AS3600 - Cogs & Hooks

[sdz]

I understand code provisions for standard cogs on end of reinf bars. What about if you have a non standard cog with the tail either greater or less than a standard cog? Can you adjust the anchorage provided in some way to allow for this? Especially, if you have a tail equal to the development length can you count it as full anchorage or are you still restricted to the cog providing 1/2 of the required developmentlength?

Same for hooks.

 

[dbuzz]

I think you are limited to the hook/cog providing 50% of the anchorage.

13.1.2.4 Development length of a bar with a standard hook
Where a bar ends in a standard hook complying with Clause 13.1.2.5, the tensile development length of that end of the bar, measured from the outside of the hook, shall be taken as 0.5L_sy.t or 0.5L_st as applicable.

I would be cautious about having a hook/cog length less than the standard lengths nominated in AS 3600.

C13.1.2.6 Standard hooks
Standard 180° and 135° hooks, and 90° cogs require the steel lengths given in Table C13.1.2.6. They are the minimum lengths which physically can be bent on a bending machine; lengths shorter than these should be specified with caution as they would not provide the necessary anchorage assumed in Clause 13.1.2.5, and illustrated in Figure C13.1.2.6.

 

[apsix]

I would also be cautious;

I wouldn't use greater than 50% of capacity unless you have calculated that concrete crushing and/or splitting will not occur.

If the length is less than standard I would use that length as if it was straight bar.

 

[hokie66]

Apsix is exactly right. Use entire embedded length as if were straight.

 

[dbuzz]

I agree with Aspix and hokie66. Hooks/cogs provide effective anchorage because they make use of bearing pressure inside the bend. Anything less than the minimum length required by AS 3600 won't develop the bearing pressure at the bend so it can be considered as simply a straight bar.

 

[sdz]

Can a short cog be counted as a straight bar? AS 3600 says 10 bar diameter radius is required to develop length around a bend.

 

[dbuzz]

sdz

You may be correct, I haven't had cause to use that clause before.

13.1.2.3 Development length around a curve
Tensile stress may be considered to be developed around a curve if the internal diameter of the curve is 10d_b or greater.

 

[apsix]

From the commentary; 10d is a limit on curvature above which the curved length behaves like a straight bar.

I understand this as meaning that you aren't limited by the 50% rule, the entire development length can be within the curve and beyond.