Reduction of development length
Reduction of development length
(OP)
Let's say I have a footing that requires only the minimum steel but I am having a problem with developing these bars. If I make the footing wider, I get more development length, but the moment increases and the required area of steel increases.
If I only need say 0.25 in^2/ft, but provide 0.5 in^2/ft for the minimum, can I reduce my development length using ACI 318-05 12.5.3(d) using 0.25 in^2/ft for the required As (since that is what is needed for strength) or do I have to use the 0.5 in^2/ft in that calculation?
If I only need say 0.25 in^2/ft, but provide 0.5 in^2/ft for the minimum, can I reduce my development length using ACI 318-05 12.5.3(d) using 0.25 in^2/ft for the required As (since that is what is needed for strength) or do I have to use the 0.5 in^2/ft in that calculation?






RE: Reduction of development length
DaveAtkins
RE: Reduction of development length
RE: Reduction of development length
That is the question, though. Do I really only need to develop 30ksi? If so than I am not really providing the minimum steel, correct?
civilperson-
I understand about develoopment, but I am trying not to have to hook bars or provide mechanical anchorage in a lightly loaded pavilion footing.
I can't believe I'm the first person to have encountered this. I have a 2' wide wall footing with a factored bearing pressure of 2.88 ksf (like I said, fairly lightly loaded). I'm sure plenty of others have used 2' wide footings. I even tried bumping it to three feet to get additional length, but that bumps the moment up. I then tried making it 18" deep, then 24" deep, but then the minimum jumps up.
RE: Reduction of development length
Check the footing as unreinforced for stress and if you do need reinforcing, this will tell you exactly at what distance from the outer edge of the footing you need the first infinitesimal amount of steel.
RE: Reduction of development length
RE: Reduction of development length
Doug-
ACI says that any section that requires reinforcement must have a min of 0.0018bh in it (for footings). To me that is the min for strength calculations.
This is for a shearwall footing, so the soil stresses causing this are localized. I think I am going to try determining where I can get away with plain concrete (and stop hooking the bars in that region), and just specify hooked bars at the ends of the footing where the soil pressures are higher and I need it. Does that seem reasonable?
RE: Reduction of development length
RE: Reduction of development length
I just realized an error. I didn't change my bearing pressures to k/in/ft so my moment was coming up larger than it should be by a factor of 12. I guess this is a good endorsement for including units in calcs. Boy, do I feel foolish.
RE: Reduction of development length
RE: Reduction of development length
StructuralEIT: We all have those moments, no matter how good an engineer we are. And from what I have seen, you are a credit to our Profession.
Regards,
YS
B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...