Seismic Design For Piles

[Reigh0820]

Hi fellow Engineers,

I have a question regarding the subject above. It is duly noted that we need to consider on our design of piles and caissons in seismic events in seismic zone 3 and 4 (UBC 97 Section 1809.5.1 & 1809.5.2). So, the piles and caissons alone must be designed to resist lateral displacements. But also, UBC 97 Section 1807.2 insist that these piles and caissons should be interconnected by ties to resist tension and compression.

with these being said, is it possible to just design the piles and caissons alone to resist lateral loads OR just design the tie beams and make the piles and caissons be interconnected and help each other in resisting the said lateral loads? OR it musts be designed both?

Also, in relation to this, if the pile system comes with designed pressure slab, is it possible just to use the pressure slab to connect the piles and caissons for the same purpose as the tie beam in addition to the designed purpose of the pressure slab? If this is possible, is this system will make the most efficient and most economical?

Kindly educate me.

TIA

 

[MotorCity]

A few items first. Put aside the '97 UBC and pick up a copy of the current code. Next, what do you mean by "pressure slab"? The piles and tie beams act as a system and as such transfer and share the load. The purpose of the tie beams is to distribute the lateral load to all piles so that they respond in unison. The tie beams will have an axial force to transfer the lateral forces and a vertical force from the slab above unless you provide a gap between the slab and tie beams. If your slab is thick enough, it is possible to contain the tie beams within the thickness of the slab or simply design your slab as the tie beam. You just need a way of sharing the load among all of the piles