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Old 07-15-2013, 12:09 AM   #1
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Steel channel for lintel


I'm installing (or trying to) a new 9 foot long triple pane PVC window but due to height of ceiling issues 2x10 joists above my window is not an option. The wall is 7'9" and is a load bearing wall supporting the trusses on a single story house with 26 foot trusses (including 1foot beyond each wall). The trusses are a tri bearing design and directly below the truss King post will be a partition of which will be costructed as a load bearing wall to reduce the load on the load bearing walls supporting the trusses. This wall is also directly above the main girder supporting the center point of the floor joists. A worse case (snow load) uniform load of 250-270 lbs per foot is being used and my lintel has to be a maximum height of 5 1/2 inches. The top plate of the wall is a double plate and the wall has a stud spacing of 16 inches OC with 2x6" studs, including top and bottom plates. It has been suggested to use a standard C5x6.7lb/foot steel channel with a 1/2 spacer under the channel with plates welded on the ends to bolt the channel to the side studs of the window frame and from what I was told this channel should be able to handle 400 lbs/foot load. There will also be a Fir 2x6 placed beside the channel as a nailer as well. My question is should I consider using an I beam or am I worrying too much about nothing? This was a concern when I unloaded a 20 foot section and noticed how springy it was over this 20 foot span under its own weight.

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Old 07-15-2013, 02:29 AM   #2
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Steel channel for lintel


Someone says that the channel will carry 400lbs/ft? That figure is meaningless. There are several parameters which need to be checked when
using a steel section. The most critical in your case will be deflection.

The channel could well support a lot more than 400lbs/foot (if it was suitably restrained from buckling sideways) but your concern will be how much deflection you can accept. If, say, you allowed 1/2" gap over the unit frame, would that be sufficient to allow for the deflection under maximum snow load? Only an SE could check that for you.

A second consideration you need to watch is the fixing of the beam at the ends. I might haave mis-read this, but if you are welding plates on the ends, there will not be much space to get two bolts/screws in. And remember that there will be minimum spacings for the bolts/screws in the timber itself, otherwise that will be over-stressed.

Channels have their uses but as beams there is always the tendency for lateral buckling. In this respect, an I-beam is more efficient.

Designing a narrow beam on a 9ft span is really a job for an SE. It might work OK when fitted, but under maximum snow load......?

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Old 07-15-2013, 03:42 AM   #3
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Steel channel for lintel


Tony thanks for the reply! It was an AE that suggested this and local building codes departments gave guidelines for worst case loads such as heavy snow loads which we had last winter. The suggestion was angle irons on the ends for anchoring to the side studs and then I thought about a 1/4 inch steel plate like 5 1/2x 4 to allow room for the nailer. Then there was the thought about bolting through the parallel flanges to the top plates on top and to the top of the window frame at the bottom of the channel. Then of course I wondered about bolting it directly to the 2x6 Fir nailer but IF that is done a great deal of caution because that can weaken this channel especially if the holes are not centered in the middle so this is probably not a viable location for bolting. I will have to discuss this with the engineer some more. It is amazing how difficult it is finding imformation on channels.
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Old 07-15-2013, 08:46 AM   #4
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Steel channel for lintel


Quote:
Originally Posted by Hennmann View Post
I'm installing (or trying to) a new 9 foot... window but...
The wall is 7'9" (high) and is a load bearing

...should I consider...
How low in the RO the window can be set? Yeah.
Two or more smaller openings in that 9 foot span? Yeah

In short... you need to find a practical compromise or two
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Old 07-15-2013, 09:05 AM   #5
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Steel channel for lintel


From the floor? About 18 inches. If what the engineer said is correct and his calculations indicate 1/4 inch deflection at 400 lbs per foot but as Tony mentioned IF IT IS PROPERLY INSTALLED. The deflection is a major concern and I was planning on a minimum gap above the window unit of 1/2+ inches. On the other hand a 10 lb per foot 5 inch I beam can carry 660lbs per foot and deflect the same amount..........so the story goes.
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