PennDOT Uses Corrosion-Resistant Steel for Flex Beam Pilot Bridge Project

With more than 25,000 state-owned bridges, Pennsylvania has the third-largest number of structures in the nation. The average age of bridges in the state system is over 50 years old. The Pennsylvania Department of Transportation (PennDOT) is committed to maintaining, improving and extending the service lives of their bridges, thus deferring the need for major rehabilitation and saving future costs.

Recently, PennDOT’s District 1-0 implemented an innovative design to extend the service life for a new bridge currently being installed. The concept uses a Flex Beam bridge system combined with corrosion-resistant A709-50CR steel. PennDOT claims the project will validate a low-cost system for rapid replacement of deficient short-span highway bridges.

3-D CADD renderings were provided to illustrate rebar layout and detailing for the Flex Beam bridge system.

What is a Flex Beam Bridge?

According to PennDOT, the Flex Beam bridge system uses modular, lightweight, full-span components prefabricated from a steel section and concrete deck. The Flex Beam “panel” is constructed in a fabrication shop and transported to the bridge location. The bridge uses a composite construction design through steel stringer and a reinforced deck interface.

These components can be rapidly installed by small teams using light construction equipment. This bridge concept was created through collaboration between Lehigh University and PennDOT engineers.

Learn more about Flex Beam bridges in this presentation from PennDOT.

PennDOT’s Erie County SR 3010 over the West Branch of Cussewago Creek Bridge features the use of A709-50CR steel.

Pilot Project Features A709-50CR Corrosion-Resistant Steel

The bridge was completed in August 2021 in PennDOT’s District 1-0, replacing a 65-year-old bridge (built in 1956) with a 32-foot-span Flex Beam bridge. The new bridge, Erie County SR 3010 over the West Branch of Cussewago Creek, features the use of A709-50CR steel. This high-chromium corrosion-resistant steel is proven to perform extremely well in corrosive environments. A709-50CR steel includes a range of 10.5 percent to 12.5 percent chromium, which greatly enhances the corrosion resistance of this type of steel in comparison to conventional steels widely used for structural applications.

Closure pours on the modular units were completed with ultra-high-performance concrete (UHPC).

Ohio Structures fabricated the beams for the structure and PennStress precast the deck. DS Brown fabricated the bearings and sole plates. PennDOT is installing the bridge with a Department-let contract and Contractor forces. The existing abutments were re-used to set the new bridge, and closure pours on the modular units will be completed with ultra-high-performance concrete (UHPC).

View the project plans.

The existing abutments were re-used to set the new bridge, and closure pours on the modular units were completed with ultra-high-performance concrete (UHPC).

By using A709-50CR steel, PennDOT expects to achieve a longer service life with minimal maintenance required for the bridge. It will be tested to assess service load performance. Details will be developed for the field-installed connections between components.

The Future of Flex Beam in Pennsylvania

Based on the outcome of this project, PennDOT plans to use Flex Beam with A709-50CR steel in future projects. PennDOT has issued design standards for this concept in 10-foot increments in span length (30-70 feet), 4-foot increments in roadway width (24-40 feet), and girder spacing of 36 and 40 inches.

The SSSBA would like to acknowledge PennDOT representatives Mark Nicholson, Thomas Macioce and Kristin Langer for their assistance with developing this article.

Additional Information

The North Carolina Department of Transportation is requesting proposals for Transportation Pooled Fund Study TPF-5(493), “Investigation of Dual Grade/Hybrid Steel Plate Girders Utilizing Stainless Steel.” The objective of this research is to examine the feasibility of connecting bridge-construction approved ASTM stainless steel (currently only Grade 50CR is approved) to conventional steel (Grade 36, 50, 50W, etc.) through welding or bolting and to develop guidelines to assist designers and fabricators when connecting stainless steel plates to conventional steel plates in the superstructure of highway bridges. The guidelines would be considered a supplemental document to the AASHTO LRFD Bridge Design Specifications and the AASHTO LRFD Bridge Construction Specifications. For more information or to submit a proposal, please refer to the Connect NCDOT website.