From: Roger Turk <73527.1356(--nospam--at)compuserve.com>
Date: Mon, 21 May 2001 17:48:00 -0400
50 ft *clear span*????
Deflection limits: L/600 per UBC 2106.2.9; L/600 but not more than 0.3" per
ACI 530. I go along with the ACI limits.
With only 8 feet of wall above the lintel, you will not be able to take
advantage of arching if the span *is* 50 ft, therefore all the wall directly
above the lintel should be considered as loading. My criteria to take
advantage of arching is that the wall has to be 1/2 the span "plus a little
bit" above the lintel. (The "little bit" is to provide a compression area for
the arch.) Windows and any wall penetrations will also limit when you can
take advantage of arching. (Remember that windows and doors are frequently
filled in when remodeling, so don't be too precise on reducing your dead load
based on openings. I neglect all openings when considering wall loads.)
Cracking will be the result of deflection, not negative moments. You can
frequently see triangular cracks in masonry walls above lintels.
Dead load from the roof joists will be dead load to the lintel. Why would
you want to consider it live load? It's there all the time, isn't it? It
isn't moving or movable.
A. Roger Turk, P.E.(Structural)
Ed Jonson 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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