Reinforced Concrete Pipe Storage Calculations
Background
Pipe flow (conveyance) is generally modeled in HydroCAD by entering the appropriate shape and interior dimensions of the pipe. This allows HydroCAD to model virtually any pipe, regardless of design or manufacturer, without any special customization of the software. Details here.
Many pipe products can also be used for stormwater
storage, such as detention or retention applications. For pipe with a
smooth interior, the "Pipe Storage" option can be used to model the exact volume
based on the pipe shape and interior dimensions. However, certain types of
pipe, such as corrugated metal or plastic, may provide additional storage in the
corrugations, which is more difficult to model.
Certain installations may also use perforated pipe, with supplemental storage provided by the stone backfill. For these systems, the outside dimensions of the pipe must also be known, so that the stone displacement and storage can be properly calculated. For pipes with a smooth exterior (such as concrete), this can be handled by setting the appropriate wall thickness on the pipe storage screen. Again, pipes with a corrugated exterior present an additional challenge.
In order to provide optimum modeling for all types of pipe storage, HydroCAD includes chamber definitions for many common pipe products and sizes. Each chamber definition provides complete details for a specific type and size of pipe, including it's precise internal storage and exterior displacement. Each chamber definition also provides basic installation and layout parameters, allowing the automated layout of pipe storage systems using the HydroCAD chamber wizard.
Reinforced Concrete Pipe
HydroCAD provides a wide range of chamber definitions for modeling reinforced
concrete pipe (RCP), including round, elliptical, and arch
shapes. Each chamber definition specifies the inside dimensions of the pipe, plus the wall
thickness and displacement.
Concrete chamber definitions are also provided for common sizes of box pipe and crown-span (which is essentially a bottom-less box pipe). The cross-sections for each product can be viewed and compared on the chamber report screen, as show here.
The chamber library also includes a number of common sizes of concrete dry wells and galleys, plus several proprietary concrete products from CONTECH, Terre Hill, and PaveDrain.
Modeling Notes
When using chamber definitions in HydroCAD, the invert elevation
refers to the outside (bottom) of the pipe or chamber, rather than the inside.
This facilitates the placement of the chamber on a stone bed, and avoids the
need to make manual adjustments for the bottom thickness. HydroCAD will
automatically add the appropriate bottom thickness as required for each chamber
definition, so all you need to do is set the bottom elevation. And the
chamber wizard makes this even easier, because the chamber elevation is set
automatically based on the depth of the stone bed.
For further details read about chamber modeling and the HydroCAD chamber wizard.