“Press Forward” – Modern Steel Construction

Topics: Accelerated, Case Study, News, Prefabricated, Press Brake & Folded Plate

Excerpt and images provided by Modern Steel Construction – Press Forward: The durability and speed of tub girders made them the best choice to replace a concrete short-span bridge in Illinois.

A bridge project in small-town Illinois picked an emerging steel solution to replace a concrete bridge—and discovered its time-saving benefits along the way.

The choice to replace a four-lane bridge structure in Rock Falls, Ill., carrying Dixon Avenue (County Highway 5) over Howland Creek was press-break-formed tub girders (also known as press-brake tub girders or PBTG), a relatively new structure type that uses steel as the primary load-carrying component.

They lent themselves to minimized superstructure installation while also providing an ideal choice for longevity.

County Opts for Steel Over Concrete

The original bridge structure—located in Whiteside County, Ill.—over Howland Creek was built in 1954 and consisted of a three-span, 15-in.-thick reinforced concrete deck slab carrying two lanes of traffic.

In 1967, the existing structure was widened to accommodate four lanes. In 1983, the structure was rehabilitated with isolated patch repairs on the deck surface followed by deck scarification and the installation of a latex concrete overlay.

In the early 2000s, the concrete curbs and rail showed significant deterioration, and spalling was observed on the deck underside with exposure of reinforcement bars. The construction joint between the original structure and the widening structure had also deteriorated significantly.

When Whiteside County Highway Department officials weighed all considerations, they reduced their options to a precast-prestressed concrete (PPC) deck beam system or galvanized PBTG beams.

Ultimately, Whiteside County decided to install a PBTG for the projects.

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Additional Resources

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→