Scour at Contracted Bridges

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Scour at Contracted Bridges

Author: Wagner, Chad R | Size: 7.27 MB | Format: PDF | Quality: Original preprint | Publisher: Transportation Research Board | Year: 2006 | pages: 299 | ISBN: -

The main purpose of National Cooperative Highway Research Program (NCHRP) Project 24-14 was to collect field data from which processes affecting scour magnitude in contracted bridge openings could be identified, to support verification of physical and numerical model studies, and to improve guidelines for applying scour-prediction methods at contracted bridge sites. The objectives were accomplished by the collection and analysis of data at 15 bridge sites. A combination of real-time and post-flood data collection activities provided comprehensive field data sets. Detailed directional velocity data were collected throughout the reaches affected by the bridge where flood and site conditions permitted (4 of 15 sites). In addition, streambed, stream bank and floodplain material properties were described. Raw data were reduced and assembled into a database accessible through the World Wide Web (http://ky.water.usgs.gov/Bridge_Scour/BSDMS/index.htm). Scour predictions based on the methods provided in HEC-18 were compared to the observed scour at each site. Flow velocity and depth data obtained from real-time investigations along with post-flood topographic surveys were used to develop and calibrate two-dimensional hydraulic models (RMA-2 and FESWMS) at two sites. One-dimensional hydraulic models (HEC-RAS or WSPRO) were developed for all sites where sufficient cross sectional data were collected or available. The velocities obtained from numerical simulations were compared to measured velocities. The observations and measured data demonstrate the inaccuracies of the current scour prediction methods as specified in HEC-18 related to contraction scour and abutment and the effectiveness of the Melville and Dongol method for predicting scour at a pier with debris. Measured flow-velocity distributions and those computed from the one-dimensional and two-dimensional models were compared. Scour topography computed with the two-dimensional hydraulic model and two-dimensional sediment-transport model were compared. Recommendations for future research that will advance scour-prediction methods were provided, including suggested modifications to the Strategic Plan for Scour Research (NCHRP Project 24-8). Appendix A contains 10 case studies.

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