Notes on Welding Re-Bar
Barry:
I wrote a response to your
original post but I guess it
is somewhere in the ozone....
I think a general discussion
of Welding Reinforcing
Steel is necessary. I think
I have responded to this in
the past but this should cover
the full spectrum of this
issue.
Reflectorites should be able to search on
the subject
now and get a decent answer...
The Welding of Reinforcing
Steel in concrete is covered
by the several building codes
used in the
1997 UBC (Uniform Building
Code) -- used mainly west of
the
"1903.5.2 Welding of reinforcing bars shall
conform to
approved nationally recognized
standards. Type and
location of welded splices and other
required welding of
reinforcing bars shall be indicated on
the design
drawings or in the project
specifications. ASTM
reinforcing bar specifications, except
for A 706, shall
be supplemented to require a
report of material
properties necessary to conform to
requirements in UBC
Standard
19-1."
UBC Standard 19-1
19.101.1 "..........,
the welding of concrete
reinforcing steel for splices (prestressing steel
excepted), steel connection devices,inserts,anchors and
anchorage details,as
well as any other welding required
in reinforced concrete
construction, shall be in
accordance with the Structural Welding
Code --
Reinforcing Steel, ANSI/AWS
D1.4-92..."
What this says that if you
want to weld normal
reinforcing steel which is normally
ASTM A 615 grade,
you need to follow the
requirements of the AWS D1.4 for
electrode specifications, min. weld
size, type of weld
and most importantly the
preheat requirements... I
believe that this is 300 degrees F
for a minimum of 20
minutes prior to welding.
If you use ASTM A 706 reinforcing bar then no preheat is
required for welding.
However note that the intent
of welding reinforcing
steel is focused on direct
splices and connections to
other metal devices to be
embedded in the concrete, not
for rebar cage assembly or tacking
in lieu of wire ties.
The
Concrete (which is
referenced by all building codes in
the
"7.5.4 -- Welding of
crossing bars shall not be
permitted for assembly of
reinforcement unless
authorized by the engineer."
"R 7.5.4 -- 'Tack'
welding (welding crossing bars) can
seriously weaken a bar at the point
welded by creating a
metallurgical notch effect. This
operation can be
performed safely only when the
material welded and
welding operations are under
continuous competent
control, as in the manufacture of
welded wire fabric."
As an aside I looked the
topic up in the 1996 BOCA Code
and the 2000 IBC(International
Building Code) and they
both refer to AWS D1.4 for
welding and ASTM A 706 as a
weldable reinforcing bar.
There you have it.. The codes do not want you to tack
weld the tie bars in a rebar
cage, but if you must use A
706 bars and use the
procedure in AWS D1.4.
Use wire ties for your cages.. I have been practicing
structural engineering for over 30
years and have yet to
see a problem with using wire
ties for field assembly of
reinforcing bar cages.
Concering the 5 foot set back from
your house foundation
I'm a little confused by
this. A few questions are in
order;
What is the frost depth in
your location?
What type of house
foundation do you have (stem wall,
pier)?
How deep is you house
foundation?
Do you have a basement?, if so, How deep is it?
With this knowledge then a
case could be made to move
the foundation closer to the
house. I don't understand
the 5' for 5' depth concern.
With respect to your
question if the bid amount was
reasonable. You do not give enough
information on what
exactly was bid and where you live
and what the
prevailing wage wage
and rental rates are. I would say
that off hand it is on the high
side of typical but not
out of reason. Better
information gets a better answer.
Hope this helps you, again I
don't know what happened to
my first response. All the
best
73
Hank Lonberg,
P.E./ S.E., KR7X