Accelerated Bridge Construction
FHWA –Every Day Counts Initiative
With over a quarter of the nation’s bridges requiring rehabilitation, repair or replacement and decreasing funds to address these needs, the Federal Highway Administration (FHWA) was faced with the challenge of doing more with less. In 2009, FHWA launched the Every Day Counts (EDC) initiative, in cooperation with the American Association of State and Highway and Transportation Officials (AASHTO), to speed up the delivery of highway and bridge projects and to address limited budgets. EDC is a state-based model to identify and rapidly deploy proven but underutilized innovations to shorten the project delivery process, enhance roadway safety, reduce congestion and improve environmental sustainability.
Accelerated Bridge Construction
Accelerated Bridge Construction (ABC) is a construction methodology that was developed as part of the EDC initiative. ABC uses innovative planning, design, materials, and construction methods in a safe and cost-effective manner when building new bridges or replacing and rehabilitating existing bridges. These methods improve constructability and work-zone safety while minimizing project construction duration and impacts to traffic. There are two metrics to gage ABC effectiveness including:
- On-site Construction Time: The time period from when a contractor mobilizes to the project site location to when all construction-related activity has ceased, and all materials, equipment and personnel are removed.
- Mobility Impact Time: Any time period when traffic flow is reduced due to onsite construction activities, ranging from hours to days, weeks, months and years.
ABC includes several different materials, techniques and systems to achieve the goals established by EDC. Three examples include the following:
Prefabricated Bridge Elements and Systems
Prefabricated Bridge Elements and Systems (PBES) are structural bridge components that are manufactured offsite and shipped to the site when needed, or built near the site and installed when needed. Use of PBES reduces onsite construction time and mobility impact time relative to conventional construction methods. PBES also include innovative design and high-performance materials such as Ultra High Performance Concrete (UHPC) and self-consolidating concrete (SCC). Because they are built off the critical path and under controlled environmental conditions, PBES provide improved safety, quality, and long-term durability.
Prefabricated Bridge Elements
Prefabricated bridge elements are individual structural components that reduce or eliminate onsite construction time needed to build a similar component using conventional construction methods. Elements are typically manufactured in a prefabricated and repeatable manner to offset costs. They are also manufactured under controlled environmental conditions which eliminates weather related impacts and improves product quality and long-term durability. Prefabricated bridge elements can provide flexibility for constructing a bridge by giving contractors options for erecting the elements to best suit their means and methods. They also eliminate typical field construction activities such as installing forming, overhang brackets and reinforcing steel, and placing and curing concrete. Prefabricated bridge elements include: decks, beams, piers, abutments, wing walls, foundations and miscellaneous items such as approach slabs and parapets.
Prefabricated Bridge Systems
Prefabricated bridge systems include an entire superstructure and substructure, or a total bridge that allow traffic operations to resume after installation. They generally offer less traffic disruption; greater safety for motorists and construction workers; and enhanced quality of work and constructability. Systems that include the deck and parapets already in place are preferable to eliminate any additional construction after placement. Due to the manner in which they are installed, prefabricated systems require innovations in planning, construction staging, engineering design, and use of high-performance materials.
Structural Placement Methods
Structural placement methods for the construction of PBES are dependent on access and site conditions, and the size of the project and structure to be built. Prefabricated elements are generally placed with traditional equipment such as cranes, gantry cranes and other lifting equipment. Due to their size and complexity, prefabricated bridge systems require conducive site conditions, and specialized equipment and placement techniques. Accordingly, prefabricated bridge systems are placed using a variety of equipment including: self-propelled modular transports (SPMTs), gantry cranes, barges and other equipment. Placement methods for bridge systems include rolling, launching, sliding, lifting, and floating a system into place with SPMTs or other equipment.
Geosynthetic Reinforced Soil-Integrated Bridge System
Geosynthetic Reinforced Soil-Integrated Bridge System (GRS-IBS) technology is an ABC geotechnical method that can be used for a variety of bridge applications. The system includes a foundation, a GRS abutment, and a GRS integrated approach to transition the roadway to the bridge. The GRS abutment consists of closely spaced layers of compacted granular fill material and geosynthetic reinforcing mats behind a wall facing element supported on a foundation. The wall element can include concrete masonry units, modular block, precast concrete panels, and steel sheet piling. The bridge superstructure can either be placed directly on the GRS abutment or on a concrete foundation incorporated with the GRS abutment. The GRS integrated approach consists of similar layers of compacted fill and geosynthetic reinforcing mats to support approach roadway paving. GRS-IBS has several advantages, which include simplified design and construction efficiency. It can be built in variable weather conditions with readily available labor, materials, and equipment and can easily be modified in the field. GRS-IBS has significant value when employed for small, single-span structures.
Wallace Montgomery and ABC
Since the FHWA launched the EDC initiative, WM has spent the last several years incorporating our 40 years of conventional bridge design and construction experience with ABC methodologies. We have also established an ABC Division within our Bridge Department led by a registered professional engineer with over 16 years of bridge design and construction experience. WM’s ABC Division has provided innovative ABC solutions on several bridge replacement projects for clients throughout Maryland and continues to look for opportunities on every project we undertake.