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Arch Pipes


Typical Arch PipeModeling an Elliptical or Arch Pipe

Starting with HydroCAD 9.0, arch and elliptical pipes are available on the culvert, reach, pipe storage, and Tc screens.  Just enter the pipe dimensions and you're done!  And HydroCAD-10 includes a build-in table of common pipe sizes, automatically setting all the parameters for complex pipe-arch and elliptical shapes.  Users of earlier versions are urged to update to the latest version to get the lookup table and native support for a full range of pipe shapes.

What Dimensions Do I Need?

In addition to the width and height, you must specify the top and bottom radii for the specific pipe you plan to use.  (For an elliptical pipe, the top and bottom radii will be the same.)  Although you may commonly refer to these pipes by just their width (span) and height, the radii can vary significantly depending on the pipe design, material, and manufacturer.  The exact width and height may also be different from the nominal dimensions.

bulletWith HydroCAD-10, select one of the standard pipe sizes from the drop-down list, and all the dimensions are set automatically.
bulletFor earlier versions, consult the pipe manufacturer's specifications for the actual span and height, as well as the top and bottom radius.  For an elliptical pipe, adjust the top/bottom radius until the cross-sectional area matches the manufacturer's published value.

After you enter the width, height, and radii, HydroCAD will automatically calculate the corresponding corner radius.  If the entry screen says "no corner solution" is generally means that the top and/or bottom radii are too small to allow a smooth (tangential) connection between the corner and the top/bottom of the pipe.  In some cases, you may need to increase the manufacturer's radius very slightly in order to enable a corner solution.  If you are having trouble getting started, try entering these sample values to see how the entry screen works:

    Width=36"    Height=22"   Top Radius=19"   Bottom Radius=51"

Common dimensions can be found in the following sources:

Corrugated Steel Pipe:

Pipe Arches, NCSPA web page
Modern Sewer Design, 3MB PDF by AISI,  See tables 1-6 to 1-10

Reinforced Concrete Pipe:

Hanson Concrete Arch Pipe PDF

True Ellipse Pipes

HydroCAD-10 build 8 adds the ability to model a true ellipse shape, which can be oriented with a horizontal or vertical major axis.  Note that an elliptical pipe is a pseudo-ellipse, generally having a fuller profile than a true ellipse of the same overall dimensions.

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