Oops - contractor cuts through opening reinforcing in existing wall 3

[jrfroe]

We have a project with an existing rectangular concrete tank that has a stainless steel lining (so concrete is not critical for tank being water-tight) and we needed to install a 6" pipe through the tank wall. We expected the contractor to core a small hole just above the tank floor through the wall to install the new pipe, but found that they instead cut a 24"x24" square opening through the existing tank wall. The biggest problem is that the cut opening is just below the corner of an existing manway.

The manway opening is a square opening about 3'x3'. The new cut opening overlaps horizontally with the the manway opening by about 3" on one corner. There is about 6" of concrete left between the top of the new cut opening and the bottom of the manway.

I'm mostly concerned because the vertical opening reinforcing on one side of the existing manway has been severed and I don't think its feasible to completely restore the strength lost in that area. I'm suggesting installing epoxy rebar dowels with as long of an embeddment as possible (I'm thinking 18") to attempt to get some semblance of a lap. This wouldn't give the same strength as the original and I'm guessing the wall might crack a bit from flexural stresses and redistribute around the affected area. The contractor is already balking at this idea (he wants to install a steel frame in the opening).

Has anyone else encountered a similar situation or does anyone have any ideas for alternative repairs that would restore the strength lost from cutting the opening reinforcing?

 

[miningman]

Was the contractor given clear drawings showing what you expected of him.? Hole dimensions and location of holes?? If not , I'm not surprised he is balking at any and all corrective actions.

 

[r13]

If there is inner tank, the cutout section might not even be required. But I don't know the layout, geometry, and the cutout section's location in relation to the manway, thus unable to justify my guess. Agree with miningman, your office seems dropped the ball.

 

[jrfroe]

Miningman - That is indeed part of the problem... they were not given clear drawings showing what was expected, so we are also partly to blame (which complicates things a bit). However, neither myself or any of our structural engineers were made aware of this project until after this hole was cut.

 

[JAE]

Do the manway walls connect in with your tank walls and provide some level of stiffness for the tank walls out-of-plane?

 

[jrfroe]

retired13 - the inner stainless steel is only a lining... not structural... the wall the hole was cut in is roughly 50' long and 12' high.

 

[jrfroe]

JAE - the manway has an embedded steel frame around it... There are no nearby out-of-plane concrete walls. The flexural stresses in this area are almost exclusively in the vertical direction (stressing the inside layer of reinforcing)

 

[IRstuff]

Where is the pipe relative to the new hole? It's 6 inches, so there's 9 inches of clear air on either side?

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[r13]

I guess this is not a cantilevered wall design. 2' cut out of 50' length may not present a big problem. Again, the description is not clear enough, can you upload a photo taking from afar? What is your position/function in this project?

 

[jrfroe]

IRstuff - The new pipe would be centered in the new opening. We would fill around the pipe with concrete after installing rebar dowels.

 

[jrfroe]

retired13 - correct... not cantilevered since it does have a roof bracing the top of the wall... I agree that its not a big problem for the tank as a whole as its a small section of the tank wall, but I'd expect extensive cracking locally in the area when the tank is re-filled (without any repairs). The project is design-build, so our firm holds the contract with the contractor doing the work.

 

[r13]

I agree, you can't leave it open. Good luck.

 

[SlideRuleEra]

jrfroe - How thick is the concrete wall?
Do you have details on existing reinforcing steel?

http://www.SlideRuleEra.net

 

[jrfroe]

SlideRuleEra - Its 12" thick with #6@12" each way & each face... I'm proposing to add in dowels of the same size and spacing with an additional dowel lined up just outside the edge of the manway above.

 

[bones206]

I've resolved similar situations by analysis. I would just checked the wall "strip" on each side of the opening for the additional tributary load. If the numbers checked out, I would accept it as-is. That's the easiest field solution.

Adding a plug of concrete back in with dowels may not necessarily hurt anything, but like you said it wouldn't restore full flexural capacity. Might be worthwhile just to reduce the stress concentration effects of a square opening. Especially an opening near a hatch.

 

[BridgeSmith]

I'm not sure I understand the configuration, but rather than trying to lap new reinforcing, I recommend mechanical rebar splices. The bypass type splices don't require much exposed length. See the "Coupling Sleeve with Double Wedge" type here. The single wedge type will also work, but typically not economical for small jobs, since they require a specialized press to wedge the pins.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[SlideRuleEra]

jrfroe - A 12' high wall that is 12" thick is not going to flex much from hydrostatic loading (triangular load profile zero load at the top). Suggest only a few dowels (maybe 6 or 8, total), positioned in the middle of the 12" thick wall (to miss existing rebar), and be satisfied if 18" hole depth is unobtainable (I'd be happy with half that depth).

Be open minded to change when repairs begin. Existing conditions dictate the as-built repair details, not the Engineer.

http://www.SlideRuleEra.net

 

[r13]

Be open minded to change when repairs begin. Existing conditions dictate the as-built repair details, not the Engineer.

Fully agreed. Be thorough but picky. Just for example, the reduction in wall force resisting capacity is reduced [(50/48)-1]*100 = 4.2%, which can be easily made up by the huge load factors usually applied to the design on water containers. I would say, detail maybe is more important than build up the strength for this case. Keep it simple.

 

[jrfroe]

Thanks everyone for your helping me chew on this for a bit! Much appreciated!

 

[Settingsun]

I don't think you need to give ground on who's at fault. The opening move is to get them to state how they intended to make good the cut they made, or who signed off the structural modification (cutting reo). They can't inflict wholesale destruction just because you didn't say not to. They're a capable contractor that knows the importance of reinforcement - can't reasonably deny that.