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Arrow Innovations - High-Performance Steel Bridges

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High–performance steel combines strength with cost-effectiveness

High-performance steel (HPS) is structural steel plate that has the optimal balance of strength, weldability, toughness, ductility, and corrosion resistance to provide maximum performance in bridges while remaining cost-effective. HPS 70W, the most common HPS grade, is used primarily in girder anges, typically combined with conventional 50W to create a hybrid girder. HPS 50W is sometimes used in the webs to add higher toughness compared to conventional 50W, and HPS 100W is now available for applications that require an even higher strength.

Bridge performance depends on the following:

  • Weldability. High–quality welds are required for acceptable long–term performance of steel bridges. A weldability concern about the previously available 70W was the potential for hydrogen–induced cracking, also known as cold cracking or delayed cracking. The source of the hydrogen was typically moisture, but also included grease and other contaminants. Time–consuming and costly minimum preheat and interpass temperatures were used to control cracking during fabrication of 70W. The precision temperature control and handling required before, during, and after the 70W welding process added to time and cost.
  • Toughness. The steel's "toughness" denes its resistance to brittle fracture at low temperatures. The minimum requirements for steel toughness are based on the climate at the bridge location and whether the structure is fracture critical. A fracture critical bridge has at least one steel tension member that, if it failed, could cause part or all of the bridge to collapse. Fracture–critical bridges in the coldest climates require the highest minimum toughness.
  • Weathering. The need for repainting because of corrosion during the lifecycle of a bridge impacts the cost–eectiveness of the bridge installation.
1999 State Route 52 Bridge over Clear Fork River after construction: Tennessee's second HPS bridge consists of four welded plate–girder spans that rise 200 feet above the river in a wooded Tennessee recreational area. The optimized use of HPS 70W in the girders kept weights to a minimum.

HPS weldability benets include reduced welding process requirements, less susceptibility to hydrogen–induced cracking, and reduced fabrication costs. HPS can be welded under a variety of conditions without requiring excessive process controls that increase time and cost. HPS 70W plates up to 2.5 inches thick can be welded with limited preheat requirements. HPS toughness is signicantly higher than the minimum specication requirements for toughness of bridge steels, largely because of the lower carbon and sulfur levels of HPS. This higher toughness means structural members are more resistant to fatigue and fracture. The higher crack tolerance increases available time for detecting and repairing fatigue cracks before a bridge becomes unsafe.

2006 RIDOT Providence River Bridge during construction. The superstructure main span, with HPS–70W tub girders in the negative moment area and HPS–50W ties in the skewed network arch, is moved with self–propelled modular transporters (SPMTs) from the staging area, where it was assembled, onto barges to be floated to the bridge site. The SPMTs support the span at two locations along its length, approximately at the quarter points to allow room for erection onto the final supports. Temporary bracing stiffens the arches at the temporary support locations. The deck will be constructed after the span is erected.

The higher strengths available in HPS also allow the design of more efficient superstructures. Plate and box girders optimized by using a hybrid combination of high–strength HPS in the flanges and conventional steel in other regions provide a lower first cost and are expected to have a lower life–cycle cost. The number of girders per span can be decreased, reducing weight of the superstructure as well as the costs of design, detailing, fabrication, erection, and inspection. Girders can be shallower, increasing vertical clearance underneath a bridge replacement without a substantial change to the bridge's profile or approaches. Span lengths may be increased, reducing the number of piers on land or in water.

The weathering characteristics of HPS provide high corrosion resistance without painting or with limited painting. This reduces life–cycle cost by minimizing maintenance painting operations required during the life of a bridge that is painted or otherwise coated.

HPS has been used in a number of bridge projects across the country:

  • In 1997, the first HPS bridge was built in Dodge County, NE. The Snyder South Bridge on State Route 79 is a 150–foot (ft) long single–span plate–girder bridge for which the originally designed 50W was replaced with HPS 70W to gain experience in the HPS fabrication process.
  • In 1998, a second HPS bridge, in Jackson County, TN, opened to traffic. The State Route 53 Bridge over Martin Creek has two 236–ft long 50W continuous plate–girder spans that were redesigned to optimize HPS 70W in the girders. The superstructure weight was reduced about 25 percent at a cost savings of 10 percent.
  • Since the late 1990s, more than 250 bridges with HPS components have been opened to traffic, and at least another 150 are in design or under construction. Forty–five states have HPS bridges in various stages of completion.

For More Information

Contact

Krishna Verma
Senior Bridge Engineer
Office of Infrastructure
FHWA
202–366–4601
krishna.verma@dot.gov

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Events

Contact

Brian Kozy
Office of Bridges and Structures
202-493-0341
brian.kozy@dot.gov

Updated: 04/04/2011
 

FHWA
United States Department of Transportation - Federal Highway Administration