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View Full Version : Building a small rebar cage - weld it?



vsheetz
11-21-2010, 01:16 PM
I need to build a small rebar cage (about 2x2x3 feet) for a concrete foundation and have a Millermatic 175 MIG welder. Seems welding it would make it more solid and easier to handle.

Pros and cons of welding it together vs using rebar ties?
Perticular type of rebar needed, or can I just use the stuff from a big box home store?

Thanks in advance!

dda52
11-21-2010, 03:41 PM
For me, it would depend on whether or not it would be inspected. If it will be, then it must be tied unless specifically instructed in the plans to weld. That would be the first consideration. I have inspectors make me take sections out where electricians have welded ground lugs to the bars. They do not like the heat at all. On some jobs, we aren't allowed to even have a torch on the job much less use one.

As to rebar, weldable bar will have a W suffix on it. Most rebar is not weldable per the rules. It will weld to be sure as I have done it a million and a half times. It won't however be an approved method on anything except W suffix bar. The box stores will not have the right bar for welding. My rebar supplier wouldn't even have it..he'd have to order it. It is NOT cheap either. http://www.dot.state.il.us/materials/rebarguide.pdf Start on page 4 and ytou will see examples of the W suffix.

I say just tie it and be done with it. You can tie it much faster than welding anyway, any day.

Blacksmith
11-22-2010, 08:46 AM
Tying is the norm and is generally accepted. The rebar and the concrete kind of work together to form a finished product like fiberglass cloth and resin. Welding the rebar would be akin to sewing all the fiberglass strips together before adding the resin. I know some high performance boats have sewn cloth, but it's definitely the exception.

Sberry
11-22-2010, 09:14 AM
Depends on how critical it is, I have tacked a lot of it together for rather rudimentary work, does make it nice to handle.

old skool
12-03-2010, 05:08 PM
Main thing to remember when welding re-bar is not to cool the hot welded joints with water & you should be good to go.

usmcpop
12-03-2010, 05:33 PM
Main thing to remember when welding re-bar is not to cool the hot welded joints with water & you should be good to go.

Crap.

In case the reply is too short, I should type "Crap" and maybe the bot will take it.

Skymeat
12-04-2010, 12:13 PM
Just tie it. All you need is tie wire and pliers. If it's a decent job you should be able to climb on it.


http://static2.bigstockphoto.com/thumbs/2/2/4/large2/422552.jpg

gtcway
12-04-2010, 04:52 PM
I've been told (can't say for sure) that you shouldn't weld rebar to use in concrete.

dda52
12-04-2010, 07:12 PM
You can if its designed for it and uses the correct bar. I have done it many times. Some bars must be welded. #32 bars for instance. You overlap two 4" plus bars and you have a huge mass of steel to encase. They are usually butt welded together in columns and the like.

old skool
12-05-2010, 02:09 PM
Crap.

In case the reply is too short, I should type "Crap" and maybe the bot will take it.

??????????

usmcpop
12-05-2010, 02:58 PM
I mean that just not cooling with water and you're good to go is nonsense. You can get brittleness even without quenching if it's not a weldable grade of rebar.

dda52
12-16-2010, 09:37 PM
Typical overlap for most applications is 40 bar diameters.

Steve from Ohio
12-17-2010, 12:36 AM
I have an old Italian friend who is retired from the cement trade. He's now about 85 years old. Knows his stuff.

I asked him that very question a few years ago as I was building an earth bermed house and using concrete for a wall.

He told me that concrete does move to some degree when heated or cooled.
He mentioned that the steel reinforcement if welded would move differently than the concrete around the steel reinforcement rods which may cause spalling. He told me that welding the rods together would prevent them from moving within the concrete. He said that pre-stressed concrete cannot and should not be welded due to that very problem.

He did say that some rebar can be welded in certain instances but that rebar must be rated by the mill as weldable for it to be weldable. He mentioned that most rebar used in the USA cannot be welded. He said that tying with wire is the accepted practice for correct rebar placement.

In short, don't do it. Tie it together with wire.

SidecarFlip
12-17-2010, 09:14 AM
My sole comment is this...

Most rebar is produced from scrap steel of questionable metallurgical content, that is, rebar is very low on the quality of ingredients scale. To my knowledge, there is absolutely no rebar cast from metallurgically controlled ingredients. It's all junk.

Consequently, welding of rebar to form any shape will almost always change the grain structure to the detriment of the material, in other words, don't do it.

Wire ties are the proper and industry accepted method.

Sandy
12-17-2010, 12:56 PM
The whole affair must have more to do with multiple independent overlapping pieces of re-inforcements (wire tied) incorporated into the poor versus a more rigid, less flexible mass (welded) and how it all works together than it has anything to do with the actual strength of the connection.

I mean that wire just isn't that tuff. If the man with the degree says that wire is better than weld there's no reason to doubt that, but there just has to more to it than whether two bars tied together are stronger than two bars welded together.

Is it possible that they tie it so that it can move rather than weld it so that it can't ??

I don't have a clue as to why they tie it instead of weld it but I do know if there was that much mojo in that wire we'd be tieing more chit together (farmer style) than welding. :D

dda52
12-18-2010, 10:39 PM
Well guys, never say never. I have just now opened up my plans for a concrete deck over an old chlorine pumping pit. The engineer is spec'ing A615 G60 rebar welded to the structural steel I am placing and to itself. :eek: This is the first time in 25 years I have gotten that in writing.:rolleyes:

SidecarFlip
12-18-2010, 10:53 PM
...but we all know most engineers are book smart and actual procedure ignorant.

My BIL is a design engineer for a not to be mentioned automotive manufacturer here in Michigan and he can't change a light bulb, takes his car to the 10 minute oil change place and his tires are always underinflated......:D

Most, not all.

Maybe 99%:eek:

dda52
12-18-2010, 11:53 PM
Well, this one is a good structural engineer. Been working with him for about 8-9 years now. He knows his stuff. I'm going to ask on Monday if he meant W suffix bars. It may not matter much. This floor is all of 8'x9' and will support maybe 2000#. It isn't a huge deal....but regardless, I can guarantee you I will be welding those bars on Tuesday or Wednesday as specified. I just build what they draw.:rolleyes:

SteveK11
09-23-2011, 08:32 AM
Wonder if he ever finished that deck? :D

I'm going to Home D. tomorrow and pick up some rebar. I'm looking to weld up a frame for a tarp to cover a car... so I don't get soaked (going to rain) this weekend working under the car (in the driveway). :eek:

Hope it welds good enough to support the tarp. :confused:

Sberry
10-10-2011, 10:17 AM
Tying is fast and doesn't add stress risers to the rods, unless this is engineered deal it doesn't mean squat, have welded hundreds of pieces of re bar over the years for all kinds of things, not really much of an issue. A rod with 40 diams splice length ain't gonna move any more than a welded one. The ties do nothing for the actual strength, they simply hold the rod during the pour. Lots of rods are not even tied, simply "floated or shoved into the pour.

fbcwelder
10-10-2011, 08:08 PM
SidecarFlip said it best...and a couple others, rebar is junk metal, i deal with it a lot where im at and they always want to weld it...sometimes it holds other times its like cast...tie it...

Sberry
10-11-2011, 09:21 AM
How would they ever be able to engineer it if it was junk and was as brittle and uncontrollable as cast? I can't ever recall a case where I welded a piece for some common home brew stuff that failed, its kind of a habit to grab a 7018 for it,,, one can kind of tell how hard it is by bending which would be another no no if it was brittle. Common footer and that type of work usually isn't so closely engineered that all this makes much difference, biggest factor is rod size, count,, and placement. Highly engineered silo;s, slabs and other structures the QC is a different factor but a common pier in a home brew deal just isn't that sophisticated. Rods get welded to embedded steel all the time.

fbcwelder
10-11-2011, 06:49 PM
well sberry not all bar is the same... go buy some low dollar stuff like most places are doing now and let me know...you mean to tell me its all quality steel??? thats a first...you will find out that a lot has flaws...im not talking about building a freeway im talking about a little pour...get back with me

Sberry
10-11-2011, 07:07 PM
What would it matter for a little pour? If it does its designed wrong or shouldn't be done by an amateur then.
Quality has gone up on almost everything,, or if it hasn't the price has gone down. Well proven by Chinese tools in the last couple decades. I would certainly be willing to see some actual evidence of fundamentally flawed steel. We could start a new thread for it, lets see how many pieces of crappy rod we can find.

fbcwelder
10-11-2011, 07:41 PM
its not that its a small job, its what you said about the quality of the bar...you really think corners are not cut...haha i work for the gov. , so start a thread because i cant cover it in one night... im not saying your totally wrong, but your not right

wmgeorge
10-12-2011, 04:15 PM
I wonder how much of the Rebar comes from India and China? A lot of the steel pipe used for gas, water you name it does. It is C**p, I hated to see it on the job. Surely there is testing and classification for Rebar used for important projects.

Sberry
10-12-2011, 05:39 PM
I would hope so. I wasn't implying that there isn't junk out there but didn't want to leave the impression that every time a guy struck an arc on a rebar he was headed for tragic failure. Like the man said,,, will it hold a tarp? Probably not a project that involves hi QC, same with most common footer steel unless involved in highly engineered projects. Even bigger errors occur in size and placement, rod quality is probably pretty low on the list and just tend to believe that welding it and it turning out like cast is kind of,,, likely exaggerated to some extent. Not saying it couldn't happen, hit a bad spot or something, have had some frac from improper bending that was USA even,,, but I never had it happen, wouldn't consider it a likely outcome.
This isn't taking a shot at anyone in and is just an opinion from experience.

Krunch
10-13-2011, 09:42 AM
I've heard rebar is like A36 in the sense that "We don't know WHAT'S in it." They don't spec it, because they don't test it because they don't care.

Might be mild steel, might be hi-carbon steel. Whatever was in the crucible at the time.

And I suspect that's where problems can surface if you weld it. For example, if you weld high-carbon steel with the wrong filler or without the right heat treatment, it can crack ... so they say to wire tie it to be safe (unless it's rebar rated to be welded, in which case I suspect they spec/test it)...

That's my theory, anyway.

Mandy
10-14-2011, 01:37 PM
Would if be OK to weld the rebar cage together for my TX-455 crank up tower base, rather than using tie wire? Seems it would be better, but I thought I read of some problems with welding rebar.

Sandy
10-14-2011, 02:35 PM
There just can't be any significant strength in that cheezy soft wire that you tie rebar together with, all it can possibly do is hold the rebar in place untill the concrete gets poured. So in that context I don't see how there could be any difference between a couple of wraps of wire and couple of decent tacks. It's the combination of the concrete plus the concrete surrounding the rebar that makes the structure not a piece of wire or a tack.

In the cases where the rebar is required to be welded it will be just that, welded and not tacked, and welded under a spec and probably wedable rebar so tieing isn't an option or a discussion point. Design engineer says do it my way or go home.

As far as building a structure of your own, such as a cage, you have to make some intelligent decisions of your own such as "how much does it matter?". You've got to be using rebar either because that's what you've got in hand or you're cheap and strength is a minor issue. In that case weld it up and see what happens. Or heck, wire it together if that wire does such wonders.

ptsideshow
10-14-2011, 03:30 PM
There is two basic kinds of rebar the stuff that is sold at local brick/block and cement joints and Home Despots and Highes! Then there is the spec stuff that is used for building large buildings and roads and bridges that is supposed to meet standards.

A couple of years ago, modern marvels or a show like that had one on steel they showed a couple outside of LA that was making rebar from a mix of old Railroad rails and assorted steel scrap they mentioned what percentages were used but it wasn't important at the time. They did say that it wasn't used for the larger multi story type projects.

Not the same type of cage but may be of interest.

I remember about 15 years ago seeing some travel cages for some lions and tigers that were made of angle iron with wood floor and tops with the sides being ½"or ¾"dia rebar with a strap steel piece half way up lengthwise on the rebar. The cages sides were about 42"to 48" tall.

I have used rebar as both the frames for the grates to hold the meat in the smoker, and thee fire grate in the firebox
http://i35.photobucket.com/albums/d200/ptsideshow/Bobs%20Smoker/DSCF0013.jpg
fire grate Flux core

LarryO
10-14-2011, 04:00 PM
In OZ there is only one spec for rebar unless its gal coated or SS.
I think i have some SS rebar somewhere. Would be expensive.


Most is tied on site here too, with the exception of pile footing cages that are wraped in a spiral on vettical rebar. Never seen one of those tied, only welded.

cranky
10-14-2011, 04:41 PM
This thread is a year old !

Stick-man
10-18-2011, 08:41 AM
I actually weld rebar for my customer who then sells it to the steel mills. They're called chicken ladders. The mill uses them to hold the refractory to plug the bottom hole in the kettles. I'm even doing a batch today. If you're going to weld it, use 7018. I've tried ER70S-6, Hobart Fabshield 21B E71T-11, 6013 and 6010. I've only had acceptable results with 7018. I will try to get some pics and post them here.

Sberry
10-19-2011, 09:19 AM
Yes, a lot of that kind of stuff is built from re-bar every day. Thats kind of why I flinch when something comes up that says rebar cant be welded. Heck even cast is often welded with a mig, lot of times it works just fine too. Not ideal and you might have tough time finding engineer to stamp it.
We welded the rods in my storage building foundation, made it solid and had bolts located even before forms were put on, the whole thing was bigger and heavier than it needed anyway, all low stress, made it easy. electrically bonded the whole building,, ha. Done a lot of it without tying too, just go along and muck the rods in, dowels, do laterals tossed in right long with the pour.

Northweldor
10-23-2011, 08:50 AM
Got interested in this and did some reading, and it seems the welding prohibition on critical engineered applications is due mainly to the fact that results cannot be predicted due to the poor quality control on the parent metal, and the fact that welding also can cause unpredictable changes in yield strength which can cause failure in highly stressed applications. So, for static loads, the main concern would be that welding transfers expansion and contraction forces (approximately the same for rebar and concrete) in unpredictable ways that could cause spalling and failure.

Dmaxer1
10-27-2011, 10:21 PM
I need to build a small rebar cage (about 2x2x3 feet) for a concrete foundation and have a Millermatic 175 MIG welder. Seems welding it would make it more solid and easier to handle.

Pros and cons of welding it together vs using rebar ties?
Perticular type of rebar needed, or can I just use the stuff from a big box home store?

Thanks in advance!

It's a good thing vsheetz thanked you (for all 35 replies) in advance, as it appears we haven't heard from him since his initial question:rolleyes:.

Northweldor
10-28-2011, 07:01 AM
It's a good thing vsheetz thanked you (for all 35 replies) in advance, as it appears we haven't heard from him since his initial question:rolleyes:.

What matters to me (and most posters here) is the accuracy of the information posted. The thanks, while welcome, and the age of the post, are largely irrelevant, and we all know the cage has been built long ago! There are always those with a mission to read the dates for us, though.:rolleyes: