Lateral Force on Aerial Sewer Line 1

[nealt]

I am designing a sewer outfall line that crosses a stream just downstream of a dam. I plan to support the sewer line on steel piers, and will use rigid restrained joint ductile iron pipe. I need help on determining the lateral forces acting on the piers and sewer line resulting from flowing water. Worst case senario would be in the event of a breach of the dam. I expect the forces will depend on the flow velocity and unit weight of the water. I don't need help on determining the dam breach flood wave, just a formula or methodology to determine the forces acting on the piers and sewer line once the flow velocity is determined. Thanks for any help.

 

[RWF7437]

Possibly, you could model the piers and the pipeline as a bridge using the program HEC-RAS. It is free and can be downloaded at

http://hec.usace.army.mil.

It will also model the dam break scenario. May take some learning though if you haven't used it before.

Russ Faust
Salem, OR, USA

 

[nealt]

Thanks RWF7437, but I need to calculate forces acting on the peirs and sewer line, ultimately to determine the bending moment acting on the piers, not a water surface profile.

 

[RWF7437]

nealt,

HEC-RAS does a lot more than calculate water surface profiles. It also calculates forces on piers and can estimate scour, sediment transport and model dam breaks. If you've never used it go ahead and download it and look at what it can do. I don't know any other program that can do as much for free.

Russ Faust
Salem, OR USA

 

[nealt]

Thanks. I didn't realize HEC-RAS would perform force analysis.

 

[RWF7437]

You're welcome. Send me an email and I'll send you a PDF file summarizing the features of HEC-RAS 3.0 .

Russ Faust

rwf7437@attbi.com

 

[cvg]

why are you assuming the dam will fail? The dam is likely designed for the probable maximum flood which is an event very unlikely to ever happen. Common estimates of the recurrence interval of these type of floods is in the range of 10,000 years. Sewer lines should probably be designed for maybe a 100 year lifetime. It seems that a simple risk analysis would show that the it is extremely likely that a dam break will happen which will then cause a failure of the sewer line. The probability would be something like 0.00001. This should be a non-issue.