Pile seismic inertial forces for bridges 1

[Jean_Wong]

Good day!

For bridges, should the mass of pile or other foundations below ground surface be considered for response spectra or seismic analysis? Why or why not?

Thanks!

 

[MotorCity]

Portions of foundations located below grade do not contribute to seismic base shear. This is because they move with the ground and as a result, there is no acceleration of the foundation relative to the ground. So if A = 0, F = ma = 0. For structures located above ground, they will sway at a period and acceleration different from the ground. Think of it as the structure above ground is always trying to catch up to the motion of the ground.

 

[Jean_Wong]

Thanks for the answer! Very informative
Could you recommend a published reference for this so that I can show my senior? Thanks!