[TowerTalk] Tack welding rebar, need howto

Sat Jan 4 12:38:45 EST 2014

Interesting tidbit from some Googling:

".... reading a rebar should go something like this:

The first symbol is a "production mill symbol." It is usually a letter. 
The examples would be an "NN" for Newcor Nebraska, "NU" for Newcor in 
Utah, "L," most likely stands for Latvia.

The next symbol is the rebar size. This is stated in numbers. The 
example would be a #4 rebar would be a typical half inch in diameter, a 
#6 rebar would be a three quarter inch diameter, and the equation 
continues as every eighth of an inch in diameter is considered an added 
number to the rebar's diameter.

Let's try a really big example for numbering rebar by size. A #18 rebar 
would be two and one quarter inches in diameter. The size of rebar 
mentioned in your question was a #6, which is three quarters of an inch 
in diameter.

The next symbol to look for on the rebar is the billet symbol. It should 
be the capital letter "s" and refers to "steel billet." Here is the part 
of the answer where I hope to explain the differing pull out behaviors 
you mention. The tensile strength of the rebar will be stamped next. It 
may be a grade 40 or a grade 60. The grades 40 and 60 refer to the yield 
strength respectively, 40,000 psi and 60,000 psi tensile strength....

The final marking on the rebar is the country of origin. This will be 
spelled out and should be self-explanatory. The examples would be 
Sweden, Latvia, Mexico, or my favorite, a domestic produced rebar with a 
small mill stamp on it and no country of origin stamp at all...."

I've never seen ANY markings on Home Depot rebar, but admit I haven't 
thoroughly examined a 20 footer.

Grant KZ1W

On 1/4/2014 6:02 AM, Patrick Greenlee wrote:
> A very robust cage you have there, David.  Could you site where the 40 
> times diameter is written?  I learned by watching and asking questions 
> of contractors and was told 25 times diameter by more than one and no 
> other value. I will have to look for a reference as I have no 
> alternate experience. Thanks for mentioning 40 as that provides 
> incentive to do some research. Oh by the way... although I demand code 
> or better whenever possible in all endeavors the only inspection I 
> have had building two houses and installing a tower has been by the 
> DEQ (Department of Environmental Quality) who inspect and permit 
> septic systems (my installer was lisc to self inspect.)
>
> Patrick NJ5G
>
> -----Original Message----- From: David Gilbert
> Sent: Friday, January 03, 2014 10:44 PM
> To: towertalk at contesting.com
> Subject: Re: [TowerTalk] Tack welding rebar, need howto
>
>
> That's not really true.  The "standard" building code (which varies of
> course from by application and jurisdiction) requirement is for splices
> to be a length 40 times the diameter of the rebar (I looked it up since
> my last post), which means a minimum 20 inches lap for 1/2 inch rebar.
> A "slight" overlap doesn't cut it no matter what you tie it with.
> Inline overlaps need to bite into enough concrete to hold both pieces
> together ... otherwise it's just wasted steel.
>
> More to the point of what I was trying to describe earlier, Tee
> connections for rebar are probably the weakest possible joints if not
> welded or hooked.   For a 2-dimensional example, picture the perimeter
> of concrete slab.  You have a length of rebar running around the
> perimeter of the slab roughly three inches from the edge of the slab,
> with some other pieces of rebar from side to side running across the
> interior.  Those cross pieces have virtually zero contact area to the
> perimeter runs, and they can't extend very far beyond the perimeter
> rebar because there is only three inches to the edge of the slab. Yet
> those cross laps are the only thing other than the internal tensile
> strength of the concrete itself (which if that were worth a damn we
> wouldn't need rebar anyway) keeping the edge of the slab from breaking
> off in the vertical plane of the perimeter rebar.  Since I don't trust
> welds made to uncertain compositions of steel (you can also research
> that topic online if you want), I suggested bends to make hooks ...
> which are in fact required by code when using concrete and rebar to make
> a beam. There is more to making rebar connections than just having them
> hold together during the pour.
>
> Lastly, someone also mentioned that welding rebar joints was desirable
> to hold the shape of the cage during the pour.  I don't think that's at
> all necessary either.  The rebar cage for the foundation of my tower was
> 9 feet across and five feet deep (certainly large enough to be very
> floppy), and I never used anything except wire to hold it together.  I
> did, however, use horizontal bends at all the corners of my perimeter
> runs (also for the vertical pieces at the corners).   A twenty foot long
> stick of rebar bent in the middle gave me two sides plus one foot at
> each end to overlap with the opposing two sides ... thus a total of 24
> inches of bent overlap at those corners as well.  I weigh 180 pounds and
> crawled throughout the cage repeatedly with virtually zero flex or
> shift, and there was no displacement at all when the concrete was dumped
> into the hole directly from the truck.  It could be a much different
> story if the corers were merely crossed and tied.  A section of bent
> rebar is a bracket ... a crossed and tied joint is a hinge.
>
> 73,
> Dave   AB7E
>
>
>
>
> On 1/3/2014 7:55 PM, Patrick Greenlee wrote:
>> When welding the ends of pieces of rebar as an alternative to a 
>> slight overlap and wire tying it just doesn't matter what the alloy 
>> is if you can stick it together good enough to not fall apart when 
>> pouring the concrete you have met the requirement.  This is not a big 
>> deal structural issue. Crazy glue (alpha cyanoacrylate anaerobic 
>> adhesive) would be fine if it would hold during the pour. Also kite 
>> string, dental floss etc.
>>
>> Patrick NJ5G
>>
>>
>> -----Original Message----- From: David Gilbert
>> Sent: Friday, January 03, 2014 6:34 PM
>> To: towertalk at contesting.com
>> Subject: Re: [TowerTalk] Tack welding rebar, need howto
>>
>>
>> Well, my point with the cheap stuff is that you don't really know what
>> you're welding to.  It might be part cast iron from an old engine block
>> for all I know, and that doesn't weld well at all.  You wouldn't
>> necessarily be able to tell if you had a good joint or not.   I used a
>> LOT of 60,000 PSI rebar when I built my house (ICF walls and 4,500 sq ft
>> of slab) and I was surprised how much variation there was in brittleness
>> when I bent it even for the supposedly good stuff.
>>
>> But no, I'm not really hung up on the strength of the steel itself. All
>> of it is stronger in tension than the concrete is, and if I'm in doubt I
>> just use more of it.   ;)  I only mentioned it because I thought I saw
>> someone earlier in the thread question whether a welded cage was needed
>> for strength.
>>
>> 73,
>> Dave   AB7E
>>
>>
>>
>>
>> On 1/3/2014 3:13 PM, Jim Lux wrote:
>>> On 1/3/14 12:05 PM, David Gilbert wrote:
>>>>
>>>> By the way, while I totally understand why you'd want to tack weld the
>>>> bolts to the rebar, I've never thought much of welded rebar cages in
>>>> general.  True weldable rebar (the stuff that is supposed to hold it's
>>>> strength after welding) is expensive and harder to get.  The 40,000 
>>>> PSI
>>>> stuff you can get at Lowes and Home Depot comes from indeterminate
>>>> source material (a mixture of washing machine chassis, old bed 
>>>> springs,
>>>> car frames, salvaged rebar, etc) and almost certainly will not weld 
>>>> with
>>>> consistent strength, although you can buy better 60,000 PSI stuff from
>>>> construction supply places.
>>>>
>>>
>>> Yeah, but if you're using rebar from who knows what kind of metal, are
>>> you really concerned about whether it retains the strength when you
>>> weld it?
>>>
>>> As I recall, about as weak as steel gets is 30-40 ksi.. Unless your
>>> welding physically damages the steel, I don't know how much lower you
>>> can go.
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