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RE: REPOST: Steel Lintel Bearing on Masonry

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Mike:

I am in agreement with most of your comments re: lintels.

A couple questions come to mind:

Where the angle is supporting the brick veneer, do you require the cavity
to be grouted at the bearing to support the angle? or does the Architect
return the brick to provide the angle bearing? The Architects prefer to
leave the cavity open to prevent cold transfer but we need the support for
the angle.

I like the simplicity of the HSS and eccentric plate. Are you using
stiffener plates at say 32" oc to stiffen the eccentric plate? If you are
taking the torsion into the tube, it seems that it would be difficult to
take it out into the masonry at the bearing. With an 8" CMU backup, are
using the brick and block together to resist the torsion (up force on the
block and down force on the brick) with anchor bolts resisting the tension
into the block?

Jim K.



-----Original Message-----
From:	Michael L. Hemstad [SMTP:hemstad.ml(--nospam--at)tkda.com]
Sent:	Monday, February 25, 2002 4:13 PM
To:	seaint(--nospam--at)seaint.org
Subject:	REPOST: Steel Lintel Bearing on Masonry

Dave,
Most of what I have to say about lintels is pretty basic, but, for what
it's worth:

1.  For CMU, the beams need to be in multiples of 8 inches.  I suppose you
could make a 12 inch beam work with a half height (4 inch) course, but it's
usually not worth it.  (Like I said, pretty basic.)

2.  For openings of maybe 8 feet or less, we usually have a choice between
CMU bond beam and steel beam with plate.  The bond beam is fireproof and
rustproof, but you can look up and know the steel beam has been placed.
 We've also had problems with masons substituting block with knockout tabs
for the typical U-shaped bond beam block.  The reinforcing ends up in the
middle of the block instead of at the bottom.  Our Structural Notes now
forbid this for lintels, although we permit the knockout block for
continuity bondbeams (e.g. at the top of a wall).  "Forbid" is a relative
term, of course; it assumes someone reads the notes, and then follows them.

3.  Any time we have brick to support over more than about 4 feet, we use
an HSS section with an eccentric plate.  For 4 feet or less, we usually end
up talking ourselves into a galvanized angle for the brick.  I'm not aware
of any problems with this, but I won't claim it's the greatest because we
usually end up bearing it on the brick.  I'll wait for the flamers to nail
me for this.  The bigger openings, or unusual brick overhangs (e.g. fancy
corbeled cornices) cause concern for overturning of the beam at the
reactions.  We bury a steel column in the wall rather than try to carry
this into the CMU.

4.  We try very hard to hold deflection to less than L/600.  This helps a
host of problems, edge-bearing overstress being high on the list.

5.  We don't assume arching of the carried masonry.  Too many times, the
architects have thrown an extra door or window in at the end of a wall,
believing our details will still work and invalidating the arching
assumptions.

6.  As previous posters have said, lateral loads are an issue.  An HSS
usually performs a lot better than a wideflange.  A related issue is
unbraced length; we consider the beam unbraced.  If the lintel is carrying
an interior wall, unbraced length may matter more than the nominal lateral
load required by code.  If you have something to dump lateral load into, of
course,  it can also brace your beam.

7.  For spans longer than about 8 feet, we deal in steel or reinforced
concrete beams.  A few years back, one of my supervisors, now retired, put
a concrete beam over a sixteen foot opening in an otherwise steel framed
building.  The contractor went nuts, because he had to bring a trade back
for just one item.  On the other hand, the concrete beam has the same
advantages listed above for the CMU bond beam: it doesn't need fireproofing
and it won't rust if exposed.

8.  You mentioned openings up to 30 feet.  This, in my experience, is pr
etty big.  Any span close to this will require columns at the ends of a
large steel beam.  You still need to try hold deflection down to L/600.

9.  Some engineers weld rebar dowels on top of their lintel beams.  I've
never decided whether this is worthwhile or not.  I suppose it is if the
wall above takes lateral load, and the beam has to resist it (as opposed to
dumping it into a floor slab).  It does make shipping difficult.

10. Our bearing plates are usually just a continuation of the 5/16 inch
plate shelf, primarily because it's simple.  This has the disadvantage of
potentially causing stress concentration at the edge of the opening.  It
hasn't proven a problem for us, primarily because of the stiffness we
design into our beams and the use of columns for longer spans.

This is all I can think of in one sitting (...and 15,000 engineers breathe
a collective sigh of relief...), and I really haven't addressed your
question.  No, we don't get too excited about therrmal expansion gradients.
 We're more concerned with holding the lintel in place.

Mike Hemstad, P.E.
TKDA
St. Paul, Minnesota
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