K1TTT Technical Reference

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 United States.

 

1997 UBC (Uniform Building Code) -- used mainly west of

the Mississippi.

 

"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 ACI 318-99 Building Code Requirements for Structural

Concrete (which is referenced by all building codes in

the US) states:

 

"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