A civil engineering professor from West Virginia University and one of his former students, who is now on the faculty at Marshall University, have teamed up to create a cost-effective bridge construction system for short-span steel bridges.
Karl Barth, Samples Professor of Civil and Environmental Engineering at West Virginia University, and his former doctoral student, Greg Michaelson, now an assistant professor in the Weisberg Division of Engineering at Marshall University, have introduced a new type of tub girder that requires less fabrication and installation time than conventional bridge systems. The duo are working in conjunction with the Short Span Steel Bridge Alliance.
According to Barth, the technical working group, which is made up of more than 30 partners from the steel industry, academia, government organizations and bridge owners, took the the pressed-brake-formed tub girder system from idea to reality within three years.
“The Federal Highways Administration issued a challenge to us in 2009 to develop a cost-effective accelerated bridge construction system for steel bridges 140 feet or less,” Barth said. “This led to the development of an online tool, eSPAN140, which has been successfully employed for a number conventional bridge designs. We also explored a variety of concepts for accelerated bridge construction and settled on the tub girder system because it requires none of the expensive fabrication of traditional systems and uses less material.”
The system uses modular galvanized trapezoidal boxes fabricated from cold-bent structural-steel plates that can be constructed using either galvanized or weathering steel. The concrete deck is precast on the girder and the modular unit is shipped by truck to the bridge site.
The system offers several advantages over traditional short span steel bridge solutions.
“The girder itself, which is available from the steel mill in standard plate thicknesses and widths, is simple to fabricate, requiring very little welding ― one girder can be produced in 45 minutes,” Barth said. “Because of the system’s modular composite design, there is a reduced need for additional details such as stiffeners or cross-frames. Due to its modular nature, the composite unit can be easily shipped to the bridge site, allowing for accelerated construction and reduced traffic interruptions.”
One of the challenges the research team faced before initial testing could be conducted was that they had to develop preliminary girder capacity predictions and evaluate potential efficiencies for a variety of potential configurations.
“This took some time before we were able to arrive at our final recommended designs and test specimen configurations,” Barth noted.
The experimental testing was conducted at WVU. Michaelson continues to collaborate on these efforts, assisting with data analysis, modeling and field-testing efforts.“The most satisfying aspect of the project is the reception from the industry,” said Michaelson, who earned his master’s and doctoral degrees in civil engineering from WVU in 2010 and 2014, respectively.
“It’s exciting to see all the interest in the system from owners, fabricators and engineers. One of the key strengths of the system is its ability to be standardized. We have a lot of work ahead of us, but the system has remarkable advantages in mass applications.”
According to the SSSBA, the system offers as much as a 50 percent reduction in fabrication costs, compared to proprietary cold-formed box-girder systems.
A grant from the FHWA’s innovative bridge research program funded the first PBTG bridge in Buchanan County, Iowa; it was completed in January. The bridge is providing valuable data to the research team, which is conducting additional testing to measure performance and identify further efficiencies that can be realized for future designs.
Barth noted that three additional bridges are planned for 2017, with two scheduled for West Virginia, in Monongalia and Wayne counties, and one in Ohio in Muskingum County.
“There are others on the horizon as well,” Barth said. “We have also had discussions regarding deploying this system in both Canada and Mexico.”