History and Overview of Press Brake Tub Girders

The press-brake-formed tub girder is a recently developed technology for short span bridge applications. In 2009, the Federal Highway Administration (FHWA) challenged the North American steel industry to “develop a cost-effective short span steel bridge with modular components which could be placed into the mainstream and meet the needs of today’s bridge owners, including Accelerated Bridge Construction (ABC).”

The Short Span Steel Bridge Alliance (SSSBA) organized the Modular Steel Bridge Task Group—consisting of 30 organizations representing the SSSBA, Steel Market Development Institute, National Steel Bridge Alliance, National Association of County Engineers, steel bridge fabricators, university faculty members, steel manufacturers, government organizations, and bridge owners–to develop ideas to meet this challenge. Led by Karl Barth, Ph.D., P.E., Samples Professor of Civil and Environmental Engineering at West Virginia University, the group decided in October 2011 that a shallow steel press-brake tub girder technology provided the best opportunity to meet the FHWA goals for economic value, innovation, and ABC practices. A preliminary specimen design was developed for spans up to 60 feet. The idea went from concept to reality in just three years, a significant accomplishment.

The Short Span Steel Bridge Alliance developed standardized plans using standard plate sizes (60”, 72” 84”, 96”, 108”, 120”). The designs were developed to achieve maximum structural capacity.

Three years of testing then commenced at West Virginia University on eight press-brake tub girder specimens donated by Nucor Corporation, SSAB Americas, United States Steel Corporation, and EVRAZ North America. The specimens were cold-bent to specific dimensions and then tested in three-point bending loading scenarios under both static and cyclic loading in the Major Structures Lab at West Virginia University. Initial testing was completed in 2014. Additional testing was completed in 2016.

In the meantime, Buchanan County (Iowa) Engineer Brian Keierleber, P.E., submitted a proposal to replace the Amish Sawmill Bridge at 1358 Dillon Avenue in Fairbank, Iowa with funding from the FHWA’s Innovative Bridge Research and Deployment (IBRD) Program. The $350,000 grant was awarded on the basis of using a trapezoidal bent steel girder section supported on Geosynthetic Reinforced Soil (GRS).

Construction on the Amish Sawmill Bridge began in late summer 2015 and was completed in December 2015. The deck for this project was cast-in-place, rather than using modular pre-cast deck units, which added to the time of construction. The bridge was dedicated on January 8, 2016 with a ribbon-cutting ceremony featuring several government and transportation officials.

Description

The press-brake-formed tub girder system consists of modular galvanized shallow trapezoidal boxes fabricated from cold-bent structural steel plate. The concrete deck is recommended to be precast on the girder and the modular unit can be shipped by truck to the bridge site.

The press-brake-formed tub girder system consists of modular galvanized shallow trapezoidal boxes fabricated from cold-bent structural steel plate.

The system utilizes standard plate widths (based on availability) and is optimized to achieve maximum structural capacity, with most of the steel in the bottom flange and increased torsional stiffness. It is a closed system, since the girder is closed at the bottom. It is versatile for multiple-deck options.

The system utilizes Accelerated Bridge Construction practices, since it:

• Can be installed in one or two days
• Is modular, allowing the use of a precast deck
• Is cost-effective―as much as 1/3 less than a standard concrete girder structure
• Is simple to fabricate, requiring very little welding.

The Short Span Steel Bridge Alliance has developed standardized plans using standard plate sizes (60”, 72” 84”, 96”, 108”, 120”). The designs were developed to achieve maximum structural capacity and can be accessed within eSPAN140.

The press-brake-formed tub girder system is open source.

Application

Press-brake-formed tub girders are versatile for multiple-deck options. They can be used for both tangent and skewed configurations, as well as simple and continuous spans. They are recommended for single spans up to 60 feet or less. Spans may be spliced together to form a multi-span bridge greater than 60 feet.

Testing for the press brake tub girder was completed at West Virginia University.

Constructability

The stable modular nature of the pre-topped tub girders allow for accelerated on-site construction. There is a reduction in additional details such as stiffeners and cross frames. The concrete deck is precast on the girder and the modular unit can be shipped by truck to the bridge site.

The inside of a press-brake tub girder. Inspection holes can be fabricated on the bottom of the girder to allow visual inspection.

Evaluation

The press-brake-formed tub girder system offers significant cost savings, ease in shipment and fabrication, accelerated construction and design versatility, with the potential to replace thousands of short span bridges over the next decade. Some states have already installed press-brake-formed tub girder bridges including:

• Alabama
• California
• Iowa
• Illinois
• Indiana
• Louisiana
• Michigan
• Minnesota
• Missouri
• Nebraska
• New Mexico
• Ohio
• Oklahoma
• Oregon
• Pennsylvania
• Tennessee
• Texas
• West Virginia

For More Information:

Karl E. Barth, Ph.D.
Co-Leader, SSSBA Bridge Technology Center
Jack H. Samples Distinguished Professor at West Virginia University
Email: Karl.Barth@mail.wvu.edu

Gregory K. Michaelson, Ph.D., P.E.
Co-Leader, SSSBA Bridge Technology Center
Assistant Professor, Department of Civil Engineering at Marshall University
Email: michaelson@marshall.edu

Read more in Engineering News-Record.

Read more in STRUCTURE Magazine.

Read more in Modern Steel Construction.