w section w bottom plate lintel

huangyhg

w section w/ bottom plate lintel
i'm designing a lintel to span 28'.  it supports 5' of 8" blk. centered on the beam and 5' of face brick at an eccentricity of 6".  there is some roof load but very little. i want to use a w16 section w/ bottom plate.
i find that a cont. 3/8" plate is adequate to support the brick if the plate is designed to act as a cantilever (fixed end at the connection to the bottom flange).  if welding is frequent, is it unreasonable to assume that this an adequate assumption.  
the torsion calculation apprears to be very lengthy.  i got the aisc design guide 9 for torsion.  5' of brick acting at 6" doesn't seem like it will be a big problem.
is it normal practice to provide brg. plates with anchors at the brg. locations to help resist the torsion at the ends of the lintel? i will provide some rebar welded to the top flange at 4' o.c.
does anyone have experience with a similar situation?  i don't feel comfortabledealing with torsion.
any help will be appreciated.
thanks.
a wide flange will twist quite a bit (very little torsional stiffness) unless you brace it externally to some other element.
we have even gone to using tube sections with the bottom plate to increase torsional stiffness.  you still have to torsionally restrict twist at the ends.
as jae states that you still have to take out the twist at the ends. you might want to consider framing into steel columns at each end.
i think jae's point is that you should calculate the twisting angle and resulting vertical brick deflection and that you'll probably find that it's no good.  folks often calculate stresses and stop there.  as he hinted, a tube will work better.  i'd actually be very surprised if you can get anywhere close with any w16.
correct-o-moto 271828.  i was in a hurry.  watch the twist on wf shapes as they would create high bending in the wall - and produce cracking in the masonry.
hey, that reminds me of something.  
i think in some situations, the cmu can keep the beam from twisting.  i usually put 6" headed studs on the top of the w-shape.  with the right boundary conditions (that don't always exist), i think wall bending could provide twisting restraint.
no clue if the op's situation does this, but it's something to think about.
i agree with all the advice above.  wide flange is no good for torsion.  you have to either get the beam centered under the load or use a closed section to resist the torsion.  any chance of using a concrete beam?  
hey - i've done that before - used a series of vertical, deformed bar anchor or weldable rebar welded to the top flange and extended up into grouted cells in the cmu.
this was an attempt to engage the wall out-of-plane stiffness.  the couple formed by the rebar and the face of the block wall would tend to prohibit twisting of the beam.  hard to measure its stiffness and the resulting bend in the wall so i try to avoid having to do that.
thank-you everyone for your responses.
the architect prefers that w sections be used so that it can infilled with block.
i will add 16" long rebar welded to the top flange (at 32" o.c.) of the beam to restrain the twisting.
i'm concerned because the span is so great (28').
would stiffeners at frequent intervals (40") on each side of the web work?
i can use plates on the outside to create somewhat of a box shape.
any comments about sizing the plate? fixed end cantilever o.k.? i'm not considering bending in the long direction.
the plate cantilevers off the bottom flange. that will not be your problem.

stiffeners perpendicular to the web will do little to increase the beam's torsional capacity.
don't be too quick to jump at the advice 271828 and jae that you may be able to depend on the wall to prevent twisting of the beam.  as 271828 says, it depends on the boundary conditions.  i think that would require a substantial load on the wall from above, and you don't have that.  the rebar on the top flange may help somewhat to limit the lateral movement of that flange, but i think in your case it might even accentuate the lateral movement of the bottom flange.  you need to consider that the architect's preference at this stage won't help you if the beam rotates and the brick falls off.
if you can use plates to create a box shape, then i think you are home free, provided you have a way of resisting the twisting at the ends of the span.  but i thought the architect was insisting on stacking block between the flanges.