Rebar Welding 1

[ron8655]

In relation to the welding of Rebar to a column to provide anchorage for an RC wall. Does welding reduce the strength of the Rebar itself by making it brittle. If so is there information on this in the British standards or Eurocodes or other documents. Thanking you in advance

 

[metengr]

Welding can weaken the rebar locally at the weld joint if welding is not performed properly or the rebar material is of such a grade of steel that it exhibits poor weldability.

 

[ron8655]

Going on the idea that the rebar will be only as strong as its weakest link. Im using fy = 460N/mm2 steel reinforcement. Will welding reduce this rebars strength and if so do you have any documentation or standards i could reference to prove this in my design. thanks.

 

[metengr]

ron8655;
I can't provide you any further help because you don't have enough detail about the rebar chemical composition, weld joint detail or the material you are joining to the rebar (another rebar or steel plate). A way around this is to obtain a sample of the rebar, do a full penetration weld, and have a mechanical test lab run a tensile test on the welded rebar. This would provide you with the necessary information for this application.

 

[ron8655]

Thanks for your help. It is only a rough guide i need for my design. I will tell you my problem. I need to provide anchorage for a RC wall by connecting the Rebar in the wall to a universal column (254x254UC89) 275N/mm2 on sides, universal beam (457x191UB82) 275N/mm2 on top. The base of wall is anchored to the foundations so no welding neccesary. Welded shear studs will not provide the neccessary anchorage as wall is designed to take a blast load (10kN/m2). My choice is either drilling through the columns and beam to tie off rebar or by welding either U-bars or L-bars to the columns and beam flanges. I just need to know whether the welding will weaken the rebar (460n/mm2) to the point that it will fail under loads. Assuming a perfect 8mm fillet weld. thanks again

 

[henri2]

The reinforcing steel welding code should have provisions for welding reinforcing steel to structural steel. In addition, the code should have preferred joints which may likely have to be qualified by testing in order to obtaing a PQR and develop a WPS (recipe for weldment).

You may also have to also have a look at the structural welding code for steel as well....allowable stresses, preheat, electrode selection etc.

What is the UK welding code for reinforcing steel...is it BS 7123...or is it a BS EN designated one?

Are the MPa values yield or tensile strength requirements? I suspect yield...no?

I am sure if you review the relevant UK welding codes, it will permit welding 460 MPa reinforcing steel to 275 MPa steel, if base metals are in compliance with codes and WPS is based on qualified PQR or tests of trial joints.

Whether your proposed joint will function in accordance with the model you have envisaged, is another matter.

 

[UcfSE]

You need to specify a weldable rebar material. In the US, typical rebar is specified as ASTM A615, which is not weldable. When you need to weld the rebar, you spcify ASTM A706 material. If you are not in the US or do not use US designations, you will need to find your equivalent for your area.

I would not specify welding rebar unless the material is weldable. That's creating a potential problem that you should know better than to do.

 

[oldrunner]

The problem with standard rebar, if I remember correctly, is that there is to much sulphur. So when it's welded, it becomes brittle. Once was reprimanded for using welded rebar as temporary cross bracing. I've always been suspicious of any welded rebar because it's so easy to get mixed up in the field between weldable bar and non-weldable bar.

It might be better to maybe thread the end of the bars and pass the bar through a cut hole in the flanges.

 

[dik]

Nelson makes deformed bar 'studs' for welding to steel.

Dik

 

[ron8655]

Thank you all for your help, to answer a few of your questions:
Yes, that is the yield strength.
BS 7123 is the code alright for welding rebar for quality of weld etc, BS4449 states the rebar to be used.
However the last thing I will need to find out or maybe you would know, when the rebar has been welded is there a reduction factor for loss in yield strength due to the heat etc. Im not looking for reams of mathematical formulae just maybe a simple reduction factor for a typical weld for calculation of steel needed. Maybe this is not available but thought id ask anyway. Thanks again

 

[metengr]

How about this;
if you weld the rebar and cannot achieve a full penetration weld, assume a 0.74 reduction factor in tension. For shear load, assume a 0.50 reduction factor.

 

[deanc]

Coat hangers work good for gas welding....kidding.

If there are welding problems,as listed above,use this old trick. Attach a piece of known good material to the rebar(preheat,E6010,wire weld,PWHT,etc.)may need to do some bends or testing. Then make your attachment from it.

 

[ron8655]

Yea that would be an option, except it will require a lot of onsite fabrication and welding which is not desirable.
metengr: those factors seem reasonable but could i just ask where they came from? thanks

 

[metengr]

They are from my Codes/Standards days.

 

[henri2]

ron8655: Does BS 7123 have a table for allowable stresses...stress reduction factors...?

metengr: I have a question on terminlogy for you. In D1.1-00 Table 2.3, which is similar, to D1.4-98 Table 2.1, allowable shear stress on fillet weld effective area, is given as 0.30 x nominal strength of filler metal. What is the proper term for the factor 0.30?

 

[metengr]

henri2;
I would call this a shear strength reduction factor. The shear strength is typically 0.60 x the UTS, whereas, the shear yield strength is 0.58 x the tensile yield strength.
The 0.3 is obviously an additional conservatism.

 

[ron8655]

RE: ron8655: Does BS 7123 have a table for allowable stresses...stress reduction factors...?

No, unfortunately it doesn't. Only states that rebar of 500N/mm2 yield stress should be used. thats fine but I have to validate the strength of the connection against various forces, and to say the yield stress is still 500N/mm2 after welding is not correct.
I have been given reduction factors by metengr, thanks, but will have to find the exact code or standard they are from (British Standards). The reason for this is that when my design is auditted I have solid evidence of where the various numbers came from.