Alternating Dowels and Reducing Hook Development Lengths

[jochav52802]

Good Afternoon,

A few quick questions regarding reinforced concrete design per ACI 318-14:

1) Is it a requirement to alternate the dowel legs that enter a slab from a supported wall, or can the dowel legs be on the same side? If not, why is this done in practice? I have a slab that requires a 90-degree hook, but I don't have enough room in the slab to have the hook face outwards.

2) For a 90-degree dowel hook, when more reinforcement has been provided than is required, is it possible to reduce both the dowel hook longitudinal and lateral hook length proportionately to the ratio of required steel-to-provided steel? I don't see this spelled out in the code.

Many thanks for your help; I can't locate an answer on this within ACI 318-14.

Best regards,


jochav52802

 

[KootK]

1) I know of no such code requirement or requirement based on detailing fundamentals. When the hooks turn in outwards, I think that we do that simply to give more stability to the wall cage during construction. When the hooks turn inwards, I think that we do it to provide a nominal amount of moment resistance bi-directionally.

2) My interpretation is that any development length reduction has to come from the developed length without modifying the hook dimensions. Obviously, if you can shorten the development length so much that a hook is not longer required, that's a different scenario.

 

[bob33]

1. If you are transferring a moment from one to the other, the dowel should follow the moment around the corner. Otherwise, I don't think it matters.
2. Not a good idea to shorten the minimum lengths required by code. This would affect the ability of the bar to yield before the surrounding concrete failed. On the other hand, bars not required to resist real forces (nominal bars) are fair game.

 

[jochav52802]

Thank you for your comments!

 

[etimm]

2) 25.4.10 pg 427

 

[JoshPlumSE]

When you have bending towards the hook, the extra confinement provided by the hook arrangement is desirable. Hence this would be considered good detailing. Therefore, if you can have bending in both directions, then alternating the bars would be providing some level of confinement in both directions. So, it seems like good practice to me. But, certainly not required.

Note: ETIMM's post seems to be related to the concept of providing reduced development lengths for hooks based on As reqd / As prvd.... provided you still have 8db or a 6 in minimum.