From: Scott Maxwell <smaxwell(--nospam--at)engin.umich.edu>
Date: Tue, 22 May 2001 11:45:05 -0400 (EDT)
I would hazard a bet that if no intermediate joints (besides the ones at
the end of the beam) are supplied, then mother nature/the physical world
will provide them (i.e. by some cracking). A wall that is 8 ft tall but
50 feet low is bound to have some cracking due to the aspect ratio. 50 ft
is just a little too long without a joint, in my experience.
On Tue, 22 May 2001, Fountain Conner wrote:
> Let me throw a tidbit or two in here...
> *If* the wall above the steel beam is continuous, w/o openings, why not
> ...using it as a simply supported beam with the masonry in compression and
> the steel working in bending *and* as tension steel in a "deep" beam.
> You can shore the steel beam until the masonry is placed and cured. You
> can fill and reinforce the block cells, etc., and make a composite section.
> Your deflection can be slightly lessened, but this will be somewhat offset
> by creep.
> Of course, you can accomplish the same thing with a less-vigorously
> reinforced masonry wall and a fairly heavily reinforced "bond" beam at the
> top for the "top flange" of this monster.
> Another possible solution (probably the most practical) would be a "poured"
> concrete lintel. The depth/span ration should be okay. This sounds like a
> parapet wall. Can you brace down from the top to the roof structure?
> Otherwise you're trying to cantilever from a "pinned" connection.
> Control joints in the beam span have been mentioned. I think they are a
> bad idea. A joint at each end will take care of the rotation. In the rest
> of the span, the masonry will be in compression (If you shore during
> construction). And masonry in compression is not given to cracking.
> My 2 cents...
> Fountain E. Conner, P.E.
> Gulf Breeze, Fl. 32561
> From: Javier Encinas <jencinas(--nospam--at)coqui.net>
> To: seaint(--nospam--at)seaint.org
> Subject: Re: Steel lintel beam
> Date: Monday, May 21, 2001 5:27 PM
> A 50-ft long simply supported beam with such a high load (8' x 70 psf = 560
> plf) and deflection limits (L/600) would be a monster. I rather would
> suggest to form an 8-ft high vierendel truss, either in steel or concrete.
> The open spaces could be filled with block and plastered. This way the
> members would be much lighter and the deflections smaller.
> Javier Encinas
> ASDIP Structural Software
> ----- Original Message -----
> From: edjonson
> To: seaint
> Sent: Monday, May 21, 2001 10:58 AM
> Subject: Steel lintel beam
> I have a question about using a wide flanged steel beam for supporting an
> opening in a masonry wall. The opening is 50 feet, with 8 feet of masonry
> wall above. I'm planning on using a steel beam, designed as simply
> supported. I have two questions.
> 1. What deflection limits should I use for the steel beam? Also, should
> the dead load from the roof joists be considered as live load?
> 2. If I design the steel beam as simply supported, is there a potential
> problem with cracking in the masonry wall due to negative bending stresses?
> I have a low roof that frames in to the side of the masonry wall at the
> same level as the steel beam that will lateral support the steel beam.
> Thank you for any guidance.
> Ed Jonson
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