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Assessment of HY-8 and HECRAS Bridge Models for Large-Span Water-Encapsulating Structures

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  • Creators:
  • Corporate Creators:
    Purdue University. Joint Transportation Research Program
  • Corporate Contributors:
  • Subject/TRT Terms:
  • Publication/ Report Number:
    FHWA/IN/JTRP-2018/14
  • DOI:
  • Resource Type:
    Tech Report
  • Geographical Coverage:
    United States;Indiana
  • Edition:
    Final Report
  • Corporate Publisher:
    Purdue University. Joint Transportation Research Program
  • Abstract:
    Current INDOT policy requires that culvert-like structures with spans greater than 20 ft be treated for purposes of hydraulic analysis as a bridge, and hence mandates the use of software such as HEC-RAS for predicting the headwater, rather than the culvert-specific software, HY-8. In this context, culvert-like structures are assumed to have a standard inlet geometry (e.g., such as those already modeled in HY-8) and a constant barrel geometry. The present study examines the technical basis of this policy, and whether the policy could be revised to allow the application of simpler culvert-hydraulics analysis and HY-8 to culvert-like structures with spans greater than 20 ft. Laboratory experiments were performed with model box culverts of span 1.5 ft and two streamwise lengths, 2.1 ft and 8 ft, and performance curves describing the variation of headwater with discharge were obtained. The effects of bed roughness, the presence or absence of a cover (if present, the rise was 0.5 ft), and a range of tailwater levels, were investigated. The laboratory observations were compared with predictions by HY-8 and HEC-RAS models, and the model performance assessed. In general, HY-8 predictions were found to be as good as, and in some cases superior to, the HEC-RAS predictions, for both long and short culvert-like structures. This was attributed to the empirical information in HY-8 being more tailored to the specific standardized geometry of culvert-like structures, and the automatic inclusion of roughness effects, whereas HEC-RAS, at least when used with default coefficients and settings, relied on generic coefficients and neglected roughness effects. It was therefore recommended that a change in INDOT policy allowing large-span culvert-like structures to be analyzed using conventional culvert hydraulics would be technically justified for problems where the structure could be considered in isolation and accurate input data are available.
  • Content Notes:
    Lyn, D. A., Dey, S., Saksena, S., & Merwade, V. (2018). Assessment of HY-8 and HEC-RAS bridge models for large-span water-encapsulating structures (Joint Transportation Research Program Publication No. FHWA/IN/JTRP-2018/14). West Lafayette, IN: Purdue University. https://doi.org/10.5703/1288284316781
  • Format:
    PDF
  • Funding:
    SPR-3815
  • Collection(s):
  • Main Document Checksum:
    urn:sha-512:90c9645187fe9f91e49f7675b455557b66ae0a7e2717bd95249fd9eb5fdd21bee56c8e26e33cd5d08edc2086747ba851386addb7fae1fbfea30bb3d15a9b44de
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  • File Type:
    Filetype[PDF - 10.00 MB ]
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