Letral Load on Drilled Pier and Grade Beam Foundation
Letral Load on Drilled Pier and Grade Beam Foundation
(OP)
I need to design a drilled pier and grade beam foundation for a 1,000sf single family home. I have a soils report that provides the allowable skin friction which I will use to determine the minimum depth to support vertical loads (toe bearing is being ignored). To determine the minimum depth required to resist lateral loads I would like to use the constrained formulas provided for the design of embedded posts found in IBC 1807.3. My question is...is this an acceptable method of determining lateral load capacity for this type of foundation? Has anyone used this method for this type of foundation.






RE: Letral Load on Drilled Pier and Grade Beam Foundation
I've used L-pile, a Geotech analysis, ACI has a manual on drilled piers which discusses lateral loading designs and chapter 12 of the enclosed publication. I recommend using the enclosed simply because it is free and appropriate for drilled piers under lateral loads.
Closely spaced piers will shadow each other and a pier in the shadow of another will not resist as much lateral load. Also, for short piers, you get a rigid rotation of the pier where long piers go into a sinusoidal bending pattern.
If you want to keep it simple then you could probably get away with just using the embedded post calc but have a read through of the enclosed just to check some of your assumptions.
RE: Letral Load on Drilled Pier and Grade Beam Foundation
That said, I'd have no problems with the IBC method.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Letral Load on Drilled Pier and Grade Beam Foundation
RE: Letral Load on Drilled Pier and Grade Beam Foundation
I don't do pier & grade beam design - do you assume fixity at the top of pier or is it a pin?
RE: Letral Load on Drilled Pier and Grade Beam Foundation
Teguci thanks for the FHWA reference I will check it out.
KootK I could see how some experienced designers might just use there engineering judgement and be able to assume the drilled piers are adequate for the lateral loads on a small home like this. Unfortunately the last time I designed piles was for a bridge 15 years ago so I just don't have the experience with this type of foundation to do that. I do expect the loads to be relatively low so I was hoping to find a simplified design method.
Stenbrook thanks for the reference I will check it out. It looks like that may be the simplified method I'm looking for.
Ascats I don't usually do pier design either, that's the problem. I dont have Lpile so I'm going to have to do some hand calc's. I planned on using the constrained method to account for the fact that the piers are all tied together by a concrete grade beam and I would assume they are fixed at that point. My thinking was that designing them individually as apposed to as a group would be conservative. Of course the pile spacing would play a part in this. I planned on starting my design with a spacing controlled by the maximum concrete beam span I could get away with without stirrups.
RE: Letral Load on Drilled Pier and Grade Beam Foundation
I've seen hundreds of geotechnical reports for structures - homes, low commercial buildings, etc. - and seldom did any of the reports ever discuss lateral pressures - and the ones that did, talked about the grade beam/strip footing's lateral resistance.
A 1000 ft2 home - why are you using drilled piers? Unless your soil is really poor - or your frost penetration is really high, why would you not just use strip footings? If you are using strip footings (or your grade beam) - you will have passive pressure resistance to lateral loads - the beam/footings would be buried in the soil for frost protection or seasonal moisture change - and they have a width and thickness that would develop passive pressure. A single story 1000 ft2 home is not a bridge.
RE: Letral Load on Drilled Pier and Grade Beam Foundation
Stenbrook- do you know the name of the book that Czerniak figure came out of?
RE: Letral Load on Drilled Pier and Grade Beam Foundation
Check out for excel foundation programme - it has Czerniak's analysis. I've not used it, though. http://www.calculatoredge.com/structural/polefdn.h...
RE: Letral Load on Drilled Pier and Grade Beam Foundation