Loose Lintel for Brick Veneer 1

[cedent]

I am having a few issues with the loose lintels on a building project. The architect is showing 6" metal studs + 5/8" sheathing + 2" Rigid Insulation + 1 1/2" air space + brick veneer. This means that the total distance from outside face of sheathing to outside face of brick is 7 1/8". This leaves me with the need to update my lintel schedule on the job. I have sized a L7x4x3/8 lintel on a maximum opening width of 5'-0".

Limiting the deflection to L/600 and tip rotation to 1/16", I am finding that this L7x4 is right at it's limit. I'll have to have the architect move his joints off of the edges of the windows to ensure full arching action.

I am fortunate that I don't have any larger openings on this metal stud back-up.

My question is this: Have any of you encountered a similar condition? (This is the largest cavity I've seen. The architect tells me the new energy codes are driving this.) If so, are you moving away from loose lintels?

Thank you for your time and help.

 

[BAretired]

I would have thought a 4x4x1/4 L would have been more than adequate for a 5' span. Why are you making it 7" wide?

BA

 

[cedent]

The architect wants the vertical leg against the sheathing - which is a condition we have been seeing at our firm a lot in the past 5 years.

I think the reason has something to do with flashing.

 

[BAretired]

I thought that the cavity behind a rainscreen was supposed to be vented top and bottom. The architect is cutting off air circulation with his detail.

BA

 

[hokie66]

I would never support brick on the end of a 7" leg. You need to be concerned about the structural aspects of the building more than the architectural.

 

[msquared48]

And what would be wrong with placing the required insulation between the metal studs?

Batt insulation would work well here...

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[cedent]

As stated in original post, I have checked stress, deflection, and toe displacement due to rotation.

I am no expert on this part, but Current energy codes apparently require a certain amount of continuous insulation in addition to the batt insulation.

My primary question was whether or not you are seeing these types of details and finding them just as restrictive. I have seen these details on jobs for years now... though not quite as extreme as this. I have also compared our details to those of peers on several occasions... when the opportunities present themselves. Again, those situations were also a bit less extreme than the one I am describing.

 

[msquared48]

I have not run into this situation before, but...

I would use a tube steel section as the window/door header within the studwall, perhaps with tube steel columns at the ends, then weld the ledger of the size needed to the tube steel header. The tube steel section is great for torsion...



Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[SteelPE]

Couldn't you have the fabricator weld a plate to the backside of a smaller angle?

 

[Ron]

Hey hokie66....AMEN

As we all know, architects make it pretty....we make it work.

 

[JAE]

Ron,

Rather: Architects provide the template for asserting efficient form and vernacular to impress the human response into a view of the emerging tectonic visualization and the effects of materiality on praxis.

Engineers make it work.

 

[msquared48]

You an Architect wannabe JAE?

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[bookowski]

I agree with BA's comment - this seems like a bad architectural detail. If the reason is energy code it seems counter-productive to disrupt the rigid insulation with the angle, a thermal bridge, not to mention the disruption of the cavity drainage plane.

Also, how do you check tip rotation? Maybe I'm off here but with the angle so offset the end bearing will only be at the outside of the legs, the vertical will be hanging out in space - not much torsional restraint there.

 

[nhstruct]

I actually Have a project going now with a 7 3/8" cavity. We needed a relieving angle to pick up 3 stories of brick we ended up with a L8x7x3/4" angle (from memory i don't have the plans in front of me) We have wood stud walls, so ended up putting steel columns in to support the lintels. The cavity was done mainly to get the insulation in as you noted.

 

[XR250]

I don't get it either. The ones I have worked on had the insulation run up behind the brick.
FWIW, I think in most situations, the lintel just acts as formwork until the mortar cures and then the brick acts as a deep beam. I know we don't design as such, but I think this represents reality. Otherwise, we would see many more issues with brick veneer over large openings. One thing you can do is specify joint reinforcing in the first couple of courses of brick which tends to make it act like a reinforced masonry beam. I heard this from an engineer at the Brick Institute of America.

 

[cedent]

bookowski,

I've modeled it several ways. I started with a beam model. Then I worked up a quick solid model in Femap/Nastran so that I could measure the tip deflection relative to the deflection at the vertical leg. I only constrained the part of the angle that would be embedded in masonry on each side of the opening.

 

[dik]

The wall construction isn't bad... can be supplemented with batt insulation. Bad overall detail.

The loose lintel is the problem and it shouldn't pass throught the rigid insulation to the sheathing. In these environs, the angle against the sheathing could easily be at a temperature of -30C... As BA noted, it should be bearing on the ends of the adjacent veneer and his L4x4x1/4 would likely be OK.

Dik

 

[concretemasonry]

The steel stud (wrinkled tin) is the major factor in the thermal short-circuiting compared to the lintel. The studs can reduce the FG theoretical wall "R-Value" by 50%, which is the major factor and is not important to structural concerns.

If you have gravity concerns. brace the lintel for a short period to allow the real load on the lintel be reduced by the structural properties of the masonry above., but I defy anyone to calculate the exact amount.

Going 2 stories between relieving angles is common, but going 3 or more creates problems creep/expansion with long term deflection of different materials (steel vs clay), but that is really an architects problem to control cracks and window leaks/alignment.

Dick

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

 

[Hokie93]

I strongly suspect that what the architect REALLY wants is to have a member closing off the cavity above the windows. We locate our steel lintel angles with approximately 3/4" clearance to the back of the brick (that provides adequate clearance for the flashing) and weld a piece of continuous flat bar or a small continuous angle to the back of the lintel angle to close off the cavity. This detail works structurally and makes the architect happy.

 

[OHIOMatt]

From what I know ASHRAE 90.1 is driving this whole issue. It is incorporated into the IBC by reference. This standard now provides minimum continuous insulation values as well as a total insulation value. It looks like the majority of the time you will need both cavity and continuous insulation.

I have dealt with this on one project to date, but it looks like that was just the beginning.