of existing examples, including lintels. There are a lot of old brick buildings here with hardwood footings. As long as the sapwood was removed and a durable species was used, they are generally still in good condition after 60 to 100 years. One species, called ironbark for good reason, was commonly used. Even the termites found it too hard. Most housing here was built with hardwoods until recent years, but now plantation pine is the preferred material with house builders. And now the termites are well fed.
Regardless of the supporting structure, it would be very uncommon here to use brick veneer over a double garage door. Lightweight cladding is used.
RE: Torsion on LVL beam supporting brick
Could it be the INTENT of the IBC/IRC is that wood members not support STRUCTURAL concrete/masonry, but that brick VENEER supported by wood is allowed? It seems to me that there is a difference.
True that falling brick veneer can kill, but that does not involve the structural failure of any main STRUCTURAL building component. If so, it needs to be clarified. If not, then maybe I'm reading more into the code than exists.
Mike McCann
MMC Engineering
RE: Torsion on LVL beam supporting brick
RE: Torsion on LVL beam supporting brick
In my experience (Aus, UK) no one would use timber to support brick veneer in a typical suburban home, especially over an 18' door.
Obviously it is more common in other parts of the world.
RE: Torsion on LVL beam supporting brick
Mike McCann
MMC Engineering
RE: Torsion on LVL beam supporting brick
RE: Torsion on LVL beam supporting brick
....The 18-foot garage door opening is framed with a 3-ply 18" LVL. The beam is supporting the second floor
bonus room, roof and brick loads. There are cracks in the brick directly above the center of the door, along
the right side, and above the door on the left. Our calculations indicate that the 3-ply beam is slightly
overstressed to meet the brick deflection requirements of L/600. Furthermore, it is our understanding once
the brick was removed to verify bolting of the steel angle, it was discovered that at some locations the
vertical leg of the angle was not in direct contact with the beam, but rather compressible material. We
recommend that the compressible material be removed from behind the angle and the angle be bolted
directly to the beam. In addition, we recommend installing a 2-ply 16" LVL directly under the floor joists
spanning past the existing door header king studs. The new beam will carry the second floor load,
removing the load from the garage header....
So, there was 2 issues: Undersized Beam, And Compressible material between the angle and the beam...
This still does not resolve whether or not it is legal to use wood as a lintel beam.
RE: Torsion on LVL beam supporting brick
RE: Torsion on LVL beam supporting brick
R703.7.3 - veneer above openings shall be supported on lintels of non-combustible materials.
RE: Torsion on LVL beam supporting brick
RE: Torsion on LVL beam supporting brick
If the building official will allow it, intumescent paint can be used to fireproof the LVL. If not PSLs are available with fire-retardant treatment.
Have you checked the deflection compatibility of 2-16" LVLs (I=1195) with 3 18" LVLs? (I=2552) There may be more load on the 18" LVLs especially since they are already preloaded with the dead load.