Mary Lou Ralls, Texas Department of Transportation and Benjamin Tang, Federal Highway Administration
Transportation agencies today face significant challenges to restore highway capacity while enhancing safety through construction work zones. About one-third of our Nation’s bridges are in need of repair or replacement. During the summer road work season, 20 percent of the National Highway System is typically under construction. This translates into 6,400 highway work zones with a corresponding loss of 6,200 lane-miles (10,000 lane-km) in capacity. On a road construction project with a high volume of traffic, the cost of traffic control can be 30 to 50 percent of the construction cost. These costs can be reduced and work zone safety enhanced through the use of accelerated construction methods.
Limited available funding and significant construction needs have resulted in initial cost controlling bridge design and construction. In addition to managing costs, owners are now responding to the need to “get in, get out, and stay out” as the advancing age of our highway infrastructure necessitates increased reconstruction. Prefabricated bridge elements and systems, in combination with HPC and accelerated construction requirements in the contracts, help meet the need for rapid bridge construction.
For example, the Virginia Department of Transportation recently replaced the superstructure of its I-95 James River Bridge without closing a single lane to rush hour traffic. Prefabricated superstructure segments with low permeability lightweight concrete decks and accelerated construction requirements were used to accomplish this feat. With 110,000 vehicles per day, the James River Bridge was reconstructed Monday through Thursday nights only from 7 p.m. to 6 a.m., with disincentives that could reach $250,000 a day for failure to open all lanes to traffic. Throughout the nighttime construction, half the structure remained open to carry traffic. The superstructure replacement was completed with partial closures on 167 nights. Conventional construction methods would have required total closure for three years.
As bridge owners strive to meet the challenges of reconstructing the nation’s aging highway structures while accommodating traffic, the American Association of State Highway and Transportation Officials (AASHTO) and the Federal Highway Administration (FHWA) have teamed together to implement prefabrication nationwide.
AASHTO, through its Technology Implementation Group (TIG) panel, has been working to implement prefabrication since 2001. The panel’s mission is to extend the use of prefabricated elements and systems in bridge design and construction by increasing awareness of and confidence in innovative prefabrication, and by further development and refinement of this technology. The panel has sponsored sessions and workshops; authored articles and papers; facilitated research; and published a brochure, an interactive CD-ROM, and a website featuring projects that used various types of innovative prefabrication.
The AASHTO TIG panel is now mainstreaming its activities prior to being disbanded in 2005. Together with the FHWA, AASHTO will continue its development and refinement of prefabricated systems through its Highway Subcommittee on Bridges and Structures. Working with AASHTO, the FHWA will provide the leadership role in technology transfer of innovative prefabrication. Ongoing AASHTO/FHWA activities include:
- Transfer of the AASHTO TIG prefabricated bridges web site content to the FHWA Accelerated Bridge Construction Technologies web site with a link for future access.
- Presentations on the findings from this spring’s international scanning tour.
- Publication of a second brochure this summer.
- A national workshop to be held September 8-10, 2004, in New Brunswick, New Jersey
The FHWA has been an active partner with AASHTO in the prefabricated bridges initiative from its beginning. The FHWA has sponsored and co-sponsored workshops and presented many project case studies on the use of both HPC
and prefabricated bridge systems. Together with the industry partners, the FHWA has developed a new paradigm for constructing bridges over a relatively short time such as overnight project delivery.
In addition to the prefabrication initiative, the FHWA is undertaking a two-pronged process to help states deploy accelerated construction technology. The process involves deploying a team of highly experienced technical experts in numerous disciplines who work with the state owners to scope the project from conception through construction. The process aims at collapsing the time-frames in various tasks before traffic flow is interrupted. The second part of the process is to focus on the bridge construction activity in the critical path. By using prefabricated bridge elements and systems to quickly erect structures, work can be completed in a shorter time-frame. The FHWA is compiling case studies that used different elements and systems and will share the gained knowledge with the community through various workshops in the near future.
High performance concrete (HPC) facilitates the use of prefabrication in design, construction, and long-term performance.* HPC offers the following advantages that are useful in prefabricated bridge elements and systems:
- High early strength concrete facilitates form removal and, therefore, can speed production (“get in”).
- High strength concrete can be used in design to reduce the number of required beams or their size and, therefore, reduce hauling and lifting weights (“get out”).
- Supplementary cementitious materials improve durability for a longer service life of prefabricated systems (“stay out”).
The combination of prefabrication, HPC, and accelerated construction requirements in contracts helps the FHWA and AASHTO meet today’s bridge construction challenges.
Web Sites
For further information, see the following web sites:
AASHTO: www.aashtotig.org/focus_technologies/prefab_elements/
FHWA: www.fhwa.dot.gov/bridge/prefab/index.htm
*See HPC Bridge Views Issue No. 21 May/June 2002.