Bridge Pier Pile Cap Top Steel

[VoyageofDiscovery]

I know it isn't common practice to connect column steel to cap top steel. Aside from the dowels that actually extend most the time to the bottom steel in the pile cap, how does a "fixed base" pier transfer its moment to the concrete pile cap. I would think this concentrated moment would create tension on the top surface of the cap near the perimeter of the pier column. I also have down drag on the piles.

Does anyone have insight on this?

 

[Qshake]

If my understanding of your question is correct, it is the rotation of the column/pile cap joint that places compression in the top surface of the pile cap in most cases. This, of course, results in tension along the bottom surface wherein the reinforcing steel is most commonly placed. However, when experiencing down-drag or any tension in the pile (should the client allow that) the footing as noted by AASHTO is idealized as a cantilever with the fixed end at the edge of the column. AASHTO instructs us to disregard the underlying soil and design as a cantilever beam. Since in many cases, the allowed (not allowable) tension on the pile is so small compared to the moment transfered from the usual loads that it is acceptable to place the same reinforcing in the top as that was designed for the bottom.

I hope that helps. If not please clarify.

Regards,
Qshake

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[VoyageofDiscovery]

Hi Qshake,

Thanks for your response. Neglecting pile drag down for now. Does the moment from a column at the top of the cap create tension at the top of the cap at or near their interface?

Regards

VOD

 

[VoyageofDiscovery]

Hi,

I've had a bit more time to think about this. The dowels anchor the tensile forces from the column vertical bars. This, in effect, accounts for the moment from the pier. Thus no tension in the top of the cap unless the cap is not thick enough or the dowels and its surrounding concrete result in anchorage failure.

I think I've answered my own question.

Thanks again.

Regards

VOD