Turning a Challenge Into an Innovative Design Solution
Originally published by Associated Construction Publications
An innovative technology is being put to use by the West Virginia Division of Highways (WV DOH) to replace an old, structurally deficient bridge. The Fourteen Mile Bridge, along County Route 37 in Lincoln County, West Virginia, will be the first bridge in the state to utilize what is called a press-brake-formed steel tub girder bridge. This bridge system, a joint design effort between West Virginia University and Marshall University, uses galvanized shallow trapezoidal boxes fabricated from cold-bent structural steel plate. A concrete deck is precast on the girder, resulting in a unit that can be transported by truck to the project site.
Proponents of this type of design say it has the potential of becoming more economical than other short-span bridge designs – saving time and money since it takes less time to install, lasts longer, and requires minimal maintenance. The expedited installation process also helps to minimize disruption to traffic.
CR 37 is part of West Virginia’s Coal Resource Transportation System, which is intended to legally accommodate coal trucks weighing up to 120,000 pounds. Current average daily traffic count was 1,100 vehicles per day in 2018 and is projected to be approximately 1,250 vehicles per day in 2038. West Virginia Department of Transportation Communications Director Brent Walker relates the issues surround the old Fourteen Mile Bridge: “The previous structure consisted of a 42-foot span concrete channel beam superstructure founded on closed-faced cribbing abutments. The bridge was rated in poor condition and deemed structurally deficient per National Bridge Inventory standards. The bottom portion of the cribbing abutments had been encased in concrete in order to correct previous scour issues and deterioration. Due to its condition and load-carrying capacity, the bridge was last posted for a reduced weight restriction of 15 tons in 2016.”
WV DOH Joins with Two Universities, Short Span Steel Bridge Alliance on Project
Development of construction plans to replace the bridge began in October of 2016, with engineering, right-of-way, and construction phases all funded by a combination of state and federal dollars. WV DOH had supported research conducted by West Virginia University and Marshall University involving the use of press-brake-formed steel tub girders and their application and feasibility for use on short span bridges. WV DOH, the two universities, and the Short Span Steel Bridge Alliance worked together to develop the replacement project.
The Short Span Steel Bridge Alliance (SSSBA) is comprised of individuals from the transportation structures industry. Their organization focuses on bridges up to 140 feet in length and promotes new ideas, innovations, and concepts associated with the design and construction of short span steel bridges.”
Tracy Brown, West Virginia’s State Bridge Engineer, comments, “When the Fourteen Mile Bridge project came up, we felt it was an excellent location to utilize this type of bridge, which had never been built before in West Virginia, due to the localized geometry of the roadway and stream in addition to the type and volume of traffic that uses the highway. We were able to secure federal research money for the project due to the innovative nature of the press-brake-formed steel tub girders and the ultra-high performance concrete utilized in constructing the bridge.”
Via the design-bid-build process, the construction of the project was awarded to Orders Construction Company of Saint Albans, West Virginia, in March 2019. Orders Construction was founded in 1966 as a general contractor specializing in bridge construction. Initially working primarily on projects in West Virginia, the firm now delivers projects from the Mid-Atlantic to the Midwest. Construction commenced on August 20, 2019, with project completion expected by the end of 2019.
Bridge Design Based on Extensive Research
The Fourteen Mile Bridge project is being overseen by members of the SSSBA’s Bridge Technology Center, which include Karl Barth, Ph.D., the Jack H. Samples Distinguished Professor in the Statler College of Engineering and Mineral Resources at West Virginia University; and Greg Michaelson, Ph.D., P.E., Assistant Professor in the Weisberg Division of Engineering at Marshall University. Michaelson and Barth have conducted extensive research on the press-brake-formed steel tub girder system for the past several years; the focus of their work has been finding ways to make short-span steel bridge design more economical and efficient.
Michaelson comments, “Of the nation’s roughly 600,000 bridges more than 90 percent are short-span bridges that are less than 150 feet long. We envision the PBTG system as the future of short-span steel bridge design. West Virginia is the fifth state in the U.S. to implement this new system, along with Iowa, Ohio, Michigan, and Texas. ”
Process is Quicker Than Conventional Construction Methods
The new bridge consists of five press-brake-formed steel tub girders that span 58 feet from abutment to abutment. The tub girders are fabricated using normal structural steel plate and then cold-bending it to form a trapezoidal tub-shaped girder, with a bottom and two sides. The fabricated girders are hot-dip galvanized to help protect the steel from corrosion; then a reinforced concrete deck, utilizing ultra-high-performance concrete with a much higher strength than normal concrete, is precast on top of each individual girder.
Brown explains, “The girders are then transported to the project site and set into their final position on newly constructed concrete abutments. After all the beams have been set into place, 6-inch-wide concrete closure pours are made to connect the precast deck segments on top of each tub girder together. Once the concrete closure pours have had adequate time to set up, concrete barriers are installed along each edge of the bridge and the roadway approaches are graded and paved to meet up even with each end of the bridge. This is a relatively quick process when compared to conventional construction methods.”
On this project, a 12-inch diameter inspection access hatch was installed in the bottom portion of each individual girder to provide access for cameras for viewing the girder interiors during future bridge safety inspections. Says Brown, “The geometry of the bridge, with a 10-degree bridge skew and 8 percent maximum super-elevation, provided for an opportunity to stretch the boundaries for determining when this type of bridge could be used.
“These press-brake-formed tub girders can span up to 60 feet, which is the upper limit of the press brake machinery used to bend the steel plate. The maximum span could theoretically increase as the capability of press brake machinery increases.
“Other than the normal challenges involved with utilizing new materials and design concepts, in the form of ultra-high performance concrete and the press-brake-formed steel tub girders, there were no significant hurdles,” he continues. “The site characteristics and geometry – such as coal truck traffic, bridge skew, and roadway super-elevation – allowed us the opportunity to somewhat stretch the boundaries on the conditions of when and where these types of girders could possibly be used.”
More Press-Brake-Formed Steel Tub Girder Bridges Planned for State
In addition to providing a modern, structurally sound, and safe new bridge for CR 37 motorists, the Fourteen Mile Bridge project seems likely to spawn more use of its innovative design in West Virginia. A second press-brake-formed steel tub girder bridge project is expected to be constructed on U.S. Route 250 in Marion County in 2020.
“We believe that more press-brake-formed steel tub girder bridges will be built in West Virginia based on their modular design and efficient construction, which can result in less disruption to traffic,” says Brown. “We feel this type of construction will become increasingly competitive with the conventional construction methods from an economic standpoint as additional contractors become more comfortable with constructing them.”
For more information on how press-brake-formed tub girders can meet your bridge replacement needs, contact us for project assistance.
For suppliers of press brake tub girder, please see the Find-A-Supplier section.
Additional Links for the Fourteen Mile Bridge:
- New technology used to replace Lincoln County bridge; first project of its kind in West Virginia
- WVDOT uses new PBTG technology to build Fourteen Mile Bridge
- Bridge with breakthrough engineering design going up in West Virginia
- Bridge built with technology previously unused in West Virginia
- West Virginia Utilizes New Technology to Build Innovative, Cost-Effective Short Span Steel Bridge
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 in eSPAN140.
The press-brake-formed tub girder system is open source.
Dr. Barth and Dr. Michaelson will provide a presentation on press brake tub girders at the 2020 International Bridge Conference.
SSSBA Publishes New Research Report in Technical Series On Innovative Press-Brake Formed Steel Tub Girder Bridge Technology
Research report on field evaluation that includes skew and superelevation.
Seven volume research report on the development and testing of steel press brake formed tub girders.
An article highlighting press brake tub girders is published in a key bridge journal.
Buchanan County Iowa receives IBRC grant to constuct a press brake tub girder bridge.