Extending an existing waste water tank concrete wall
Extending an existing waste water tank concrete wall
(OP)
Hi,
I am working on adding another concrete tank aeration basin to an existing one. So the existing walls need to be extended. What do you recommend to consider in doweling into the old concrete? Since the tanks are going to be full, the tension in the corners add up, is simply doweling epoxy rebar into the old wall and extending it enough?
I am working on adding another concrete tank aeration basin to an existing one. So the existing walls need to be extended. What do you recommend to consider in doweling into the old concrete? Since the tanks are going to be full, the tension in the corners add up, is simply doweling epoxy rebar into the old wall and extending it enough?






RE: Extending an existing waste water tank concrete wall
Depends on how many dowels can be used. Can't just install as many as you want... have to look at the problem the other way around. Using manufacturer's (e.g. Hilti) technical recommendations, calculate what size, where and how many epoxy dowels can be installed. Then check to see if that is enough to safely resist the necessary forces.
If not, another solution may be needed.
Even if enough dowels can (theoretically) be used, the challenge is to see how many can actually be installed. Field drilled holes in existing concrete that hit existing rebar can cause a change in plans.
Of course, use an appropriate water stop between old and new concrete.
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RE: Extending an existing waste water tank concrete wall
RE: Extending an existing waste water tank concrete wall
DaveAtkins
RE: Extending an existing waste water tank concrete wall
RE: Extending an existing waste water tank concrete wall
About your additional concerns... On a retrofit job, like this, you often have to put aside what are real concerns on a new design. That is why the manufacturer's recommendations are used for calculations instead of ACI, or similar specs. A reputable manufacturer, like Hilti, has researched the capabilities of their products to maximize probability of success. Make sure the existing concrete is in good condition and make conservative choices on the details of your design.
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RE: Extending an existing waste water tank concrete wall
Keep in mind that simply developing the strength of a rebar into a concrete mass (a challenging task alone due to very deep embeds required) is not sufficient to ensure adequate joint performance.
A wall corner is the very worst location for a construction joint for a fluid-retaining structure, so a conservative approach is in order.
Design your wall plates so full continuity at the corners is not required (i.e. design for a pin, which will thicken your walls), because you won't realize anywhere close to even 80% efficiency. That is, your post-installed anchors should be shear-controlled.
And check shear-tension interaction.
RE: Extending an existing waste water tank concrete wall
RE: Extending an existing waste water tank concrete wall
Can I use regular epoxy rebars intead of Hiltis? The client insists of extending the basin instead of building a new one next to it. Also, the extended foot print of the foundation needs to connect to the new concrete, do you recommend Hilitis there since the development length will be an issue? Is it safe to assume all the shear is going to the rebars in the corner and make sure they can handle the load?
RE: Extending an existing waste water tank concrete wall