Documentation and Evaluation of ASTM A709 Grade 50CR Steel Bridges on Virginia’s Eastern Shore

About the report:

Corrosion is a common deterioration mechanism leading to costly maintenance of steel bridges.  Although this is the case all over Virginia, it is especially true on Virginia’s Eastern Shore, a 70-mile-long peninsula located between the Atlantic Ocean and Chesapeake Bay saltwater bodies.  This was especially evident by corrosion damage and the subsequent need for replacement of the Holdens Creek Bridge and repairs on the Onancock Bridge on the Eastern Shore.  ASTM A709 Grade 50CR (50CR) steel, a utility grade stainless steel, was selected for the replacement girders of the Holdens Creek Bridge and the bolted repairs of the Onancock Bridge.  Since 50CR steel has a greater initial cost compared to traditional corrosion protection systems, design alterations were implemented to reduce the initial cost.

The purpose of this study was to document and evaluate both Eastern Shore bridges, including the condition of each bridge prior to replacement/repair, the design processes with cost-saving alterations, and the condition of each bridge after replacement/repair.  Cost-saving design alterations included limiting the amount of 50CR steel used, limiting the number of 50CR steel plate thicknesses, using simpler weld details, using galvanized secondary members, and using galvanized fastener assemblies.  For the Holdens Creek Bridge, nonstructural galvanized and metallized/sealed beams were added to the bridge, and for the Onancock Bridge, uncoated weathering steel repairs were implemented, both of which were done to allow for a long-term corrosion performance comparison.  A cost analysis was also conducted to determine the future economic potential of 50CR steel.  This included examining the recent macroeconomic environment and legislation for highway construction, alloy composition and supply of alloys for 50CR steel, and macroeconomic trends in U.S. steel production that affect the near-future supply of 50CR steel.

Inspection of the Holdens Creek Bridge 1 year after replacement showed that the 50CR steel girders and nonstructural galvanized and metallized/sealed beams were performing well.  Inspection of the Onancock Bridge 5 years after repair showed some zinc product migrating between the galvanized fastener assemblies and 50CR steel repair plates.  The uncoated weathering steel repairs were not exhibiting pitting or laminar corrosion but did exhibit some loosely adherent small flakes.  Both bridges will be monitored over time.  The cost analysis showed that the unit cost of 50CR steel for bridge girders on Virginia Department of Transportation (VDOT) projects decreased from $5.84/lb in 2015 to $3.10/lb in 2020, a 47% decrease, an achievement of economic significance.  This cost falls in line with prices VDOT has paid for other bridge repairs in recent years.  The macroeconomic environment of the last 3 years has been unprecedented and has caused costs for transportation agencies to spike by 50%; however, data suggest that U.S. steel markets are recovering.  Alloys in 50CR steel except nickel have also showed marked price and supply stability over this period.

The study recommends that VDOT continue to investigate corrosion-resistant steels, such as 50CR steel, to provide a long service life for steel bridges in corrosive environments.  Further, VDOT should update its 50CR steel design guidelines to incorporate the cost-saving design alterations discussed in this report.  Finally, VDOT should improve its specifications for metallized steel for potential expanded use in corrosive environments.

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Supplemental files can be found at: https://library.vdot.virginia.gov/vtrc/supplements

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