Seismic Mass of Pipe Piles in Water

[cancmm]

I have a situation where I'm analyzing a bridge bent that includes open-ended pipe piles driven through water. Would the water within the pile be included in the seismic mass of the structure? I'm inclined to say yes but can't find any explicit guidance on this matter. Note I'm considering this a separate issue from hydrodynamic mass.

Thanks!

 

[KootK]

I vote yes. To complicate matters, you'd probably get some voodoo sloshing action as well. I would expect the water's contribution to overall seismic response to be negligible however. Is that not the case?

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.

 

[cancmm]

Thanks for the vote. The piles are long and big, and the deck is relatively light, so we're evaluating how much of an issue it actually is. The contribution of the water increases the pile mass by 2.5x.

 

[JStephen]

For tank design, for a tall slender tank, most of the contents is treated as "impulsive mass", meaning it is assumed to move rigidly with the tank shell.
You'd presumably have some effects from the water outside, and might have some effective mass from water outside the pile as well.

 

[SAIL3]

I agree with JS......curious how the OP plans to handle the hydrodynamic mass?....

 

[TLHS]

I'm curious how you actually do the full analysis of something like this. In my mind the simplified approach would be to analyze the bridge structure without interaction with the surrounding water for the base seismic loads. Then add basically a wave case with water velocity hitting the structure with pressure on any submerged parts based on their drag coefficients, which should account for the earthquake driven water waves.

On the face of it, that would seem to be a conservative approach unless you get resonance between the structure period and the waves.

Without simplification, I can't picture a good way to actually model the situation. It seems like there would be too many different parts to get a good picture of the real behavior.