Hydraulic Design of Highway Culverts - DOT On-Line Publications

CHART 51A
Figure III-21--Inlet Control Curves - Circular or Elliptical Structural Plate
Corrugated Metal Conduits (SI Units)
D. Design Methods for Culverts without Standard Design Charts
Some culvert sizes, shapes, and materials do not have design nomographs and critical depth
charts. For example, long span, structural plate, corrugated metal conduits do not have
standard design charts. Developing design charts for all possible conduit shapes and sizes is
not practical because they are so numerous and new shapes are constantly being produced.
Also, the large size conduits tend to fall outside the nomograph scales. With some modification,
usual culvert hydraulic techniques can be used to analyze these culverts.
For outlet control, the analysis includes pressure flow and backwater calculations to determine
the headwater. Since the inlet has not been modeled, the inlet control equations are necessarily
based on hydraulic test results from similar tested conduit shapes. Appendix A contains
approximate inlet control equations for nonrectangular conduits with a variety of edge
conditions.
1. Inlet Control. In order to facilitate the design process, the appropriate inlet control
equations of Appendix A have been used to develop dimensionless inlet control design curves
for selected conduit shapes and edge configurations. The curves of Figures III-21 and III-22 are
for nonrectangular, structural plate corrugated metal conduits of two basic shapes and four inlet
edge conditions. Figure III-21 is for circular or elliptical conduits with the long horizontal axis at
the mid-point of the barrel. Figure III-22 is used for high and low profile structural plate arches.
Note that these figures are copies of Charts 51b and 52b and are for English Units. For SI
Units, see Chart 51a and 51b, respectively in Appendix D.
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