Compression Piles in AASHTO 1

[WARose]

Question for someone who does a lot of bridge design........


In the IBC 2012, there is still a way for you to have the reinforcement in a cast-in-place, concrete pile terminate at a point (and just have a single bar going down the center) where the pile will always be in compression only and has little moment. (I've typically fought this approach.)

But in the AASHTO code, I really don't see a way to do that. It appears to me that you need the 1-0.5% minimum at just about all cross sections. For those of you familiar with this code (and I don't have the latest): is that how you see it? Do you need to have "the cage" at all cross sections? Is that what you typically see for anything getting traffic loads?

Thanks.

 

[BridgeSmith]

I think it's talking about the level below where there is relative movement of the soils due to seismic waves, i.e. in extensive bedrock that all moves together.

 

[WARose]

Right....but they exclude socketed piles with their exceptions. (Possibly based on bearing.) So I'm not sure what to make of it.

 

[BridgeSmith]

I think for the most part it's one of those things that everyone ignores for one of 3 reasons:

1) They're not ever really sure that there won't ever be lateral loading (that would be my excuse)
2) They're never comfortable using unreinforced concrete for anything structural (I'm in that camp, too)
3) They're not quite sure what the specifications are really saying.

Most bridge designers, I think, just overlook it like many other things in the spec. I just reviewed a proposed change to the section covering driven timber piles. Over the 8 editions of the LRFD spec. the driving stress limit equation has changed between a reduction factor of 3 to no reduction at all 4 times. What's worse, the section contains a reference to another subsection of the spec. that doesn't exist. It's been that way through 4 editions and several interim revisions over 10 years, and apparently no one even noticed. It seems no one uses driven timber piles anymore.

 

[WARose]

Thanks for your help in this HotRod.