Strip Footing Required Reinforcement
Strip Footing Required Reinforcement
(OP)
To All,
I am designing a concrete strip footing. The thickness of the concrete is roughly 2.25'. This is set to match an existing railroad foundation nearby). I designed the main bottom reinforcing to carry the moment applied (#6 @ 6"). Also, I designed shrinkage and temperature steel in the other direction (top and bottom) by simply using 0.0018bh. My boss mentioned to place reinforcement in the top direction (same plane at the #6 @ 6") and he said there is a note in the ACI 318 code about using a percentage of the area of steel required for the main reinforcement. This is due to the high footing thickness and some reinforcement is needed at the top of the footing, however even if it is minimal. I cannot find this section and wanted to know if anyone out there has a direction to lead me. Thanks.
I am designing a concrete strip footing. The thickness of the concrete is roughly 2.25'. This is set to match an existing railroad foundation nearby). I designed the main bottom reinforcing to carry the moment applied (#6 @ 6"). Also, I designed shrinkage and temperature steel in the other direction (top and bottom) by simply using 0.0018bh. My boss mentioned to place reinforcement in the top direction (same plane at the #6 @ 6") and he said there is a note in the ACI 318 code about using a percentage of the area of steel required for the main reinforcement. This is due to the high footing thickness and some reinforcement is needed at the top of the footing, however even if it is minimal. I cannot find this section and wanted to know if anyone out there has a direction to lead me. Thanks.






RE: Strip Footing Required Reinforcement
You only need reinforcement where there is tension. As long as the top surface never goes into tension you should be ok without any reinforcing there as long as you can meet all of your shrinkage and temperature requirements in the bottom mat. If your footing thickness was so large that your shrinkage and temperature steel became unreasonably large at the bottom, it would make sense to have bars at the top face too.
With that said, for a thick section I could see having bars at the top surface as a matter of engineering judgement, but I'm just not aware of that being required by ACI 318.
RE: Strip Footing Required Reinforcement
Then again, he may not...
Mike McCann
MMC Engineering
RE: Strip Footing Required Reinforcement
RE: Strip Footing Required Reinforcement
Mike McCann
MMC Engineering
RE: Strip Footing Required Reinforcement
Why not check as plain concrete with this thickness? The majority of strip footings I see have only nominal longitudinal bars and no transverse bars.
RE: Strip Footing Required Reinforcement
RE: Strip Footing Required Reinforcement
We wee able to come with a solution though... thanks again for all the help.
RE: Strip Footing Required Reinforcement
RE: Strip Footing Required Reinforcement
Dik
RE: Strip Footing Required Reinforcement
RE: Strip Footing Required Reinforcement
Don Phillips
http://worthingtonengineering.com
RE: Strip Footing Required Reinforcement
Mike McCann
MMC Engineering
RE: Strip Footing Required Reinforcement
Dik
RE: Strip Footing Required Reinforcement
Except for residences that usually have integral stem walls with somewhat effective "top" steel, I still feel, regardless of any code issues, that it is good to have top steel in any footing, particularly grade beams, to span any soft spots in the underlying stratum. Without this steel, considering the placement of the steel, it is very hard to develop the negative moment to prevent cracking of the foundation with any settlement. Regardless of the cost, which is minimal with any project, it is very cheap insurance against being dragged into court over cracked foundations. I usually design the foundation footing to span at least 10 feet to account for any settlement, or outwash due to flooding. I realize this is not required in most circumstances by most geotechs, but I consider it good engineering practice.
Mike McCann
MMC Engineering