The National Academies

NCHRP IDEA 20-30/IDEA 162 [Completed (IDEA)]

Full-Scale Prototype Testing and Manufacturing and Installation Plans for New Scour-Vortex-Prevention scAUR and VorGAUR Products for a Representative Scour-Critical Bridge
[ NCHRP 20-30 (NCHRP-IDEA) ]

  Project Data
Funds: $140,000
Staff Responsibility: Inam Jawed
Research Agency: Applied University Research, Inc.
Principal Investigator: Roger L. Simpson
Completion Date: 12/14/2013
Fiscal Year: 2012

This project tested and developed manufacturing and installation plans for scAURTM and VorGAURTM products for scour-critical bridges to demonstrate their effectiveness in preventing scour-causing vortical flow characteristics at piers and abutments. Plans were developed and refined for the manufacture and installation of full-scale scAURTM and VorGAURTM products on at least one pier and one abutment of a selected scour-critical bridge in Virginia that has a record of flooding and is representative of scour-critical bridges across the US. The merits of five candidate Virginia bridges were considered in detail and a bridge was selected by Applied University Research (AUR) and recommended to Virginia DOT. Reynolds number and bridge pier and abutment size effects were examined using computations for a full-scale pier and show that scAURTM with VorGAURTM is effective in preventing scour-causing vortical flow at both model and full scale. The flow physics shows that full-scale piers and abutments have lower pressure gradients and turbulent stresses than at model scale, so if scour is prevented at model scale, it will be prevented at full scale. Data on the performance of these products with several smaller size sediments at model scale were obtained in the AUR flume. Data from published sources suggested that model scale tests be conducted for b/d50 > 50, where b/d50 is the ratio of pier width to median sediment grain diameter. The researchers used values of 38.1 < b/d50 < 64.6. During flume tests, no scour was observed around the scAURTM with VorGAURTM model for any gravel in this range within the gravel level y/b = +/- 0.004 measurement uncertainty. The performance of scAURTM and VorGAURTM concepts for a larger class of abutments was examined in model scale AUR flume tests. Spill-through and wing-wall abutment flume models, with and without scAURTM and VorGAURTM product features, were tested and show that scAURTM and VorGAURTM product features prevent scour for wing-wall abutments and spill through abutments. The effects of contraction scour, long-term degradation scour, settlement and differential settlement of footers, undermining of the concrete scAURTM segments, and variable surrounding bed levels were also examined. An additional fairing surface in the front prevents undermining of the foundation for piers and abutments and has been tested in the AUR flume. A full-scale scAURTM and VorGAURTM pier model was constructed and tested under various conditions in the large flume at the Iowa Institute for Hydraulic Research during May 2013, with results that were comparable to results for 1/7 size models in the AUR flume. Manufacturing methods and installation processes for scAURTM and VorGAURTM products were refined and complete plans and cost estimates for manufacturing full-scale scAURTM and VorGAURTM products were developed. An attractive cost-effective manufacturing alternative for a scAURTM retrofit bridge pier or abutment fairing is to use stainless steel (SS) or even weathering steel, rather than shotcrete or precast concrete. Its corrosion resistance gives it a lifetime of 100 years even in seawater environments, using a proper thickness, construction methods, and type of SS. In the case with new construction, essentially the difference between the way cast-in-place bridge piers and abutments are constructed currently without the scAURTM products and in the future with the scAURTM products is that scAURTM fairing steel forms are used for the concrete. Clearly, since the new construction cost is about 1/3 of retrofit costs, the best time to include the scAURTM fairing on piers or abutments is during new construction. The present value cost of these products over the life of a bridge is an order of magnitude cheaper than current scour countermeasures. The final report provides all relevant data along with plans for implementation of the scAURTM and VorGAURTM products by highway agencies.

The contractor's final report is available.

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