Mixing A706 and A615 Rebar 1

[tolchijb]

Is it standard practice in high seismic regions to specify A706 rebar only or do you only specify A706 at ductile elements and use A615 everywhere else. If you do mix rebar, how is it delineated as different in the field other than standard bar markings that are not going to scream that this rebar is different?

thread507-226454

 

[TXStructural]

There is no need to mix. The price difference, if you can actually get A615, is inconsequential. Much of the bar in the western states is dual-spec (A615/A706), so you will likely get higher ductility without specifying it.

We do not encourage use of A706 elsewhere because of the limited availability of certain metals, such as vanadium, used in chemical grain refinement (the usual means of achieving greater ductility in rebar and structural steel.)

The other aspect of A706 which is important to seismic application is a cap on the upper bound of yield strength. Right now, A706 limits the strength to 18 ksi over the nominal value.

 

[tolchijb]

The project I am working on is in South Carolina so I am not sure if dual grade is the norm there. I guess I should make a call and ask the question.

I want to verify to make sure I understand your post. You would specify A615 with the specific requirements (actual yield no more than 18,000 psi above specified fy, and ratio of actual tensile strength to actual yield strength not less than 1.25) vs. specifying A706. You would do this for all bar, not just at ductile elements. Is this correct?

 

[TXStructural]

No, specify A706 for the project if the material is available (I have a call in to find out for you.) If the contractor needs to sub A615, then you can agree if the material meets the requirements you mention. The hard part is that they would have to know every heat of steel provided for the ductile members meets the requirements.

 

[TXStructural]

A706 is produced in limited quantities in South Carolina. The fabricators may also stock materials from other mills, but I would recommend specifying only those bars in elements that require A706 ductility be shown on drawings using a (D), with an appropriate plan note or general note indicating the (D) designates the use of A706 bar in the appropriate grade.

The supplier or contractor can then request a variance to use A615 with the appropriate properties, in lieu of A706.

 

[slickdeals]

I would be wary of specifying the same bar size in A615 and A706, regardless of how bulletproof your drawings and notes are. Remember, if there a 50-50 chance that a contractor can screw it up, it's likely to happen 9 times out of 10. If the element is cast with the wrong grade of steel, you have no choice but to tear it down.

 

[TDIengineer]

On a project I did, we did not specify A706 for jamb bars in a masonry wall as I usually only do this in concrete shear walls per the ACI code section. However, the state field engineer insisted. There was a change order cost by the contractor to go with A706 over A615 in California. it wasn't huge, but there was a cost difference.