Hooks in Cylindrical Reinforced Concrete Water Reservoir 1

[Robert-32]

In the structural details, all rebars are hooked. What is the reason? and can we use straight bars instead by adding additional length = development length of the bars?

 

[JedClampett]

For such a vague question from someone who's role is unknown (contractor, designer, checker, etc.), I'd say you need to provide more details.

 

[Robert-32]

Dear Jedclampett, Thank you very much for your reply. I will make my question clear, I am a structural designer who is looking at the design examples of cylindrical water reservoirs. I noticed that all bars have hooks at the end, and I was wondering why the designers did not just provide the required development length instead of the hooks? Is that related to earthquake design requirement? Is it just to cut the length of rebars? Or there is another reason that I am not aware of?

 

[JedClampett]

OK, I see now. The footing would have to be very deep to develop a #7 or #8 bar. Hooks are the standard way to develop bars at a slab wall joint.
Even though it's very old (1992), you should try to get your hands on the PCA Publication Circular Concrete Tanks Without Prestressing.

 

[hokie66]

I thought he was referring to the hoop steel. Otherwise, why emphasize that the tank is cylindrical?

 

[Just Some Nerd]

My first impression was in line with yours, hokie.

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Why yes, I do in fact have no idea what I'm talking about

 

[Robert-32]

It all steel not only the hoop steel.

 

[JedClampett]

I don't think I've seen hooks in hoop steel before. There might be a need for them at openings, but we usually just use our standard concrete opening details. Besides that, the hoops are continuous bars with enhanced lap lengths (due to them being in pure tension) and staggered.
If you had hooks in the hoop steel, it might affect the wall thickness. A #7 ninety-degree hook is 14 inches long. With cover, you're at an 18-inch-thick wall. And if you oriented them horizontally, it would be harder to get the stingers in the concrete.

 

[hokie66]

Unrelated, but in Australia, we don't call a 90 degree bend a hook. 180 degree bends are hooks, 90 degree are cogs.

 

[Robert-32]

 

[Robert-32]

The images above should clarify the post.

 

[JedClampett]

I'm not sure but scaling this might uncover some issues. those 180-degree hooks (thanks dik) aren't that tight.
Plus, maybe it's different now, but I got scolded (nicely) by a fabricator a long time back about too many bends in a bar. They say that it takes up too much room in the shop floor. I'm thinking of those diagonals with the 180-degree hooks at their ends.

 

[hokie66]

Jed, me, not dik. But you are welcome.

That drawing is indeed strange. Those 180 degree hooks, by scale, would not fit the definition given by any code of a hook. They are not long enough.

And yes, some of that would be a challenge on the bending shop floor.

 

[Just Some Nerd]

Might just be my inexperience talking but I'm not sure what the long horizontal ends with hooks on those vertical bars are doing. A standard cog length would work just the same for a 90 degree bend, no?

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Why yes, I do in fact have no idea what I'm talking about

 

[BridgeSmith]

I had the same question as Just Some Nerd. The diagonal cicker bars should only need to be extended at most the development length (straight)to prevent pullout. To prevent breakout, the diagonal cicker bars also need adequate embedment from the top of the footing.

I also don't understand the purpose of the hooks in the vertical bars above the construction joint. They should be lapped to the vertical bars from the lower stem wall, which is all they need to transfer the force across the joint. I don't see that the hooks there really accomplish anything.