Constructed in the late 1960s, the twin eastbound bridges that intersect Herman Street, Clinton Street, Jo Johnston Avenue and Charlotte Avenue in downtown Nashville were showing advanced signs of deterioration. Though all of the structures exhibited some degree of deck failure, the Charlotte Avenue bridge experienced three major deck failure issues during the summer of 2013. This required the closure of multiple traffic lanes and an emergency weekend closure to replace two bays of the existing deck. Recognizing these four pairs of bridges along I-40 required immediate attention, Tennessee Department of Transportation (TDOT) selected GS&P as lead design engineering firm for the $62 million bridge rehabilitation project. The scope of work included comprehensive site investigation, structural analysis and design, preparation of detailed roadway and bridge construction plans, technical assistance and research, and detailed traffic management plans.
“It’s not uncommon for bridges that were built half a century ago to experience functional failures,” says senior structural engineer Ted Kniazewycz. “In the case of the existing I-40 bridges on this project, all the decks were showing consistent issues with their performance. This prompted TDOT to realize that an Accelerated Bridge Construction [ABC] project had to be executed to address these issues.
“The Department wanted to complete the project within a compressed schedule to minimize the social and economic impacts to Nashville’s central business and entertainment districts, which are continually generating huge traffic demands on I-40. By using ABC versus a more traditional delivery method, it was estimated the project could be completed within a total of 13 weekend full-closure periods instead of up to three years of reduced traffic lanes.”
Along with ABC, Construction Manager/General Contractor (CM/GC) project delivery was selected for the effort. This involved GS&P, TDOT and general contractor Kiewit Infrastructure South Co. working together to find the most reasonable cost for the project as well as the optimum methods for completing the reconstruction of the various bridge elements.
“We identified four to six potential solutions for rehabilitating each of the four pairs of bridges assessing criteria such as costs, materials, constructability, life-cycle analysis, risk factors and traffic/railroad impacts,” explains senior transportation engineer Larry Ridlen. “This evaluation process was an incredibly valuable tool in ranking the various site-specific options and identifying which should move forward for further consideration. At the end of the day, material procurement played a pivotal role in the selection of final options for each of the bridges in respect to the accelerated schedule.”
No Two Bridges Alike
With the evaluation factors considered for the four crossing sites, the selected construction method turned out to be unique for each location, with no two bridges requiring identical restoration solutions.
“For the Herman Street/NWR overpass, we decided to replace the existing superstructure with steel-beam superstructure units,” says Kniazewycz. “For the Clinton Street/CSX crossing, we chose a superstructure replacement of two spans with prestressed concrete bridge elements and the elimination of four spans. For the Jo Johnston bridge, we selected a superstructure replacement of one span with prestressed concrete bridge elements and the elimination of two spans. For the Charlotte Avenue overpass, we decided to replace the entire bridge with a single-span steel structure.
“I think the single-biggest project challenge was that each bridge had to be looked at individually in regard to how it was going to be accomplished. For example, the two 600-ton capacity cranes used for the Charlotte Avenue bridge had to be brought in from Canada. The contractor had to determine when those cranes were available, and our team worked backward from that date to make sure everything came together from a schedule standpoint. On the whole, the contractor had to look at the project through a holistic lens regarding what it would take to make things happen in the field.”
Working for the Weekend
To deliver the project in the anticipated 13-weekend period, GS&P employed numerous innovative engineering techniques on the four sets of bridges. Kniazewycz explains:
“We utilized structural steel superstructure units on the Herman Street overpass that were longer, wider and heavier than any comparable project that had been completed to date. These units were designed to be fabricated off-site, transported, and then installed during a single weekend closure period. In designing the superstructure units, we paid particular attention to standardizing the construction details to reduce the risk of fabrication and fit-up issues, which can be both costly and time consuming.
“Another method to accelerate the replacement of a bridge is to reduce the amount of bridge there is to replace. To achieve this, the team utilized span elimination on six of the eight bridges, which not only reduces the amount of bridge construction during a weekend, but also lessens the amount of maintenance required in the future.”
Precast concrete bridge elements were also used on six of the eight bridges as a means of accelerating the overall bridge construction timeline. These included prestressed box beams, full-depth deck panels, precast concrete end walls and precast approach slabs. All components were fabricated off-site and shipped to the location just prior to weekend installation.
“Careful planning before the weekend closures played an important role in the project’s success,” notes Ridlen. “Not only were the plans well-developed, but there was a lot of discussion prior to execution regarding what would happen during the weekend closures—especially that first weekend.”
“Deciding exactly when those closures would take place was also key,” adds Kniazewycz. “Major weekend events that would be negatively impacted by an interstate closure—such as the CMA Music Festival—were factored into the weekend closure decisions to minimize impacts to local residents. When a weekend was identified for construction, alerts were issued to the public as soon as, and as often as, possible regarding interstate closures and detours. We also analyzed traffic patterns and selected I-440 and state Route 840 as alternative routes around downtown Nashville so we could divert as much traffic away from the project site as possible.”
Weekend planning and scheduling also included the coordination of multiple subcontractors, suppliers, labor and equipment. Detailed hourly schedules and hour-by-hour snapshots of the ongoing work were tools used to accomplish the weekend work within a 58-hour closure window.
“Each weekend closure started out with bridge demolition, which was scheduled to be completed within a 12-hour period so reconstruction activities could begin,” says Kniazewycz. “At times, both cranes and excavators were used on a single overpass in order to have enough resources to remove the bridge in time. As the project moved through the various weekends of construction toward completion, the crews were able to meet, and in most instances, beat the project requirements to have the interstate open in time for Monday-morning rush hour.”
Looking out for the Environment
Along with leading-edge engineering techniques, GS&P incorporated numerous environmentally conscious elements into the effort.
“The project promoted the reuse of the steel beams and rebar from the existing bridges,” says Ridlen. “Additionally, the demolished concrete from slabs was used as supplemental fill materials, and the new bridge designs utilized weathering steel, which doesn’t require painting and is much better for the environment.”
Most notably, GS&P—in partnership with TDOT, Kiewit, Irving Materials, Inc., and Middle Tennessee State University’s Concrete Industry Management Program—developed a high-strength, ready-mix-type concrete that reaches 4,000 pounds per square inch in just four hours. After that time, a bridge can be opened to traffic.
“The mix design was approved for use on the project as TDOT Class X concrete, and will be available to be utilized on future ABC projects throughout the state,” says Ridlen. “This special concrete composite can be batched from a plant and delivered by truck, which ultimately saved more than 36,000 concrete bags from the waste stream.”
A Fast-Paced Three-Dimensional Puzzle
Completed seven months ahead of schedule and utilizing only 10 weekend closures as opposed to the allotted 13, the Fast Fix 8 Accelerated Bridge Construction project restored four sets of mainline I-40 bridges in downtown Nashville with minimal impact to the environment, local businesses and residents, and the traveling public.
“In the end, four different pairs of bridges with four different rehabilitation solutions, along with an ABC approach, equaled a challenging, fast-paced three-dimensional puzzle,” says Kniazewycz. “Our success was supported by the hard work and seamless communication of all parties involved. I am most proud of our team’s ability to meet the aggressive schedule. We had 57 days to generate final design plans for the eight bridges in total. Not only was this completed in 57 days, but those days fell over the Thanksgiving and Christmas holidays.”
“GS&P was totally committed to the success of the project and worked long hours designing and redesigning the bridge elements to meet the capabilities of the contractor as well as doing what was best for the project and owner,” says Wayne J. Seger, P.E., TDOT Structures Division Director. “The team’s professionalism and design expertise, along with their flexibility and cooperation, made the Fast Fix 8 project a huge success for TDOT and the people of Tennessee.”