Rebar Mat Use/Availability 1

[GreatDane2022]

Anyone using welded rebar mats (not to be confused with wire mesh)? Just hearing about these for the first time and would enjoy learning more and hearing opinions.

Thanks in advance!

 

[BridgeSmith]

Not sure how that differs from deformed wire mesh. Kind of think that the larger sizes of deformed wire mesh are actually made with deformed bars. I don't think it's a coincidence that only sizes they seem to make are the ones corresponding to #4 (D20) and #5 (D31) deformed bars. It seems that they are made to order items, though, and nobody keeps those sizes in stock. We're going to start specifying mesh in those sizes for reinforcing bridge approach slabs. We'll see how it goes.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[GreatDane2022]

Thanks Rod. I believe you are correct that deformed wire mesh is what I am trying to say. I just learned of this product and the author of the article I read adamantly says not wire mesh but now see that he just meant smooth, smaller diameter mesh as specified by WRI.

I do like the idea of this product and really wanted to try on one of my small design-build walls but I am not seeing any local suppliers. As you mentioned, I suspect they’ll fab it but just don’t stock it.

So much to learn/do.

 

[BridgeSmith]

Fyi, in case you weren't aware, the designations indicate the type and size - "D" for deformed 'wire', "W" for smooth wire, the numbers with the letters indicate the area of an individual wire (in hundredths of a in^2), and the following numbers representing the respective spacing of the wires. So a "D20 x D31 4 x 8" mesh would have deformed wires that have an area of 0.20 in^2 (same as a #4 bar) at 4" spacing in one direction, and 0.31 in^2 (same as a #5 bar) deformed wires at 8" spacing in the other direction.

Also, if you haven't noticed yet, the typical supplied design yield strength of the deformed wire is 70 ksi, with higher yield strengths also covered by the ASTM spec, although I doubt you'd have any luck finding anything available in the higher strengths right now.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[Seppe]

WWR mats are commonly produced using 80 ksi material, and using wire sizes up to and including a D31.0 (deformed wire with steel area = 0.310 in2). I know of several wire producers who appear to operate comfortably in both cast-in-place and precast concrete markets where the larger diameter reinforcement is desired for structural applications. Not really that hard to find them, and they are able to manufacture intermediate wire diameters to suit.

To the original comment regarding welded rebar mats... there is actually a spec for this material: ASTM A184. ACI appears to accept these mats for limited use in structural applications. If you look at the ASTM spec you see that the welding is actually deferred to AWS D1.4. Yet, when you dig into AWS there's zero reference to the "crossing bar" joint itself. So how this joint gets welded is largely a grey area, and appears to fall in the lap of the EOR.

I've heard of select instances where rebar has been welded using electric resistance welding like is done with WWR, but I've yet to see an actual ASTM standard for machine-welded rebar.

 

[BridgeSmith]

Well, maybe it's just my area of the country (mountain west) where the WWR in larger sizes hasn't become common yet.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[dauwerda]

If you look at the ASTM spec you see that the welding is actually deferred to AWS D1.4. Yet, when you dig into AWS there's zero reference to the "crossing bar" joint itself. So how this joint gets welded is largely a grey area, and appears to fall in the lap of the EOR.

This made me curious so I took a look at the 2018 version of AWS D1.4 that I have. While the end result is essentially what you stated above, it does address it in a limited capacity:

6.2.3 Cross Welding Bars. Welding of bars that cross shall not be permitted unless authorized by the Engineer.

 

[JLNJ]

I've only seen rebar mats used once - probably close to 30 years ago - in a mat slab where the "typical" mat was used everywhere and additional bars were added where they were needed. I think the typical mat was #5s at 12 E.W. in two mats, top and bottom.

Have not seen it since.

 

[GreatDane2022]

Thank you very much everyone, this was very helpful. I was fascinated by the option for what seems to be “better, faster, stronger” (did I date myself?) but admittedly have just started thinking about this. I suspect I would see it in use more if it was “all that” but I will continue to learn.

 

[BridgeSmith]

We decided to try it out to minimize detailing effort. Calling out all the various length bars in our approach slabs is tedious, especially with skewed and/or odd shaped slabs.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[Seppe]

I do think there is some merit to using WWR for the purpose of easing "in house" detailing as you've noted. From what I've experienced, the detailing still gets done, but it's handled by the fabricator's WWR detailer in the form of a submittal that the engineer would review for design conformance. In that regard it's not too different than rebar, though I personally think WWR submittals can be easier/quicker to review given how much geometric information the detailer is obligated to show.

In the end the key is making sure the use of WWR actually makes sense. There are definitely applications that aren't a great fit for it, namely those reinforcement arrangements that have really high steel areas located in fairly small spaces. For example, you're not going to see WWR used to replace a group of five #9 flexural bars in a beam.