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Vibration of Reinforcement in Pipe supports

Vibration of Reinforcement in Pipe supports

Vibration of Reinforcement in Pipe supports

(OP)
Hi,

I have a Reciprocating Foundation as shown in sketch given below, unfortunately due to construction changes some pipe supports where attached in the later stage. If the dowels are connected to the foundation as shown also the plinth and the block is poured as a
single pour.
When the pipes supported over the plinth starts vibrating a crack would be formed between the plinth and the block.
So the rebars connecting the plinth and the block would be subjected to a cyclic tension and shear.
At some point of time a plastic hinge may form in the rebar connecting the plinth and the block and may fail in the later stage.
Please correct me if I am wrong and also please tell me an alternate solution.
https://res.cloudinary.com/engineering-com/image/upload/v1482940790/tips/PUMP_FDN_hrd3de.pdf

RE: Vibration of Reinforcement in Pipe supports

Your pic kind of confuses me a bit, but I would think that if the design is done properly the unbalanced forces any re-bar should see would be pretty minimal. I've done a lot of foundations for machines generating dynamic loads, and generally this was not an issue. Most of the time when I've checked re-bar fatigue, it's been when we are talking a pile supported slab and the unbalanced forces are generating moments in it (via 2-way bending).

RE: Vibration of Reinforcement in Pipe supports

(OP)
I dont know weather you saw all the three pictures, that is the PDF attached. The plinth is attached to the Block by steel rebars. My worry is fatigue due to cyclic loading from the pipe(since it is vibrating support). If the plinth is monolithic or rigid as the block foundation nothing will happen. Please correct me if I am wrong.

RE: Vibration of Reinforcement in Pipe supports

I assume the plinth is sitting on (or poured on) the ground correct (not a pile)? If that is the case, eventually I would think (due to settlement) it might be a cantilever off the edge of the pump foundation. The pump foundation (assuming I am understanding this drawing correctly) is sitting on piles.

I don't know how much unbalanced force we are talking here, but you may have to run some rough numbers to see what it would take to create unacceptable vibrations. (Or do a full blown dynamic analysis.) Just eyeballing it, I wonder more about motion than cyclic issues in the re-bar.

RE: Vibration of Reinforcement in Pipe supports

it seems this pump foundation is on piles, curious what software or excel or guideline you used for the dynamic analysis and resonance check. all the spreadsheets i have are on soil.

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