Mislocated Pile Cap Reinforcement

[VaStruct]

I just found out that last week the special inspector noted a deficiency at the site with regards to the location of the bottom mat of steel reinforcement for a 4-pile pile cap. Instead of installing the reinforcement 3" above the top of the micropiles (9" from the bottom of concrete), the contractor installed the reinforcement 3" clear from the bottom of the concrete of the pile cap. When the contractor was notified by the special inspector of this deficiency, he elected to proceed with the pour.

I've been looking around the web this morning and can't find any references to a condition such as this. The pile cap was detailed following CRSI which uses a strut and tie method. I noted that in Appendix A of ACI 318-08, part A.2 indicates that struts may only cross at nodes but that ties are permitted to cross struts. With the tie reinforcement placed below the top of the pile, it seems that there is some "eccentricity" in the strut and tie model that isn't really ideal. My concern is whether the strut and tie method is still valid for this configuration. Also, the shallow cover on the tie reinforcement could lead to spalling of the concrete and exposure of the reinforcement to corrosion.

Any thoughts on this would be appreciated.

Thanks.

 

[KootK]

Also, the shallow cover on the tie reinforcement could lead to spalling of the concrete and exposure of the reinforcement to corrosion.

Unless you think that you may not actually have the required reinforcing cover, I wouldn't be terribly concerned with this.

With the tie reinforcement placed below the top of the pile, it seems that there is some "eccentricity" in the strut and tie model that isn't really ideal. My concern is whether the strut and tie method is still valid for this configuration.

Strut and tie is probably more valid than usual in this situation. Just not quite the strut and tie model that the CRSI stuff is predicated upon. I'd see the following requirements manifesting themselves:

1) Slightly increased bottom bar extension required beyond the piles for anchorage (~9").

2) A small demand for tension resistance in the portion of the pile cap above the piles. Ideally that would be some top steel if there is any. Less desirably, you could attempt to make use of the concrete tensile capacity.



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.