Wastewater Treatment Plant - Launder Trough - Drill & Epoxy 1

[JoelTXCive]

We have a wastewater treatment plant under construction and the contractor has submitted and RFI for the launder trough in the clarifier tank.

They would like to replace the connection below with a drilled & epoxied connection. The loads are light. I have not done the calc in a while, but if you take the moment and resolve it into a force couple, then the tension is less than 1 kip per wall foot around the perimeter.

My hang-up on approving the change is that it's a sustained tension load; and I thought epoxies were subject to shrinkage when in sustained tension.

What do you think?

To add fuel to fire......my old boss approved this exact RFI with the same contractor 3 years ago; so I'm sure to get a bunch of blowback from the contractor if I reject the RFI. (which is what I'm leaning towards)

 

[HTURKAK]

-The launder trough is at the interior side of the clarifier tank and the use of drilled & epoxied connection will not cause negative impact.
- The RFI , ( if approved ) should be negative change order for the contractor..

My opinion..









Tim was so learned that he could name a
horse in nine languages: so ignorant that he bought a cow to ride on.
(BENJAMIN FRANKLIN )

 

[wrantler]

In general.. I do not have an issue with epoxy anchor systems. I do though have issue with the QC involved during the install - it needs to be religiously followed.

If I use epoxy anchors I like to spec some type of QC system..usually along the lines of having them test some of the anchors.

 

[JedClampett]

First of all, I've done several (hundred) of these. No matter how you detail it, the contractor wants to do it the other way. I've detailed lapped bars and they don't like it (forms). I've detailed couplers and they don't like it (cost). And just because your boss accepted it, does not mean it's a legacy permission forevermore.

But if you're not comfortable with it, ask them for a credit. "You bid it according to the design which showed couplers or laps. If you're saving money, you need to share." What usually happens is that they don't want to credit doodly, offer a couple hundred dollars, and you can present that to the owner.

The design of these is kind of trivial. When they're empty, the dead load controls. but when they're working, the buoyant force almost negates that, and forces are pretty small. But there might be a case when they're full of water and there's no buoyancy (probably impossible), so that might create a decent force.

 

[KootK]

My hang-up on approving the change is that it's a sustained tension load; and I thought epoxies were subject to shrinkage when in sustained tension.

This is something that I still haven't gotten fully sorted in my own mind. Consider:

1) Plenty of common applications involve using epoxy bar development in bending applications. Footing extensions etc. The Hilti literature deals with such situation explicitly.

2) Pretty much all flexural applications will see the bars subject to some degree of sustained load.

Based on that, there must be some "out" for the big dig issue. Perhaps:

3) It's less of an issue for flexural applications than direct tension or;

4) The issue is mitigated if sustained tension demand is some amount less than the yield strength of the bar or;

5) Epoxies have been developed that don't have this problem.

Separately, this is an application where I'd like to have a shear key. Surely not a big deal either way if the load is trivial.