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Home > Forums > Engineering Forums by Industry > Constructed Items > Transmission structure engineering Forum

Actual size of #18J rebar

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JWKilgore73 (Structural)

22 Feb 12 12:57

I've specified #18J rebar many times for tubular-steel pole anchor bolts. I know they are #18 "Jumbo" bars, and as I understand it they are rolled from a slightly larger stock bar. The deformations at the end are then turned down/shaved off back to 2.25" diameter, and the threads are rolled into this smooth area to fit a standard 2.25" UNC nut. If you don't start with a larger bar, you cannot fully develop standard 2.25" UNC threads because of the deformations.

My question is, what is the diameter/area of the "slightly larger" bar? I can't find any standard specifications. Is an 18J a standard size or does it vary by manufacturer?

Thanks,

JWKilgore73 (Structural)

23 Feb 12 19:16

I got the answer from a different source, so I'm following up here:

Quote:
The 18J has a weight of 14.60 lbs. per foot compared to the 13.60 lbs. / foot of a standard 18 bar. The minimum body diameter is 2.214" on the 18J with rib heights of 0.102" minimum. The area of the raw bar is 4.29 square inches vs. 4.00 on the 18. The increase in diameter allows for the milling/threading operation and produces a "bolt" with a tensile stress area of 3.25 square inches which is the same as a 2.25" bolt. The threads are slightly modified from standard 4.5UNC, but ASTM A-563 Grade C nuts (tapped oversize for galvanizing) fit. It is important to roll the threads rather than to cut them otherwise the bolt capacity is decreased. The bolt material complies with ASTM A-615 Grade 75 (100 ksi tensile) with some additional requirements that are not listed in A-615, such as Charpy impact values of 15 ft-lbs at -20 degrees F.

I won't mention the source, (he may not want his name out here), but he's reliable.

transmissiontowers (Structural)

23 Feb 12 23:38

We have gone away from rebar bolts to smooth bar F1554 or A193-B7 for out large bolts. We are not in a seismic area, so we don't worry about a ductile failure. Our smooth bolts go up to 3" diameter at 105 ksi.

If you are in the business and do substation structure design, you might look at ASCE 113 if you haven't already. It is due for an update and we are looking for new members.

_____________________________________
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