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
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?
AISC Design Guide #3 shows a L/600 vertical
deflection requirement (DL+LL). This is typically what we would use
for this case. I would not consider the joist DL as LL (not sure exactly
what you mean there)... but I would include the joist (and roof panel, etc.)
DL with the LL for the deflection calc.
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.
Most likely there is a cracking issue there.
This would warrant the L/600 or the 1 degree maximum rotation that AISC Design
Guide #3 recommends. Not that you are counting on the wall to be fixed
at each end but that each end is more fixed than a "pin" would tend to put
bending stress in the plane of the wall at the ends of the lintel beams.
Tighter deflection limits will tend to limit the end rotation that would cause
those end moments. My guess is that a masonry or concrete design
guide/code would address this situation...
Thank you for any guidance.