Understanding percent part full design in pipes

Product(s): StormCAD, SewerGEMS, SewerCAD, CivilStorm 
Version(s): V8i, CONNECT Edition
Area:  Calculations

Problem

How is the percent entered for part full design taken into consideration?

Solution

When part full design is chosen design capacity is calculated as the capacity of the pipe at the depth based on your entered percentage. So for example if you enter 80% for part full design, it will solve Manning’s equation for flow at a depth that is 80% of the pipe diameter. This is compared to the calculated flow to size the pipe during constraint based design.

To confirm that this is working, take a pipe (after running constraint based design), note the diameter (or rise, if not circular), then multiply that by the part-full design percentage (for example 80%). Take the resulting depth value along with the pipe size, roughness and slope, then solve the Manning equation (you can use FlowMaster for this if needed) to get the normal-depth flow. This is the value you should see for the "Capacity (Design)" in the Results section of the conduit's properties. Take the actual computed flow through the pipe and divide by the "Capacity (Design)" and you should get the percentage you see for the field "Flow / Capacity (Design)".

When using standard design practices, the pipe capacity is based on full pipe, normal depth i.e. the flow in the pipe when the depth is 100% of the pipe. When we use partially full design, the designed capacity of the pipe is for a design depth that is only a portion of the pipe rise. A pipe that is designed for 50% full will be selected based on a depth of half of the pipe's rise. Hydraulically, the capacity at a percentage of pipe rise is generally not equal to that percentage of the full pipe capacity. 80% full capacity does not equal 80% of the 100% full capacity.

If you are running a design analysis, capacity (Design) should be used as it referred the percent full entered to calculate the capacity of pipe. Whereas Capacity (full) is the normal full flow depth of the conduit. To see that it is actually working correctly, you can compare "Capacity (Design)" to "Capacity (full flow)".

Note: when using the table-based option in the design alternative for part-full design (to specify different desired percent full for different size pipes), the "rise" values entered in the table are in reference to the actual, internal rise of the conduit catalog entries, which may be different from the "label". For example you may have a "250" entry in the conduit catalog, with an internal diameter of 188.2 mm. Ensure that you enter a value of 188.2 mm in the table in this example case.

See Also

Order of constraint based design priorities for StormCAD (GVF-Rational) and SewerCAD (GVF-Convex)

What is the difference between Capacity (Full Flow), Capacity (Design), Capacity (Excess Full Flow), and Capacity (Excess Design)?

Recommended
Related