Issue with slotted hole dimension

[Surya77]

I am having a field issue with slotted hole dimensions. This is for base plate related to a 20 ft light post in a parking lot

The anchors are 1 in dia, so I specified 1 1/16 in x 2.5 in slotted holes.

By mistake filed drilled 1 1/4 x 2.5 and now they are asking me if I can buy them off. They are worried about schedule impact etc.

What do guys think.

 

[KootK]

This is similar to standard oversized base plate holes. You should be fine so long as you've got some decent washers on there.

The "accident" may have been a very deliberate attempt to introduce some field tolerance.

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.

 

[Lomarandil]

Well, do they still meet your structural criteria? I'm going to presume you've already considered that (both for your base plate/bolts and the light pole deflection criteria).

It's not uncommon to oversize (and by this, I don't just mean OVS holes) anchor bolt hole patterns to allow for placing tolerance. Typically, the contractor will install large plate washers that are field welded to the base plate so the bolt can still be considered a bearing connection.

If it doesn't adversely affect your structure, and they're willing to provide and field weld the plate washers, I don't see a reason for alarm.

 

[Surya77]

KootK,

//This is similar to standard oversized base plate holes//

But standard oversize holes are only 1/16 in larger than ordinary hole right? this is 3/16 in larger. (please correct me if I am wrong)

//The "accident" may have been a very deliberate attempt to introduce some field tolerance. //

I think u nailed it, they haven't paid any attention to detail. As this is simple post they took it for granted and now asking me to bless it.


When you say decent washer, does 5/16 in washer suffice? I think code requires 5/16 in (I don't have code handy, I am at site)

 

[Surya77]

@Lomarandil

yes I considered the impact of slotting in the design, I was just concerned about larger than code prescribed holes.

I will mention about welding the field washer. they will provide field welded washers

 

[KootK]

But standard oversize holes are only 1/16 in larger than ordinary hole right? this is 3/16 in larger. (please correct me if I am wrong)

I don't think so: Link

When you say decent washer, does 5/16 in washer suffice? I think code requires 5/16 in (I don't have code handy, I am at site)

Check this out: Link



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]

Just get some 1/4" plates - perhaps 4" x 4" in size with standard holes in them. Use them as large washers to cover the slotted holes and then once the bolts are
tightened down provide some welds on the four sides of the plates at each bolt.



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[Lomarandil]

Actually, now that KootK mentions it, I also suspect it may have been a deliberate move on the part of the contractor -- not taking quality for granted, just adding a grain of practical experience. In the end, you are the structural engineer, so you can decide whether or not it's appropriate for this situation, but I wouldn't raise a fuss unless you truly have a problem with the larger hole.

As for the size of your washer, that depends on the forces you're trying to transmit -- you'll have to run a quick calc for the washer and weld. Before I would go too far trying to optimize the thickness though, I'd check with your contractor. They may have a pile of those 1/2" or 3/4" formwork plate washers laying around that they'd be just as happy to use.

 

[RWW0002]

Check out page 14-6 and Table 14-2 in the AISC 13th Ed. Provided are some instruction on maximum hole diameters for anchor rods in base plates. Although slotted holes are not addressed, AISC is recognizing that standard oversize holes do not always provide adequate construction tolerance for base plates. I still recommend making sure you are comfortable transferring your loads through whatever detail you allow, but there is a precedent for extra-oversized holes in base plates with the use of plate washers (or even with standard washers in some cases - See footnote 3).

 

[Surya77]

@JAE, RWW0002 @KOOTK @ Lomarandil

Thank you all for your inputs and time. Really helpful

 

[BUGGAR]

If the Contractor did not follow the plans, you have the right to charge the Contractor for your costs in evaluating his proposed fix. If the cost to analyze the proposed fix includes the purchase of RISA 3d or equivalent to analyze the proposal, so be it. Contractor gets his proposal approved, you get new software.

 

[Surya77]

@Buggar,

That's a good legal point and may be true if the issue is major and there is no possible fix either through field mods or engg judgment.

Also as you know engineering and construction work together, I just cannot burn them for a small discrepancy like this.

In this case by talking to you guys through this forum I realized that its not worth to make a big fuss. This slips the whole schedule and as holiday week end is coming up, this can slide for couple of weeks