New opening in exiting wall

[Okiryu]

Hi, I move this thread to the structural forum (it was in the demolition forum) since I think that people looks more at this forum....

We are doing a preliminary study for addition an opening in a wall for an existing tank. The existing wall is very thick (2 m thick) concrete wall. The tank is about 5 m height and we are planning to do the opening at the bottom of the wall (the bottom of the opening is close to the bottom of the tank). The opening is about 2 m by 2 m to allow for an inspection pit/box for pipes. Any references or input about the considerations for analysis/design/construction of this new opening will be appreciated.

 

[TehMightyEngineer]

We have a demolition forum? (Sarcasm)

I'd say the biggest issue is ensuring the remaining structure has sufficient strength. At 2m thick (wow) it likely does and is also likely able to easily support you cutting holes in it.

I presume you have the original reinforcement drawings for the tank? My first step would be to analyze the tank with the proposed 2m x 2m opening. For myself I'd use a simple FEA model in RISA but you could reasonably do this via simpler calcs assuming the meter or so of concrete above the opening is taking not only it's unit tributary width of load but also is now supporting the loads of the 2m of tank wall you removed. You'll also have high corner forces on the opening but at 2m thick I doubt corner cracking is a big concern.

For the demo (if that's in your scope) I'd recommend sawcutting your finished opening size on each side (likely cutting the reinforcement in this step) and then using drills or pneumatic chisel tools to roughly demo through the opening. The interior of the opening can then be cleaned up with pneumatic tools to be flush with the saw cut sections. Some consideration to corrosion protection of the exposed, cut rebar is in order.

I assume once your opening is cut you're filling it with pipes and other stuff but will need to fill the annular space with something to make the tank waterproof again. Probably just a butyl rubber seal around the pipes and such and then fill the space with grout, but depending on things you may need something more robust or leak proof.

Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA, FL) Structural Engineer (IL, HI)

 

[Okiryu]

Hi TME, thanks for your reply. So basically, your suggestion is to check the stresses in the vicinity of the opening based on the new wall configuration with new opening. I think that in our case, DL are more critical than the LL. Also, could you expand about this statement "...but also is now supporting the loads of the 2m of tank wall you removed.". Thanks again !