hook development of footing rebar

[delagina]

i was arguing with another engineer that footing hook development should be calculated as shown as Ld2 and not Ld1.

in my opinion Ld1 is should not be calculated if there is a need for a hook.

 

[dik]

Unless I'm missing something, I'd use Ld1... from the face of the support, or possibly from a 45deg angle from it (assuming a crack). The development length Ld1 should equal the bar development length.

From a theoretical point of view, it's not mormally a problem since the bond stress should reflect the shear force... starting at 0 on the outside to whatever at d/2 from the face...

Dik

 

[DST148]

@delagina: I do not know which code you are referring to. I am using ACI 318-05 as a reference.
With reference to your sketch, let us assume the critical section is at the left face of the vertical member.
Ldh = development length in tension of a deformed bar with a standard hook, measured from critical section to outside end of hook. The rebar needs to be developed on each side of the critical section and therefore, both of the following two conditions are required to be satisfied.

{Ld1(your sketch) - side cover} > Ldh
{Ld2(your sketch) - side cover} > Ldh
A similar check would be required at the right face of the vertical member. Moreover, the critical section for checking the development length depends on the material of the vertical member being supported by the footing, i.e. concrete, masonry, or steel.

 

[delagina]

i am basing my "logic" similar to a cantilever connected to a column. we only develop the column side not the cantilever side.

in the footing, cantilever side is the left side and the column is the right side.

if you will look at the pic of my OP how can you develop the Ld1 of the second case?

 

[TXStructural]

DST has it right. Reinforcement must be developed on both sides of the critical section, or more specifically, it must be developed any place the reinforcement is required. In flexural members, there are provisions for reducing the development length, such as excess reinforcement, but it still has to be developed.

In the top sketch, Ld1 would need to be developed; Ld2 should be developed before reaching the right side of the column, not the left. (the bar would need to be adequately developed anyplace it is required to resist demand.) Hooks are sometimes avoided because Ld is available and Ldh is not needed, with certain geometries and soil conditions.

In the bottom sketch, L1d might not develop on the near side of he column, but as drawn, it is undoubtedly not required. It would be required to be developed to the left before reaching the right side of the column. It would certainly be required to be developed to the right until the design does not require tensile reinforcement.