Threading rebar - what is rod diameter between ribs? 1

[structuresguy]

So I have a project where we need to thread some rebar, to create an M20 metric thread on a US standard size bar. I am wondering if we need to spec out that they start with #7 or #8 bars. I dont know what the max shaft diameter will be, after the ribs are removed. I am leaning to the #8 bars, since that should be more than plenty.

Anyone have any idea on this?

Thanks

 

[Ron]

The deformations are not considered in the bar diameter, so the net diameter is the bar size. A number 8 is 1-inch in diameter.

 

[msquared48]

The AISC Steel Design handbook has net atea for different bar diameters that should be close enough...

Mike McCann, PE, SE (WA)

 

[hokie66]

I think a #8 is what you want. Look at page 39 of the attachment, which is for Australian metric bars. It says for 20 mm threads, you need a 24 mm bar. The reference also gives the tensile capacity of the threaded part of the bar. The tensile strength is reduced from the full capacity of the bar because of the reduced area, and also because the centre of the bar is not as strong as the outside.

http://www.adcommission.gov.au/case...nt-A-2.9.2-OneSteel Manufacturing Pty Ltd.pdf

 

[CANPRO]

Hookie66 is correct. I went down this road recently. If you want to create a particular size thread on a peice of rebar, you need to spec rebar slightly larger than your thread size. I didn't realize this and got to have a pleasant conversation with the contractor afterwards.

 

[BUGGAR]

Threaded rebar for anchor bolts is common in the U.S. utility industry. I suggest something there.

 

[structuresguy]

Thanks for all your help. We had spec'd a prefab product (Peikko HPM bolt), based on the equipment manufacturer's recommendations. But now we find that the US distributor no longer carries that product. So we are working to find something similar, and the closest thing i can find is a threaded Grade 75 rebar. of course, this is all last second, and holding up the GC now. But he also had the drawings for a long time before he tried to source the anchors. So lack of planning.... (you know the rest of the saying)

 

[sticksandtriangles]

If you are still having trouble finding threaded bars, you might want to look through a company called Dywidag. They make a threaded bar product I used once to bypass development length requirements for a pilecap. Might be a product you could use.

Link

 

[azcats]

This is a little primer on rebar threading from Portland Bolt.

http://www.portlandbolt.com/technical/faqs/rebar-threading-issues-and-solutions/

I looked into all this a couple years back when we were trying to attach something threaded to an existing Lenton rebar coupler. Rebar was our first thought. But it wasn't large enough diameter after it was turned down to put threads on it. We ended up using some F1554 stock with standard threads on one end and had it taper threaded to match the rebar coupler on the other end. Had to involve separate shops though because not a lot of people had the Lenton threader.

 

[structuresguy]

Good article from Portland. Thanks. We actually reached out to them to see if they could provide the anchors, and they told us they do not do any metric bolts. I was pretty surprised, and very dissappointed by this. They are sort of what I consider the leader in the bolting industry, but lack of metric is frustrating. Many of our clients are going metric, even here in the US. But Portland is not alone. For this project, we had a heck of a time convincing the GC and concrete sub (who is providing cast in anchors) that they needed to use metric. We had to keep rejecting their submittals at least 3 times becuase they werent using metric.

 

[Lomarandil]

Just curious, StructuresGuy, what is driving the change to metric for your clients and this project?

 

[structuresguy]

We are providing foundations for a variety of very large scale precision machines (milling machines, balance machines, etc). Many of our clients are European or Asian companies, and most of the specialty machines are made by European companies, and being shipped to the US. So wherever there is interface between the machine and the foundation, the manufacturer is requiring metric anchors. Also, all the dimensions of the foundation are provided to us in metric, and to avoid discrepancies as much as possible, we detail the foundations in metric (sometimes with imperial conversions).

 

[Ingenuity]

Now you just have to find a site superintendent who knows how to read a metric tape measure!