Pipe through corner of catch basin, how to analyze?

[soiset]

I've got a structural situation that seems apparently more than adequate from an intuitive standpoint, and certainly looks plenty strong to the untrained eye, but is pretty damned difficult to rationally model:

A rectangular catch basin with 6" thick walls is site cast around a 24" RCP with 3" walls. The interior dimensions of the catch basin are 32" x 62". The inside crown of the pipe is 27" from the top of the basin, and the flowline of the pipe is at the bottom of the basin. Pretty normal stuff, right? Well, here is the hard part: The pipe penetrates the corner of the basin at a roughly 45 degree angle.

Now I look at this thing, and I know it won't fail, but I cannot figure out how to model it. The only simplified solution I have is to figure each wall of the catch basin over the pipe as a cantilevered deep beam over the pipe. Seems like a pretty crappy solution, though.

Any thoughts?

 

[soiset]

OK, now I'm thinking I should use a strut and tie model, similar to a corbel. Sound reasonable?

 

[JAE]

Well...ahem...to me (with strut-and-tie) it sounds like you are waaay over analyzing a small little catch basin. Do you have truck wheel loads on this?

 

[SlideRuleEra]

RCP has significant structural strength. If a 24" pipe has a 3" inch wall, it must be at least Class III. The catch basin wall are not cantilevered over the pipe - they are supported by it.

IMHO, if the buried pipe run itself is adequate for the loading, then the wall that includes the embedded pipe is too. (Think of the concrete wall that encases the pipe as some "really good" backfill)

http://www.SlideRuleEra.net

 

[soiset]

I think both of you are right. I do have to account for heavy wheel loads on this, but it is apparently strong enough. It is Class III pipe, and it has plenty of cover.

The City of Houston flagged it, though, because it passed through the corner, which is contrary to their details, and I was assuming that they would want numbers to justify my contention that the system was structurally adequate. I'll stamp it without running a single calc, if they'll accept it.

BTW, there is no way they flagged it for hydraulic reasons.

 

[JAE]

If there's some amount of wall above the pipe, you could simply run some additional rebar around the corner, near the top (keep good cover though). I suppose you could put a truck wheel load right at the corner and see what sort of cantilever moment you'd get in each wall (1/2 of the load for each side)...then use the moment with some rationalized depth (with b = 6") and see about what As you get....but here I was chastizing you for analyzing it too much and then I tell you to analyze it....go figure.