Area of RCP Arch Pipe

[dicksewerrat]

I need help. I have a table for arch pipe to round equivalent pipes.What i need is a formula for the area of the arch pipe.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[CarlB]

Some arch pipe data here-

http://www.concrete-pipe.org/manual/CHAPTERS/CH 5.pdf

 

[dicksewerrat]

thanks CarlB

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[hoi1hoc10]

Actually, there is no formula to calculate the arch pipe. I had the same question as you have, but I find the answer my self. You can find all size of the arch pipe including the pipe area in the “Hank book of Steel Drainage & Highway Construction Products”. Each given arch pipe you will find the top radius (Rt), bottom radius (Rb), corner radius (Rc), span and rise. With these data, you can use AutoCad to draw the cross section of the arch pipe, and use the command “area” in AutoCad to determine the arch pipe area. Good luck!

 

[civilperson]

Equivalent arch pipe has same area as the nominal pipe it is replacing.

 

[RWF7437]

Are you sure CivilPerson ? If what you say is true shouldn't the equivalent pipe diameter be some odd number, such as 34.33 inches ? Doesn't equivalent, in this context, mean same hydraulic capacity as measured by area, hydraulic radius and Manning's "n" value ? Don't know, just wondering.

 

[RWF7437]

According to the American Concrete Pipe Association, Design Manual, 1974 Edition:

A 73" span x 45" rise RCP arch has a waterway area of 17.7 sq. ft. and is "equivalent" to a 60" circular pipe which has a waterway area of 19.6 sq. ft. In other words, it is just a close match.

good luck

 

[civilperson]

The maximum flow in the 60" circular pipe occurs when flowing with 0.8 of full height. The maximum flow in the equivalent arch pipe at the same slope is of the same magnitude and actually hydraulically very close, (same Q in CFS).

 

[RWF7437]

Again, referring to the ACPA Design Manual, page 198, maximum flow in a circular pipe occurs at a depth near 0.90 full and has a flow equal to about 1.08 times the full flow.

A 60" pipe flowing full would carry about 90 cfs at a slope of 0.001 ( n= .013) (page 182)

A 45" x 73" pipe arch at the same slope and "n" carries about 72 cfs ( page 194).

A 60" pipe
maximum capacity is about 1.08*90 cfs = 97 cfs

I do not know, but it seems probable that an arch pipe would have similar characteristics as a circular pipe for flows at or near full because the top inside of the pipe is, in fact, a circular arc. If that is so we might expect the arch pipe to carry about 1.08 * 72 cfs = 78 cfs when flowing between 0.80 and 0.90 full.

For practical purposes this may be close enough but, the difference seems to be plus or minus 25%.

 

[RWF7437]

http://www.hancockconcrete.com/plates/mndot/s3014j1.pdf