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AS 3600-2009 Clause

AS 3600-2009 Clause

AS 3600-2009 Clause

In clause, in the text "Where a bar ends in a standard hook complying with Clause, the tensile development length of that end of the bar, measured from the outside of the hook/cog, shall be taken as 0.5 Lsy.t or 0.5 L_st as applicable", I could not figure out what the "0.5 L_st as applicable" refers to. Since the bar ends in a standard hook/cog, shouldn't the bent portion of the bar contribute to one half of Lsy,t as pointed out by Warner et al (reinforced Concrete 3rd Edition, p.173) ?

RE: AS 3600-2009 Clause

0.5 Lsy.t and 0.5 Lst are the same concept, the length of a hook is half the straight development length. Use Lsy.t if you want the hook to develop the full yield strength (fsy) of the bar. Use Lst ( if you only need to develop a portion of the yield strength.

RE: AS 3600-2009 Clause

Thank you cooperDBM for your comment.

I wonder if this clause was written to make design easier by assuming that the straight portion (measured to the outside of the cog) contribution as 0.5L_st (assuming that a full yield strength is not required) and the cog portion contribution conservatively assumed to be 0.5 L_st even though the cog portion contribution is actually 0.5 Lsy,t (> 0.5 L_st).

If I am evaluating the anchorage capacity of a rebar (in an existing structure) with a standard cog having a horizontal anchored portion (measured to the outside of cog) of length x (where x < 0.5 Lsy,t), is my total anchored length = x + 0.5 Lsy,t or is it 2x ?

RE: AS 3600-2009 Clause

I would say that if x is less than 0.5 Lsy.t then x = 0.5 Lst. Therefore, from, the stress than can be developed at x, sigma_st = fsy (2 x) / Lsy.t. It's perhaps conservative but it's defensible with a literal reading of the code. The development length of a hook is empirical so I would tend to be literal with the reading.

As a check you can look at it the other way around. Say you only want to develop half the yield strength of the bar. That would make Lst = 0.5 Lsy.t. With your first interpretation that would mean that with a look x could be zero (the end of the cog) since the remainder of the hook would develop 0.5 Lsy.t.. That wouldn't seem unreasonable. Your second interpretation would give x = 0.25 Lsy.t.

RE: AS 3600-2009 Clause

look = hook

RE: AS 3600-2009 Clause

You can only use a development of greater than .5 if you increase the bend radius to 10db or greater (clause

If you use the bend radius defined in the standard hook ( .5 is the maximum capacity of the bar you can develop, not matter how long the leg is past the bend. This is to limit concrete crushing with the curve.

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