AS1554.3 Welding of Reinforcing Steel

[OzEng80]

I understand that welding of reinforcing is to be avoided but looking through AS1554 there doesn’t seem to be anything overly prohibitive there?

Am I correct in saying that if class N reinforcing is welded in accordance with Table 3.2 (ie W50X) no reduction in strength is required? Or are some intensive testing proceedures required?

I have only used welded reinforcing for cast-in-plates, tags etc..and adopted a 250 MPa yield stress for class N reo that has been hit with a weld, due to inhouse direction. Is this too conservative?

Thanks!

 

[hokie66]

AS3600 says that "Welding if required shall comply with AS1554.3. Tack welding not complying with that Standard shall not be used". In my opinion, the key word is "required". Welding of reinforcing steel is not required just to hold it in place.

I don't think your inhouse direction is too conservative.

 

[OzEng80]

Thanks hokie

I am still confused by the fact that AS1554.3 has no statement about using a reduced yield stress for affected reinforcing. This leads me to believe that if the correct welding equipment is specified no reduction in fy is required. I have also read elsewhere in this forum about the American code permitting welding for specific reinforcing grades and equipment - but i don't know how this correlates to true blue steel.

If a reduction of fy is required for welded reinforcing can you direct me to any reference material that has the design requirements?

 

[hokie66]

I think the point is that if the welding of reinforcing steel is done correctly, the full strength can be developed. But the execution is the problem. Welders who weld structural steel need to use different techniques on reinforcing steel. Many engineers, including myself, just don't trust welding of rebars on site without very conservative assumptions as to strength.

Other than poor welding practice, the other problem is embrittlement of large bars where small crossing bars are tack welded.

 

[OzEng80]

Agreed that site conditions/skill is inadequate but what about shop fabricated reinforcing - cast in plates etc.. with N grade tags? Is it necessary to reduce fy to 250MPa in these scenarios or just for site welding?

 

[apsix]

As hokie said, if done properly there is no need to reduce fy.
If welding to a plate you will be limited by the plate strength which will be 350 MPa at best.

 

[OzEng80]

So is 'properly' merely defined by the welding material as per AS1554 or is a more rigid specification required (again just for shop fabricated components)?

Thanks.

 

[sdz]

500PLUS® Rebar Welding Guide

This document provides information on welding of 500PLUS Rebar. Procedure for specific weld types with advice on electrode types, weld length etc. is also included.

http://www.onesteel.com/productspecs.asp?specID=2863

 

[hokie66]

In following the Guide referenced by sdz, be careful that your steel is actually Tempcore steel. A lot of the imported stuff is not as readily weldable.

 

[OzEng80]

Thanks sdz

Have you seen a similar document for standard N grade reinforcing?

 

[hokie66]

That is the standard N grade reinforcing produced in Australia.

 

[OzEng80]

Excellent. Thanks for your responses!

 

[OzEng80]

I think this is still appropriate to this post...

Further to welding of N grade reinforcing bar, I was after clarification of allowable field bending and heating of reinforcing and subsequent reductions of capacities.

http://www.eng-tips.com/viewthread.cfm?qid=207584

has links to document that in summary states that:

Bars up to N16 can be cold bent (once) without reduction in yield strength (N16 have 5% reduction)

Bars above N16 can be bent once heated (within specified heat range) with a reduction of only 10% of yield capacity.

I was pretty surprised by the relatively minor reduction in capacities given the taboo mindset of heating reinforcing on site.

So:

Are these figures appropriate for N grade reinforcing?
What is the significance of the elongation reduction? Loss of ductility?
How can the specified heat ranges be enforced/monitored?
Is there a ‘heating of reinforcing for dummies’ document that could be given to a builder?
What would be appropriate capacity reductions for a bar that has been hot bent without not in accordance with these specifications (just a big mug with a gas torch)?

I understand that heating reinforcing should be avoided but I still wish to understand this for:

Assessment of the capacity of reinforcing that has already been heated and bent.
Guidelines that can be provided to site for critical applications (for heating and bending).

Many thanks!

 

[apsix]

AS3600 Cl 19.2.3.1 is fairly clear on bending limitations.
Basically;
- cold bend around min. dia. pin as specified in code
- hot bend, OK if < 450 deg, reducing to 250 MPa yield if temp is > 450 deg & less than max. of 600 deg.
- Do not bend in same location more than twice.

Further info can be found here;

http://www.onesteel.com/images/db_images/productspecs/Applications_Advice.pdf

 

[sdz]

Be careful of hot bending! My experience is that the bars might be heated at one point almost to melting point so the end up with a right angle bend instead of a radiused bend.