Steel Tub Girder Research Underway to Evaluate Compactness Designation of Skewed Box Sections

Topics: Innovation, Press Brake & Folded Plate, Research

Photo Credit: Dr. Karl Barth, West Virginia University

Four fabricated skewed press-brake steel tub girders (PBTGs – pictured above) donated by SSAB Americas and fabricated by Valmont Structures have arrived at West Virginia University for lab testing in a research project expected to provide a more efficient design of welded and press-brake steel tub girder bridges in skewed applications.

Current AASHTO provisions for box girders are too restrictive for tub girders with skewed supports. A more efficient design will lower the initial cost of tub girder bridges to make them more competitive with concrete bridges.

Brook WoldegabrielGraduate Research Assistant West Virginia University

Brook Woldegabriel, Graduate Research Assistant at West Virginia University, presented research findings to the SSSBA Technical Standards Council (January 23, 2023) on “Improved Load Distribution Factors for Shallow Steel Tub Girders.”

The Short Span Steel Bridge Alliance’s Bridge Technology Center is developing a technical report detailing a finite element study conducted on skewed steel tub girders. The objective is to assess flexural behavior, compare it to AASHTO LRFD models, and then assess the validity of a noncompact designation for skewed tub girders.

It is anticipated that this effort may produce code revisions in both AASHTO Chapter 4 and AASHTO Chapter 6. This will include modified strength provisions and modified provisions for live load distribution.

The final report will be available in 2024.

In the video below, Dr. Karl Barth, West Virginia University, presents information on the development of press-brake formed tub girders for short span bridges.

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

What are Press Brake Tub Girders?

Press-brake-formed tub girder (PBTG) is a new technology for short span bridge applications. It consists of modular galvanized shallow trapezoidal boxes fabricated from cold-bent structural steel plate (watch fabrication video). A concrete deck is recommended to be precast on the girder and the modular unit can be shipped by truck to the bridge site.

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 are available to use in the free-to-use, web-based design tool eSPAN140.

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

Learn more about press brake tub girders→