ACI 318 - foundation deflection criteria? 1

[a2mfk]

I don't have my copy handy, does anyone know if there are criteria or limits to deflection of continuous wall foundations? I don't have a specific problem in mind, but the situation is a typical residential foundation. There are no such limits in our code (Florida Building Code), and I would not expect any in ACI.

To be clear, I am talking about soil-supported continuous wall foundations, not grade beams on piles or anything like that. And I know that even the term "deflection" doesn't really apply to differential foundation settlement to a soil supported foundation system, but this is the term I "have been handed" to comment on. I only need to know if this is mentioned in ACI 318 or not. Thanks in advance!

 

[Lion06]

No, it isn't - at least I've never seen it. Who asked you to comment on the "deflection" of a continuous strip footing? I've never even heard deflection used in that context.

 

[a2mfk]

Politicians did this to me Lion. Politicians. This is only the tip of my annoying iceberg.

 

[hokie66]

I doubt that you will find any code or guideline which gives limits on deflection or settlement of strip footings. For one, it would be impossible in most cases to determine if the "deflection" was built in or is the result of settlement and/or heave.

When footings move, that creates problems in the structure above. These are the measurable and codifiable criteria which mean something.

 

[a2mfk]

Agree completely Hokie. Just want to cover my bases and make 100% sure that its not in ACI anywhere. Like you said, its not of much use anyway. Nor is it the right terminology really. But this is bureaucracy not even created by our own kind (engineers).

Thanks guys!

 

[msquared48]

I believe the intent here is for a stem wall to be able to span over a section of soft soil, which can happen on any job - deflection understood here, but not really specified as far as I know.

I usually check the stem wall or strip footing for a 10 foot span for the load it sees to get by this periodic problem.

Mike McCann
MMC Engineering

 

[a2mfk]

Mike- are you aware of any deflection criteria for continuous wall footings in ACI 318? This is not for design, it is forensic related...

 

[Guest262653]

Just a small comment: this is what happens when lawyers start running the show.

Good luck!

 

[BigH]

From Tomlinson - Reinforced and Non-reinforced load bearing walls - which I believe is what you have indicated - see attachment.

 

[a2mfk]

avs- 100% accurate

BigH- That's good stuff, I had never given distortion of shallow foundations this much thought... But to be clear, this was not cropped out of ACI somewhere, this is from a textbook?

Thanks everyone.

 

[BigH]

Yes - this is from M.J. Tomlinson's very very good book on Foundation Design and Construction (6th Edition). Also in Day's Foundation Engineering Handbook (that is published by ASCE).