hook

[edwin17th17]

i am checking a pedestal and footing design.
the rebar on the pedestal has hook at the bottom
and at the top.. i understand the hook the bottom
but the top, is this still necessary?

 

[JAE]

I don't ever hook pedestal vertical bars at the top.

 

[jike]

Could it be for an uplift situation?

Hooks in the verticals at the top make it more difficult to pour the pedestal. An alternate to the top hooks may be separate hairpins or longer anchor bolts to overlap more with the rebar (if possible).

That would be my guess.

 

[edwin17th17]

i just talk to the originator he said because the development lenght is not enough..

is this correct logic.. i'm assuming you should extend the hook at the bottom to meet the development lenght..
not put hook at the top..

 

[edwin17th17]

development length was = 47db (aci.12.2.4)
but what he did was this length from top of footing to top of pedestal.. that's why he hooked it because pedestal is short..

shouldnt 47db be top of footing all the way to bottom of footing for development length

 

[jike]

Development length needs to happen above and below the joint between the pedestal and the footing. It can, however, be modified by the ratio of As required to
As provided.

 

[edwin17th17]

so he's wrong. it's between footing and pedestal. not going to the top it's useless and weird

 

[edwin17th17]

ok i got the idea but still a bit confused he was talking about double development length.. they should have the same developement lenght at the top and the bottom.. due to tension..

he has a point but somehow i'm not totally conviced..
what if the pedestal is too short and small that development lenght of 47db is not possible?

 

[jike]

If the pedestal is too short, you can use smaller bars (with less dev. length) or use more steel and then proportion down the dev. length by the ratio of
As required to As provided. Another option is to eliminate the pier and have the column sit directly on the footing.

Most pedestals have way more vertical steel then required and he should be proportioning down the dev. length by the ratio of As required to As provided.

 

[LOKSTR]

edwin17th17,

Hook at the top is sometimes required under following situations:

1. Uplift in the column
2. Size of pedestal is not ok for concrete breakout cone.
3. Rebar is provided in pedestal to prevent the splitting/breakout of concrete due to pulling out of anchor bolt. To transfer the tensile forces from concrete to these rebar, you need to have sufficient length to fully develop.
If the length can not be provided as per code requirements, then one need to provide a 90 or 180 degree hook.

 

[Bobber1]

We have to hook pile dowels into cap beams all the time to develop the dowels into the cap and keep the cap from pulling off right over the dowels.