development and lap length of rebar - is db nominal or actual diameter

[ajk1]

In CSA A23.3 - 2014, Design of concrete structures, the formula for compression deveopment and lap length of rebar is given in terms of d_b. In the definition of symbols at the front of the Standard, it says d_b = diameter of bar. It does not say whether it is the nominal diameter or the actual diameter. For some bars, such as a 10M, there is a significant difference (10 mm vs. 11.3 mm, etc.). The table for compression development length in the latest CAC Handbook seems to be based on nominal diameters. In the same table in an older edition of the Handbook it seems to be based on actual diameter
Does anyone know where d_b is stated to be the nominal diameter?

 

[ajk1]

To rapt: No. Let me explain, although if you are Australia based, I suspect you already know this:

A soft conversion as defined on this continent is when the imperial dimension of a product is simply converted to a metric dimension, but the product itself is not changed. An example of a soft conversion is an American imperial #4 rebar, which has a 4/8" or 1/2" diameter, of 0.20 in² area (129 mm²) of 60,000 psi yield, being referenced metrically as 12.7 mm or 13 mm rebar, but the manufactured product undergoes no change whatever. This is what the U.S. did. I believe they refer to this as a #13 bar.

In contrast, Canada did a hard conversion i.e. the production facilities were altered to produce a 10M metric bar of 100 mm² area, and of 400 MPa (58,000 psi) yield strength.

Canadian metric rebar is as follows. This is hard metric, as you can see from the areas. Imperial rebar is not generally sold in Canada. On the other hand, American metrically designated rebar is exacytly the same as the old imperially designated rebar.

10M 100 mm2
15M 200 mm2
20M 300 mm2
25M 500 mm2
30M 700 mm2
35M 1000 mm2

Imperial rebar

#3 0.10 in2 = 65 mm2
#4 0.20 in2 = 129 mm2 = #13 soft metric I believe
#5 0.31 in2 = 200 mm2
#6 0.44 in2 = 284 mm2
#7 etc.
#8
#9
#10
#11

Hope this helps.

 

[Chickenhawk6451]

Rapt: I misunderstood the initial query not knowing the hard/soft metric was at play. Thanks for the correction

ajk1: Thanks for the info, glad i don't need to deal with uncertainties like that in our supply chains

 

[rapt]

ajk1,

Any country that uses the name 10M to define an 11.3mm diameter bar has used a soft conversion!

Any designer who uses 10mm as the diameter of that bar in any calculation related to bar diameter needs to go back to school!

Just because the idiots writing the code or defining material names want them all to look "metric" being whole numbers to the nearest 5mm does not mean that designers have to be just as stupid. Logically, it should have been 12M! Most countries adopted rounding to a whole number and generally working in increments of 2 for low bar diameters and 4 for higher bar diameters, every now and then with an outlier like 25 thrown in.

Unfortunately in Australia we allowed a statistician to determine our nominal concrete strengths. So we have to put up with the illogic of 25, 32, 40, 50, 65, 80, 100. At least they called them the same name as the strength, but they certainly are not "metric". What is wrong with 30 and 35 and 60 and 70? We can use it but have to call it special grade concrete!