HY8:South Dakota Concrete Box

HY-8 Version 7.3 and later has coefficients for computing inlet control depths using research contained in FHWA Publication No. FHWA-HRT-06-138, October 2006: Effects of Inlet Geometry on Hydraulic Performance of Box Culverts.

The South Dakota Concrete Box is a traditional Concrete Box that uses coefficients determined by the TFHRC hydraulics lab and the South Dakota DOT (SDDOT). This shape-type also opens up additional inlet edge types. The South Dakota Concrete Box shape-type was added to HY-8 to allow the user to continue to use traditional coefficients but also to be able to choose to use new coefficients.

Overview and implementation

The document "Effects of Inlet Geometry on Hydraulic Performance of Box Culverts" (FHWA Publication No. FHWA-HRT-06-138, October 2006) describes a series of tests that were performed to obtain design coefficients for various inlet configurations on reinforced concrete box culverts. The following variations in inlet configurations were tested: wingwall and top edge bevels and corner fillets, multiple barrels, different culvert span-to-rise ratios, and skewed headwalls. The results of the tests were K, M, c, and Y inlet control design coefficients and 5th-degree polynomial coefficients (required by HY-8) that were given in the FHWA document. The 5th-degree polynomial coefficients given in the FHWA document cannot be used directly in HY-8 because the coefficients were only developed for a HW/D range between 0.5 and 2.0. HY-8 requires the polynomial coefficients to be valid between HW/D values of 0.5 and 3.0. Therefore, the polynomial coefficients had to be re-computed using the K, M, c, and Y coefficients from the FHWA report.

Several recommendations were made at the end of the FHWA document. Since the recommendations were a consolidation of the FHWA research, these recommendations were used in HY-8. The recommendations consolidated the results of the South Dakota box culvert testing into 13 different sets of coefficients, called "Sketches", which represent different inlet conditions. The HY-8 developers further consolidated the results into 10 sets of inlet configurations that were added as a "South Dakota Concrete Box Culvert" type in HY-8.

For information on the exact coefficients used and to view diagrams showing the different culvert configurations that were implemented in HY-8, see the help describing the HY-8 South Dakota Concrete Box polynomial coefficients.