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Re: (Tanks)

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On Dec 7, 2004, at 9:51 AM, Chad Van Kampen wrote:

This particular tank has been used since 1947 and not a one has had any problems.
I can't tell you how many times I've heard this or the variation 'We never had any problems before,' on all sorts of things, including tanks. There are only three reasons why this is the case--
1. The thing never saw the design loading
2. The figures you ran aren't physically accurate
3. The things really did have problems but they weren't reported.

Sounds like you're talking about a buried septic tank. There are a dozen reasons why some combination of 1. and 2. is probably the reason. Soil loading isn't terribly accurate and if the tanks were kept properly filled there won't be much net moment on the tank walls. The lid is another story--it always sees loading but if the soil bridges or the tank hasn't been driven over, there's probably some margin in the design. The real question is whether you can guarantee that the tank will always be filled and that it won't be placed under a roadway.

As far as sealing a drawing based on hearsay, I wouldn't dream of it, unless I could back up the reported performance with sound engineering calculations. Would you buy a used car based on the salesman's claim that they've never had any problems with it?

Christopher Wright P.E. |"They couldn't hit an elephant at
chrisw(--nospam--at)    | this distance" (last words of Gen.
...................................| John Sedgwick, Spotsylvania 1864)

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