Pile Cap Loading in Pile Supported Wall

[CWEngineer]

Trying to get some clarification/guidance regarding the loading on a pile cap. Please see attached drawing for reference. Basically the pile supported floodwall was design with continuous longitudinal reinforcement in the pile cap. The pile cap has longitudinal and transverse reinforcement, for the temperature/shrinkage reinforcement and applied loads.

Currently working on extending the pile supported floodwall and installing dowels in the pile cap to meet the continuous longitudinal reinforcement requirement in the pile cap. But I am getting feedback that there is no load transfer in the pile cap connection. I guess I am having a hard time understanding, how in the original design, reinforcement (transverse and longitudinal) was required in the pile cap, I am assuming because there were applied loadings in the pile cap. But now that you are connecting a new pile cap section into the already constructed pipe cap, now there is no load transfer or loads applied at that location?

Appreciate if you can help me clarify this.

 

[JAE]

So when you add to the length of the existing pile cap - the new pile cap will serve as a continuous beam over the pairs of piling. This will require longitudinal top and bottom bars to resist the applied loads - mostly from the wet weight of the concrete wall above. Once the wall above hardens, the entire section (cap and wall) will tend to act as a stiff beam system spanning over the piling.

I am not sure what the dimensions and proportions are of the cap and wall system relative to the spacing of the piling - but you might have a deep beam condition here once the wall hardens.

Also - the wall, as a floodwall, is probably taking lateral forces perpendicular to the wall so the cap will act as a transfer beam between the paired piling.

When you add on to the existing cap, it is uncertain whether you can successfully tie into the existing cap with enough rebar and depth of rebar to establish a continuity between the two. With the expansion joint between the existing and new wall, you will have some possible rotation at this joint - so trying to get a continuous connection there (full moment connection) may not be possible and also may not be even needed.



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[KootK]

I agree with JAE...I think. At most, you've got a shear transfer joint there with respect to lateral loads. The pile layout that you sketched would seem to have anticipated that.

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.

 

[JAE]

Yes without the pile spacing and other relative geometries it is hard to know what the joint is doing but at the least it would be perhaps transferring vertical shear across the joint.
It may be that the pile cap arrangement shown is a double cantilever over the piles meeting at the cantilever tips such that vertical shear is small.

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[CWEngineer]

Yes, the feedback that I am getting is that the CIDH piles have been laid out such that no load transfer will be required across the joints (floodwall to bridge abutment stub wall & floodwall to existing floodwall). This was achieved by placing a pair of CIDH piles at a minimum spacing of three pile diameters. The newly constructed floodwall will act as an independent structure of the existing floodwall and existing bridge abutment stub wall.

Please see attached document, with additional details.

Based on this information, does it seem appropriate that there is no load being applied at the two connections (connection with bridge abutment stub wall & connection with existing floodwall)? My though is that supporting calculations are required to support this statement? The bridge abutment stubwall, might transfer loads to the floodwall and vice versa?

Thanks,

 

[CWEngineer]

Additionally feedback that I am getting is that the segments are spaced such that the spans at each end of this segment of floodwall are cantilever. By definition, the free end of cantilever has zero moment and zero shear, therefore, there will be no load transfer between the new wall segments and existing floodwall on one end and bridge's stub wall on the other end.

If there are smooth dowels connecting the existing bridge stub wall to the new floodwall section and deformed bars connecting the new floodwall section to the existing floodwall, is that considered a cantilered situation, specially when you have construction joint with rebar going through?

Thanks

 

[KootK]

By definition, the free end of cantilever has zero moment and zero shear,

The zero moment assumption is correct but the zero shear assumption need not be. Your joint sounds as though it could be expected to transmit shear across the interface.

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.