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RE: Rebar Spacers in PC beams

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My guess is that they are holding the spacers in place with tack welds. Are
they following all of AWS D1.4 in the welding of these spacers? In many
cases, they ignore code because "they are just tacks." Bad idea.

Bob Shaw
SSTC

-----Original Message-----
From: Michael L. Hemstad [mailto:hemstad.ml(--nospam--at)tkda.com] 
Sent: Friday, January 28, 2005 11:38 AM
To: seaint(--nospam--at)seaint.org
Subject: Rebar Spacers in PC beams

Glen Underwood wrote:

"I've designed a conventionally reinforced precast beam with two layers
of 
longitudinal tension reinforcement - specifically - 8 - #7's in two
layers 
of 4 each.  The design clear spacing between the two layers is 1".  The 
beam is 12" x 13" and will be a composite tee-beam when the slab is cast
on 
top.

The production crew has achieved the 1" clear spacing by placing a short

stub of #8 bar between the two layers of longitudinal steel.  This
happens 
every 5 feet or so along the beam length."


Glen,
This is fairly standard.  And yes, it may initiate some cracks, but with
that much steel in the bottom of a small (at least before they put the
slab on) beam, you're going to get significant shrinkage cracking before
any load gets on it.  This cracking will concentrate at these spacers,
but it's going to happen somewhere else if they're not there.  I
wouldn't worry about it.

Mike Hemstad
TKDA
St. Paul, Minnesota

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