Underdeveloped reo hook: how much does the tail extension matter

[Greenalleycat]

I am assessing a weld plate detail beneath a braced frame in an old building. It uses D12 (sorry you imperialist, you're going to have to adapt to the metric system) with pretty shallow hooks
It's not dimensionsed but the overall length is 'ex 250mm' and it scales to approx 150x100 hook (150 vertical, 100 return)
The 150 vertical is actually OK, but the 100 return is less than the code requirement for 12db AFTER the bend radius (so we are ~80mm short)

Our seismic assessment guidance provides a means to assess underdeveloped hooks, but these are based on Ldh i.e. the vertical portion of the bar
I can't find anything that gives me good insight into the importance of the return, and what a lack of development means here
My gut feel is that it isn't as important as the vertical length, but I don't like to just assume things....
Anyone got any insight?

Also, why is this return length seemingly independent of the bar grade - it is only dependent on bar diameter, which is inconsistent with the calculation methods for other development (Ld and Ldh are both grade dependent)

 

[KootK]

My gut feel is that it isn't as important as the vertical length, but I don't like to just assume things....

That's my gut feel as well.

I can't find anything that gives me good insight into the importance of the return, and what a lack of development means here

I don't know with any code-ish certainty but my feeling would be:

1) Little impact on the compressive stresses developed within the bend.

2) Perhaps a lessening of the lever arm over which the compression stresses on the outside of the leg operate.

 

[DaveAtkins]

I do not have any reference for my opinion (i.e. I am just making an educated guess), but could it be the shorter bar extension allows for the bar to "unbend" and pull out of the concrete?