The FHWA 2015 R&T Story

Preserving the Nation’s Infrastructure

Trucks deliver concrete for the deck of the existing Paseo Bridge in Missouri as part of a project that used innovative design techniques to accelerate bridge construction.

Examples of FHWA research and innovation delivery activities: Accelerating Infrastructure Construction and Assessment Accelerating Bridge Construction to Reduce Congestion Improved Bridge Deck Condition Assessments via the RABIT™ Bridge Deck Assessment Tool Producing Low-Cost, Long-Lasting Rockery Retaining Walls Developing Rapid Post-Disaster Recovery Assessment

FHWA and Oregon DOT use accelerated bridge construction to rapidly remove and replace five bridges on Oregon 38. Rapid bridge replacement technology used hydraulic jacks mounted on a sliding rail to slide the old superstructure onto temporary supports and move the new superstructures into their final position. (Images: FHWA)

To keep pavement, bridges, and other types of infrastructure in a state of good repair, FHWA fosters innovations that increase longevity while enabling improved monitoring of road conditions.

As the Nation’s transportation infrastructure ages, maintaining the highway system in a state of good repair will become significantly more complicated and expensive. According to FHWA in 2012, more than 66,000 bridges in the U.S. were rated as structurally deficient. Structural deficiencies are characterized by deteriorated conditions of significant bridge elements and potentially reduced load-carrying capacity.¹⁰

The investment required to rebuild these bridges is estimated to be more than $51 billion.¹¹ FHWA’s research is forward-looking, and supports advancement of innovative materials and designs, improved infrastructure management and preservation practices, better construction techniques, and improved quality control to advance infrastructure safety, longevity, and environmental sustainability.

Research Activities

FHWA is pursuing a variety of research to address highway infrastructure challenges. For example, FHWA is researching new methods and processes to accelerate infrastructure construction, such as precast concrete deck panels in bridge construction. Efforts to help highway agencies effectively assess and manage infrastructure include pursuit of innovative tools to evaluate bridge deck conditions, and post-hazard assessment guidelines for flooded roadways. The research activities below illustrate FHWA’s important role in each of these areas with specific examples of innovative solutions.

Accelerating Infrastructure Construction and Assessment

Roughly 10 percent of the Nation’s 600,000 bridges require major rehabilitation, repair, or complete replacement.¹² The work that occurs on the construction site can significantly impact mobility and safety. In some cases, the direct and indirect costs of traffic detours or road closures as a result of bridge construction far exceed the cost of the structure itself.¹³

FHWA has initiated a number of projects to speed up or accelerate infrastructure construction and preserve existing infrastructure. FHWA research has led to the Accelerated Bridge Construction (ABC) processes, which include innovative planning, design, materials, and composite construction methods, in a cost-effective manner to build or replace bridges. As part of the deployment initiative, Every Day Counts, most States are using one or more ABC techniques. ABC can lead to reduced agency costs, improved motorist and worker safety, improved mobility around bridge construction projects, better initial quality if using prefab components, and more durable and lasting bridges. ABC technologies include the following:

Construction of the roadway surface nears completion on the Christopher Bond Bridge construction project in Kansas City, Missouri. The innovative side-by-side bridge constructive technique saved time and minimized road closures. (Image source: FHWA)

Placing of rebar prior to concrete pour during construction of a pylon on Christopher Bond Bridge construction project was one of many cost-effective, technical engineering solutions that saved time and provided flexibility in the bridge construction schedule. (Image source: FHWA)

• Prefabricated bridge elements and systems (bridge components built offsite, or adjacent to the alignment, reducing onsite construction time and mobility).
  
  
• Geosynthetic reinforced soil-integrated bridge system (use of alternating layers of compacted granular fill encapsulated by geotextile fabric sheets to build support for the bridge.)
  
  
• Slide-in bridge construction (new bridge built on temporary supports parallel to an existing bridge and upon completion the old bridge is demolished and a new bridge is slid into place, tied into the approaches, and paved within 48 to 72 hours).

The impact of using these innovations can be seen in the following examples:

• Nevada used slide-in bridge construction and shut down a road for only 56 hours to replace a bridge, saving an estimated $12.7 million in time and fuel costs for commuters.
  
  
• Sandy Township in Clearfield County, Pennsylvania replaced a bridge using the geosynthetic reinforced soil-integrated bridge system with its own equipment and workforce in only 35 days, saving months of detours and delays.

Accelerating Bridge Construction to Reduce Congestion

Conventional bridge deck construction follows an onsite sequential process: building the substructure, construction and placement of either steel or concrete superstructure girders, followed by concrete bridge deck curing. These activities can impede traffic flow, causing travel delays for the motoring public and reducing safety for drivers, pedestrians, and construction personnel. ABC strategies have gained traction because they shorten project delivery, enhance roadway safety, and protect the environment.

Prefabricated, full-depth concrete deck panels are increasingly used in ABC processes in which modular components of a deck are precast off-site and then joined together at the bridge construction site. Modular precast concrete deck panels improve the safety and efficiency of the bridge construction process. Roadwork can be completed overnight, on weekends, and during off-peak hours, reducing congestion, road closures, and work zones. Since October 2010, more than 2,496 replacement bridges have been designed or constructed using prefabricated bridge elements and systems. Successful applications of full-depth precast concrete deck panels include the US-24 Mississippi River Bridge in Illinois and the 24th Street Council Bluffs in Iowa.

Precast concrete deck panels are placed on top of concrete or steel bridge girders and a composite connection is formed with the girders. For panels placed on steel girders, they are connected using shear studs that were previously welded to the girders. Deck panels have pockets that fit around the shear studs and are then filled with grout or concrete to form a composite bond with the steel girder.¹⁴ For precast deck construction, it is advantageous to cluster the studs closer together and increase the distance between the clusters, which simplifies panel fabrication and constructability.

The RABIT™ bridge deck assessment tool is eight times faster than conventional methods at collecting data on the conditions of a bridge’s deck and subsurface. (Image source: FHWA)

FHWA is conducting full-scale static and fatigue tests of composite beams constructed with steel beams and precast concrete deck panels, seeking to increase the space between clusters to make conditions more favorable to precast concrete deck panel construction.

Improved Concrete Bridge Deck Condition Assessments via the RABIT™ Bridge Deck Assessment Tool

One way to reduce the number and cost of bridge rehabilitation projects is to identify the anticipated future condition concerns of a bridge deck. FHWA’s Long-Term Bridge Performance program developed a multifunctional research tool to better characterize the condition of bridge decks. The RABIT™ bridge deck assessment tool, invented jointly by FHWA and university researchers, deploys a suite of technologies to help FHWA researchers collect comprehensive data on bridge deck surface and subsurface conditions automatically and simultaneously.

The combination of surface/subsurface tools allows bridge engineers to quickly identify bridge deck areas of concern—corrosion, cracks, and other forms of infrastructure deterioration. Data collected by the RABIT™ bridge deck assessment tool are tagged with GPS coordinates for accurate location reference. Maintenance crews can use those coordinates to locate, inspect, and repair any damaged areas of the bridge deck surface or subsurface. The RABIT™ bridge deck assessment tool can collect data from approximately 4,000 square feet of bridge deck per hour using a combination of onboard nondestructive tools and image processing capabilities, which require a minimum of two people to safely operate. The same assessment using conventional handheld equipment and individual operators would require a minimum crew of five people to collect data at the same resolution as the RABIT™ bridge deck assessment tool. The conventional method is performed at a lower rate of approximately 500 square feet per hour, which would take eight times as long to collect the same amount of data. The RABIT™ bridge deck assessment tool also automatically collects, reduces, stores, and provides a visual representation of all data collected in near real time. In addition, the RABIT™ bridge deck assessment tool minimizes both traffic interruption and exposure of field personnel to hazardous conditions.

Producing Low-Cost, Long-Lasting Rockery Retaining Walls

In November 2006, FHWA developed innovative guidelines to build cost-effective and structurally sound rockeries. Rockeries, or dry stack walls, are rough, natural, onsite rock structures that are stacked and interlocked with no mortar, concrete, or steel. They offer a low-cost, long-lasting, safe, and visually appealing way to retain and protect earth-cut or fill slopes.

Prior to 2006, no standards, specifications, or other accepted procedures existed to provide construction or design guidance for rockeries; however, rockeries functioned well in many different types of environments, suggesting that excellent performance could be expected when certain conditions were met. A rational, tested design procedure was needed to provide designers and federal landowners with confidence that rockery structures could be used as part of modern highway engineering.

FHWA guidelines on building rockeries, like this one on State Route 153 in Utah’s Fishlake National Forest, have reduced the cost of building walls by as much as 50 percent. (Image source: FHWA)

FHWA produced design and construction guidelines to define and evaluate the stability of rockeries given specific geometries (height, base width, and batter); rock properties and placements; and backfill materials. The guidelines also include construction quality assurance steps, standard plan drawings, and construction specifications. Rockeries help meet sustainability goals by using onsite materials, and at the same time they deliver unique context-sensitive solutions. To date, more than 80 rockeries have been built following the guidelines, resulting in a cost of $20 to $30 per square foot, compared with $70 to $100 per square foot for conventional walls.¹⁵ A recent example from Fishlake National Forest in central Utah (constructed at $20 per square foot) is shown in the photo at the top of the page.

Developing Rapid Post-Disaster Recovery Assessment

Floods can cause serious damage to roadways, often undermining the integrity of asphalt, concrete, and gravel roads. After a flood, highway agencies must quickly assess the extent of damage and perform repairs necessary to safely reopen the highway and maintain traffic flow. FHWA is currently conducting research to develop guidelines that transportation agencies can use to evaluate flood impacts on pavements and how quickly damaged roads can be reopened to emergency vehicles. In pursuing this research, FWHA is drawing on the experiences of State agencies responsible for infrastructure impacted by flooding.

Preserving the Nation’s Infrastructure

U.S. bridges and highways make up one of the most complex and wide-ranging transportation systems in the world. Maintaining safe infrastructure and its integrity is a priority for FHWA. Infrastructure investments spur economic growth, create well-paying jobs, and enable citizens to reach necessary amenities more reliably and efficiently. FHWA is advancing new construction techniques, assessment tools, technologies, and more sustainable building materials to construct longer-lasting bridges and highways in less time with reduced costs.

For More Information

The following Web sites are provided for additional information, and further highlight the transportation challenges and FHWA activities discussed above.

Every Day Counts 2012 Initiatives: Accelerated Bridge Construction: https://www.fhwa.dot.gov/everydaycounts/edctwo/2012/abc.cfm.

Accelerated Bridge Construction Fact Sheet: http://www.ops.fhwa.dot.gov/WZ/practices/factsheets/factsheet16/index.htm.

RABIT™ Bridge Deck Assessment Tool Overview: https://www.fhwa.dot.gov/research/tfhrc/programs/infrastructure/structures/ltbp/ltbpresearch/rabit/index.cfm.

Final Report – Rockery Design and Construction Guidelines: http://www.cflhd.gov/programs/techDevelopment/geotech/rockeries/documents/01_Rockery_Entire_Document.pdf.

¹⁰ Federal Highway Administration (2013). “Estimated 2012 Costs to Replace or Rehabilitate Structurally Deficient Bridges.” (Web page) Washington, DC. Accessed online: September 26, 2014. (https://www.fhwa.dot.gov/bridge/nbi/sd2012.cfm)

¹¹ Federal Highway Administration (2013). “Estimated 2012 Costs to Replace or Rehabilitate Structurally Deficient Bridges.” (Web page) Washington, DC. Accessed online: September 26, 2014. (https://www.fhwa.dot.gov/bridge/nbi/sd2012.cfm)

¹² Federal Highway Administration (2013). “Estimated 2012 Costs to Replace or Rehabilitate Structurally Deficient Bridges.” (Web page) Washington, DC. Accessed online: September 26, 2014. (https://www.fhwa.dot.gov/bridge/nbi/sd2012.cfm)

¹³ Federal Highway Administration (2013). “Accelerated Bridge Construction.” (Web page) Washington, DC. Accessed online: February 18, 2015. (https://www.fhwa.dot.gov/bridge/abc/)

¹⁴ Ocel, J. and Provines, J. (2014). “Strength and Fatigue Resistance of Clustered Shear Studs.” Proceedings of the 2014 World Steel Bridge Symposium. March 26-29, 2014, Toronto, Ontario.

¹⁵ Federal Highway Administration (2015). “Research and Technology Agenda. Meeting the Challenge: Federal Lands.” (Web page) Washington, DC. Accessed online: February 18, 2015. (https://www.fhwa.dot.gov/research/fhwaresearch/agenda/researchareas.cfm?urlanchor=federalLands#newhd3)