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Re: Steel lintel beam

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Section 1.10.1 of the 1999 MSJC (masonry code) states (section number is
different in older MSJCs, but content is essentiallly the same):

"1.10.1 Deflection of beams and lintels
Deflection of beams and lintels due to dead plus live load shall not
exceed l/600 nor 0.3 in. (7.6 mm) when providing vertical support to
masonry designed in accordance with section 2.2 or Chapter 5."

Note: Section 2.2 is allowable stress design for unreinforced masonry and
Chapter 5 is empirical design of masonry.

The purpose behind this provision, at least as I understand it, is
primarily to prevent cracking in the masonry as the beam or lintel
deflects.

Now the debate that I have heard is which dead loads should be included in
the deflection check.  Some argue that is should be ALL dead loads while
other suggest that it should only be those dead loads that are imposed
after the masonry is constructed.  The gray area in these discussions
usually is the weight of the masonry itself.  Some argue that, depending
on how the masonry is laid, the grout might "soft" enough to accomidate
the deflection of due to the weight of the wall.

Ultimately, you might want to be conservative and just use all the dead
load.  This will likely result is a BIG steel beam since more than likely
the 0.3 in. will govern.

You should include the roof joist dead loads as dead loads, but those dead
definitely should be included in the deflection check.

As far as the negative bending, I would say that "yes" there will be
cracks in the masonry at the ends due to negative bending if you do not
detail for it.  I would suggest, at a minimum, you will want expansion
joints (CMU) or control (brick) joints at the transition from lintel/beam
supported to masonry wall supported that will allow for this movement.
You will also probably want at least one or two joint in the middle of the
span.

Scott


On Mon, 21 May 2001, edjonson wrote:

> 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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