Accelerated Bridge Construction

Bridge owners are rolling, sliding and lifting prefabricated bridge segments into place — in some cases reducing multiyear projects to three-day weekends

In October 2009, the Lake Champlain Bridge was unexpectedly closed due to irreparable pier cracking below the water level. The shutdown meant area residents would have to navigate an 85-mile detour to reach life-saving emergency services, jobs, childcare, shopping and loved ones. 

The New York Department of Transportation and the Vermont Agency of Transportation, bi-state owners of the bridge, knew the closure would affect constituents’ lives. But, in the transportation world, safety trumps mobility. 

“No one wants to make the decision to suddenly close a workhorse bridge,” said Chris Price, HNTB bridge practice leader. “But with more than 600,000 bridges in the U.S. needing to be replaced, widened or rehabbed, more and more owners will need to do so.” 

The economic and daily life burdens on the residents of Crown Point, New York, and Chimney Point, Vermont, are known as user costs—risks that did not exist when most bridges were built on new alignments 50 or 60 years ago. To tame those risks, owners need solutions that accelerate bridge repair and replacement. 
And now they have them.

The Transportation Research Board and the American Association of State Highway and Transportation Officials believed user costs could be reduced dramatically if bridges could be constructed faster. In 2006, they initiated the second Strategic Highway Research Program to evolve accelerated bridge construction from an isolated, one-and-done practice to a mainstream renewal method. 

Working with TRB and AASHTO, HNTB and a team of subconsultants, including Iowa State University, embarked on a six-year program to develop a suite of standardized ABC products. They reviewed individual standards and specifications from pioneering states, identified best practices and eliminated obstacles. 

In 2012, the Strategic Highway Research Program Report S2-R04-RR-2: Innovative Bridge Designs for Rapid Renewal: ABC Toolkit was published, changing the way the industry views bridge construction. 

The ABC Toolkit guides bridge owners through implementation. Users will find descriptions of standardized approaches to designing and constructing complete bridge systems for rapid renewals in addition to: 
• Design standards and examples of completed prefabricated bridge systems for routine bridges with span lengths of 40 to 130 feet 
• Sample specification language for ABC systems, which adheres to AASHTO’s LRFD Bridge Design and Construction Specifications 
• Erection concepts for prefabricated bridge systems 
• Slide-in construction concepts 

“ABC uses innovative methods of planning, design contracting and construction to dramatically reduce mobility impacts—bridge replacement projects that took years can be constructed in a matter of days!” said Bala Sivakumar, PE, director of special bridge projects for HNTB and the author of the ABC Toolkit. 

With ABC, activities are performed concurrently and in a controlled environment to quickly and efficiently design, procure, fabricate and erect replacement bridge systems. The result often is a faster construction schedule. 

“That’s important,” Sivakumar said. “Although shorter project durations often are a common attribute of ABC, its mission is to minimize traffic disruption by moving construction away from traffic and building as much of the new bridge as possible offline.” 

The toolkit groups ABC design concepts into five classes based on mobility impact duration: 
TIER 1: Projects can be completed in 24 hours 
TIER 2: Projects can be completed within three days 
TIER 3: Projects can be completed within one to two weeks 
TIER 4: Projects can be completed within three months 
TIER 5: The overall project schedule is reduced from years to months 

Each tier dictates the type of technology the owner will use. For example, a Tier 1 project would use a slide-in construction method, whereas a Tier 3 project would require on-site assembly of prefabricated bridge elements and systems. 

“The toolkit takes a lot of the risk out,” Price said. “There is nothing more reassuring to cashstrapped transportation agencies than to hear, ‘This method works, and here’s how to do it.’ It elevates ABC to a more reliable position.”

The ABC Toolkit was deployed on two demonstration projects. The first: Iowa’s U.S. 6 Bridge over Keg Creek. The 1953 structure, 20 miles outside of Council Bluffs, was due for replacement and had a size and span configuration typical of bridges needing replacement in Iowa. It was the perfect demonstration candidate. 

The Iowa Department of Transportation prefabricated nearly 100 percent of the bridge components, including modular superstructure units with precast barriers and backwalls; precast concrete pier caps and columns; precast abutments and wingwalls; and precast concrete approach slabs. The prefabricated elements were delivered to the construction site over a period of one to two weeks and assembled like Legos®. The drilled-shaft foundations were the only components cast in place and were completed prior to closure.
Within a 14-day implementation, the Tier 3 ABC project delivered a new bridge from foundation to modular concrete-steel composite superstructure, eliminating a six-month bridge closure and a 14-mile detour. 

According to Sivakumar, the construction cost alone was 25 percent higher than the DOT’s original estimate, but when you consider the savings in eliminating the temporary bridge and user delay costs, ABC was the lower cost option.

In late 2013, the New York State Department of Transportation implemented a Tier 1 demonstration project, replacing twin (east- and westbound), 135-foot-long, three-span, steel composite girder structures on Interstate 84 over Dingle Ridge Road. Using the toolkit’s guidance for lateral slide design and construction, each bridge was replaced in a single weekend night. 

Expediency was paramount. The section of I-84, which connects New York and Connecticut, is heavily traveled, carrying approximately 75,000 vehicles a day. 

“We had planned to replace the bridges conventionally in two nine-month construction seasons,” said Bill Gorton, NYSDOT regional director. “ABC cut the project length in half, reducing traffic impact dramatically.” 

Using a precast replacement deck, the new bridges were constructed directly adjacent to the existing bridges. Crews slid the new structure into place using bridge movement technology specifically designed for overnight replacements. Only 10 months after the construction contract was awarded, the lateral slides for the I-84 bridges over Dingle Ridge Road were completed. The project for the two bridge slides only required two 20-hour weekend closures—one closure for each structure. 

According to Gorton, NYSDOT paid a premium for the lateral slide technique compared with traditional costs. However, the department was able to reduce the contract’s duration, and by avoiding the cost of erecting a temporary bridge, the DOT saved taxpayers $2 million. The savings would have been substantially higher if user delay costs were recognized. 

Bill Moreau, former chief engineer for the New York State Bridge Authority, said standardizing ABC approaches with the toolkit is worthwhile. 

“It allows agencies to tailor the concepts to the job and specific needs,” Moreau said. “You don’t have to reinvent the wheel every time you do an overpass.”