construction tolerances of steel pile caps and structural steel

[tab101]

Hi all,

I'm working on a construction project with steel pile caps and I've only ever worked with concrete pile caps so I'm a bit unsure of how to deal with this issue.

In terms of vertical tolerance, normally with concrete pile caps, the cap is poured low (eg 50mm below steel base plate), the base plate is precisely set so top of steel is correct and grout is used to make up any deviations.

Here, the design has structural steel being landed directly on steel pile cap. We have one contractor doing the piles & pile caps with various tolerances (say +/- 5mm for top of pile cap elevation for this example) and then another contractor fabricating and erecting the steel, with their own tolerances on both fabrication and finished steel level (say +/- 5mm).

So my concerns are, how should compounding tolerances dealt with? For example, if pile caps are 5mm high but within tolerance, and the steel fabrication is 2mm too long but within tolerance, so the top of steel is 7mm too high, how should this be dealt with? I understand you could, for example, not fabricate until after pile caps have been installed and surveyed, but this isn't an option here. Going forward, we are having the pile caps to be installed slightly lower, as shimming is easier than having to cut and reweld. Aside from the technical issue, assigning responsibility seems commercially problematic.

Anyone have any experience in general around this sort of situation?

Thanks

 

[hokie66]

Not even sure what a steel pile cap would look like. If it is steel, I would think it is much preferable to have the steel contractor to do the work, rather than the piling contractor.

 

[tab101]

Essentially it's a steel plate welded to the top of the steel pile, with gussets between the plate and the pile. Don't disagree with you about the division of work. Unfortunately that's the way it was sorted before I got here so now I have to resolve the issues that arise.

 

[WARose]

So my concerns are, how should compounding tolerances dealt with?

Without more specifics......it's hard to say. But one thing I can say (and this would be applicable regardless of cap type): a good approach is to have plenty of "meat" in the design so that any tolerance problem can be met without redesigning everything. To use an example of a concrete pile cap: I normally have it [the design] thick enough to where if the pile comes in too high.....it won't be much of an issue (and you won't have to change top of concrete elevation).

 

[SlideRuleEra]

Tolerance bands do not have to be centered around the desired value. For example, a tolerance band does not have to be + 5mm. A tolerance band of say, +0 mm, -10 mm, or + 2 mm, -8 mm, is not only acceptable but sometimes more desirable for manufacturing purposes.

Like hokie66, I'm not familiar with steel pile caps, but if you investigate moving the tolerance band for one or both operations you may get more desirable results. As long at the tolerance band is kept the same (a 10 mm range in the above example) the cost impact should be minimal.

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[IFRs]

Presuming you are driving or vibrating the steel piles in, it should be reasonable to cut the pile off at elevation +0 -5mm and then have the steel structure laid on shim plates to meet elevation requirements for the structure it is supporting.