large bridge column supported by drilled shaft

[bpstruct]

Have a larger than required bridge column that is to be supported by a single drilled shaft. The problem is that the least dimension of the column is slightly too narrow to simply extend the bars from the drilled shaft into the column. As a side note, both the column and drilled shaft has plenty of capacity. My idea is to support a drilled shaft cap on top to hook the bars that won't fit in the column and extend the bars that will into the column a development length. Then I have hooked dowels from the column extending into the footing/ds cap. My question is this...what forces do I need to design the footing/ds for? It seems like there is really nothing much required to be carried by the footing. See attached. Any help is appreciated.

 

[BAretired]

The top of pile should be laterally braced in two orthogonal directions. Depending on the properties of the soil, this may be provided by passive soil pressure on the side of the pile cap.

The pile cap must be deep enough to develop any bars occurring outside of the pile area. In that case, a simpler detail might be to cut off all of the pile reinforcement 2" below top of pile cap and provide dowels for all of the column steel. The column may need more ties than you have shown.

Pile cap reinforcement would likely consist of nominal ties as the cap seems to be in compression throughout.

BA

 

[bpstruct]

The column section shown is misleading...the open circles do not represent the dowels extending into the footing. There is a capital that expands out larger at top and those are bars that extend into the cap supporting the bridge beams. There are actually the same number of column dowels as column bars extending into the footing/cap. Those bars are hooked. The bars extending up from the drilled shaft into the cap that do not fit within the area of the column are also hooked (just two on each side).

There is some flexure that needs to be transferred from the column into the drilled shaft....breaking forces, wind, etc. But I don't think any of that flexure is really needed to be carried by the footing itself.

I had intended to detail with some nominal reinforcing as you suggested...just need a second set of eyes. Thanks for the input!

 

[Qshake]

Consider your location and any seismic requirements. Typically, you'd want to have greater capacity in the drilled shaft to force any plastic behavior into the column. If you're not in a seismically active area this may not be a consideration though it's often used anyway.

Another consideration is definition of mass concrete. By arbitrarily increasing the column, you may be leading the contractor into the requirements of mass concrete placement.

Regards,
Qshake

Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

 

[BAretired]

I am not current with the latest codes, but I would expect that in a seismically active area, the top of pile would need to be braced in two orthogonal directions by grade beams. Perhaps others can confirm this.

BA

 

[bpstruct]

Very inactive area seismically. Thanks for all the feedback.