When to use steel lintel or a CMU lintel 1

[Jim508]

Hello,

I'm looking for guidance on steel lintels vs CMU lintels. I need advice as to when to use either and the pros and cons of either. Any help is appreciated.

Best Regards,

Jim

 

[Archie264]

I've been required to use CMU lintels when the fire protection engineers told me they wouldn't allow exposed steel. I don't know what the codes say regarding that topic so I just take them at their word.

If that's not an issue than steel angles can be quite handy when installing openings in existing brick or CMU walls. That's because the steel angles can be sized to support each wythe of brick or each 4" of CMU, depending on specific circumstances, of course. Sometimes this can be done in a manner that precludes the need for temporary shoring.

 

[UcfSE]

Typically CMU or precast lintel for new construction.

Steel lintel for existing construction (though precast is possible), and steel lintel in new construction when a cmu or precast simply won't work. There are other situations as well, I'm sure.

 

[a2mfk]

I think it depends on what is most common in your area, and the preference of the contractor. In Florida for the most part pre-cast concrete lintels are the most popular, but there are some pre-engineered inverted-T type lintels that I see around too, like these:

http://www.powerssteel.com/lintels/

I am speaking about 8 and 12 inch load bearing CMU here, not for brick support.

It has been a while since I designed a CMU building with split-face, but it used to be you would have to form and pour those or use a steel lintel.

 

[AELLC]

Here in the Phoenix area, contractors much prefer Powerssteel lintels for new CMU construction.
I am a bit skeptical about their tabulated capacities and tend to de-rate them about 15-20%.

 

[XR250]

@Aellc;
I just did a job here in NC where the contractor wanted to use the Powerspan. Never had heard of 'em before. I typically use I-beams with plates, pre-cast or double angles. I derated them by 50% due to the lack of special inspection. The design values still seem a little suspect. Fortunately, I built in some additional factor of safety as well.

 

[a2mfk]

Why the skepticism of manufacturer's tables? I don't have a horse in the race, just curious as to your reasoning.

I assume to get Code approval all manufacturers these days have to offer quite a bit of proof their product does what they say it does. I know in Florida it is no joke to get something approved. When it comes to allowable loads of a steel lintel, there should be no proprietary black box vodoo, pretty straightforward structural engineering, no?

 

[AELLC]

The load tables seem to rely on composite action of the steel lintel and the CMU, and the tables with a top (compression) rebar in the CMU show even much more capacity. I never saw the actual calculations.

 

[a2mfk]

AE: Gotchya... Specifically looking at the Powers - PowerBox lintels, there are deformities/dimples that I can see in the photographs for composite action I assume. Probably would make us all feel better if there were some shear studs or something, but that would jack up the cost of manufacturing quite a bit.

I have always specified pre-cast lintels, but I will keep this all in mind if I run across steel lintels. A little bit of differential expansion/shrinkage along that grout-steel interface and you may lose some of the bond and composite action. But they do have many years of use and I assume they had to do a lot of testing?

 

[cvg]

powersteel apparently has CTS in Tempe on-board as structural engineer so it would seem just call them up and ask for documentation on the lintel design. Currently working with Turley and he seems to be pretty well respected around here.

 

[kylesito]

One advantage to steel lintels is speed of construction. They simply get set and the masonry continues. At most, the mason takes a coffee break and when he comes back he is able to continue his work. With masonry lintels, they must be shored before they can be built. This causes delays in the schedule.

PE, SE
Eastern United States

"If a builder builds a house for someone, and does not construct it properly, and the house which he built falls in and kills its owner, then that builder shall be put to death!"
~Code of Hammurabi

 

[azcats]

Agree with above. I've seen contractors use the PS lintels essentially as permanent forms when CMU lintels are specified on the drawings. It's reinforced and grouted as a typical masonry lintel and the composite action is ignored. Works great when there are lots of short to medium span openings.

And CTS are good people who I'm sure would be happy to provide you with data. I spent a couple years there right out of college. They had some interesting work utilizing these lintels and post-tensioned masonry walls in residential structures as well as freestanding post-tensioned masonry walls.

 

[a2mfk]

azcats- good idea, if you have doubts, throw a bar or two in there and design it as a traditional lintel and the Powers lintel acts as a form at a minimum.