Development length for Concrete Piers and Footings

[imsengr]

Hi everyone,

I am working on isolated spread footings for an industrial plant. I need to know the best way to calculate the development lengths for my reinforced concrete piers and reinforced concrete footings. I understand that you have to use a formulae to derive them now rather that saying you need so many bar diameters, for instance. I remember someone on this forum calling it a dog breakfast. I use mainly #10 bars for my 3' square piers (say, 12#10) and about #9 bars for my footings (say about 9#9 bars T&B EW for 8' square footing.)

Any sugestions, and useful references would be much appreciated.

Thanks, y'all and have a great weekend. Drive safe.

 

[JAE]

#9 bars for an 8' footing sounds like a too big bar to me. This doesn't address your question I know...the bigger the bar, the more difficult it is to get dev. lengths to work.

ACI 318 has all the development information needed for US applications (Chapter 12).

 

[DaveAtkins]

I agree with JAE--I do not think you can get a #9 bar developed in 45" (the bar must be developed in the distance between the end of the bar--which is 3" from the side of the footing--and the middle of the footing, where the moment is highest). For the pier, unless you have a lot of bending moment or significant uplift, I doubt you even need to develop the bars. And so I would use minimum steel in the pier (I try to use #6 bars or smaller in just about everything I do).

DaveAtkins

 

[civilperson]

Using ninety degree standard hooks at the ends or mechanical anchorage, (welded cross bar), you may succeed with the large sizes of bar that you have specified.
Horizontal bars with greater than 12" of concrete below require 30% more length for development. Try designing footings with unreinforced standards,(Chapter 22), and use vertical reinforcing in your piers equal to or less than the anchor bolt diameters for development at the anchor bolt lap.

 

[imsengr]

Thanks for the responses, guys, keep 'em coming.

I plan to bend the reinforcement 90 degrees at the ends, allowing for adequate cover, and let the reinfocement go to almost half the thickness of the footing. I have three types of footings, ranging in thicknesses from 36 to 49 inches. Wouldn't this be sufficient thickness to develop lenghts for both my pier and footing reinforcement? Hope you all can elaborate.

 

[civilperson]

Check out a ACI 318-05,12.5.1, "l" development length in tension of deformed bar with standard hook is 24.75 inches from end of bar to outside of bend, (hook), and requires 17.3 inches from outside of bend to point along bar where fully developed, (f'c=3000 psi, fy=60 Ksi and 2.5" side cover).