grade 60 stirrups experience

[mattdukes]

In field experience, do you find grade 60 stirrups more brittle? Is this recommended to use for ties and stirrups?

 

[BAretired]

In my locale, reinforcement suppliers no longer supply grade 40 bars, so grade 60 has been in use for ties and stirrups for several years. CSA specifications indicate the bending radius they must meet. Re-bending could be a problem, however.

BA

 

[asixth]

In my locale we have been using 500MPa (approx 75ksi) for about 10 or so years. Most mill certificates come in around 550-570MPa. I have never had a shear problem in the field and I hope that I never do so. Where shear reinforcement is required from the analysis I would recommend using it.

 

[mattdukes]

I heard there are different bending requirements for grade 40 and grade 60 stirrups in actual implementation in constructions. My experience is mostly on grade 40 stirrups although I mixed it with grade 60 longitudinal bars. I have never used grade 60 stirrups. What changes in actual implementation would I have to expect (in bending it for example.. is it harder and more brittle to bend)?

 

[dik]

The metalurgy has improved over the decades... about 40 years back I dropped a #3 stirrup one winer, and it 'broke'. It was common back then to spec grade 40 for stirrups.

 

[JAE]

dik is correct - I believe it was perhaps in the late 1980's that they adjusted the 60 grade rebar to work better with smaller stirrup bends and avoided some brittle cracking when producing stirrups. It was common for us to specify 60 grade longitudinal bars and 40 grade stirrups for #3 and #4 sizes.

 

[dik]

mattdukes... if you need tighter bending radii, then spec 400W (60W) for weldable rebar... it has a slightly smaller radius...

Dik

 

[TXStructural]

While there is still a good deal of grade 40 produced in some regions of the US, suppliers in many places only stock grade 60 and higher. There is no engineering reason to specify grade 40, unless you need an intentionally weak beam that holds cracks tight until yield (pre-yield crack width is dependent on area of steel crossing the crack, not the yield strength of the steel.) The actual difference in ductility between grades of A615 bar is negligible, and if unusually high ductility is a principle requirement, specify A706 (of any grade). There is little to no price premium on strength in most markets for ASTM A615 and A706 spec bars. Or switch to stainless bars meeting ASTM A955, which carries 20% minimum ductility.

Do not specify bends tighter than ACI/CRSI stirrup minimums under any case. Bars cannot be reliably bent to tighter radii and still perform properly. Also, for standard hooks, the limiting factor for bend radius is often not bar ductility but concrete performance inside the bend.

Interestingly, in-ground pool crews and other people who hand form bars really prefer grade 40 so they can easily bend them. DO NOT use that excuse for structural uses, since all structural bars should be fabricated in a shop (either at a plant or using on-site equipment, not hand benders.) The level of quality control needed to assure a safe, constructible structure demands observance of proper bends and tolerances.

As for cold brittleness, it happens with all carbon steels to one degree or another. It is seldom a factor in a completed structure.

 

[dik]

TX... does the CRSI provide for slightly smaller radii for weldable rebar? I agree with not using smaller radii; there's little to be gained. I sometimes need to do 'odd' things and it would be good to know.

Dik

 

[mattdukes]

What could be the hidden harm of combining grade 60 longitudinal (6mm) bars and grade 40 (3mm) stirrups? Is it recommended all have the same grade 40 or grade 60? We ran out of stock of grade 60 stirrups and plan to use grade 40 stirrups in combination grade 60 main bars beams. Any subtle disadvantage I may not be aware of?

 

[BAretired]

It was common practice to use Grade 60 for longitudinal steel and Grade 40 for stirrups. There is nothing wrong with that. The only problem I can think of is to design stirrups on the basis of Grade 60, then use Grade 40 without modifying stirrup spacing as required.

BA

 

[mattdukes]

We will of course adjust the spacing to accomodate grade 40 stirrups instead of grade 60. I assume there is similarly no hidden problem in using column grade 40 ties with grade 60 main column bars assuming the spacing is recalculated. Correct?

 

[BAretired]

In the case of column ties, you need not recalculate spacing. Column ties must prevent premature buckling of column vertical steel at stresses below yield point. They do not require a high yield stress in order to accomplish that.

Conversely, beam stirrups carry diagonal tension, so stirrup spacing is related to the tensile strength of each stirrup.

BA

 

[mattdukes]

Problem with grade 60 ties is if the corner bends are brittle and the crews install it without double checking.. so there is advantage in using grade 40 instead of grade 60 column ties... Has anyone here actually make it a point to choose grade 40 instead of grade 60 column ties since the yeild strength is not important?

 

[hokie66]

Must not be much of a beam if the longitudinal bars are 6 mm. Sounds like you may be worrying about an irrelevant issue.

 

[mattdukes]

sorry.. typo... i mean 20mm bar which is 6" approximately...

 

[hokie66]

20 mm is not approximately 6". I suspect you mean #6 and #3 bars. Since you are talking about Grade 60 and Grade 40 bars, it would be best to stick with the units which correspond.

 

[mattdukes]

lol.. another typo. I mean #6, not 6".. it's just that I often use millimeter like 20mm and never use #6 in bars

 

[BAretired]

Has anyone here actually make it a point to choose grade 40 instead of grade 60 column ties since the yeild strength is not important?

I did that for a long time, then found that Grade 60 was being supplied in lieu of Grade 40, the supplier believing that he had provided a better product than the one specified. I am not sure how long that condition prevailed, but I don't believe it is a concern now.

BA