Nobody likes a detour. For recreational travelers, it may be just inconvenient. For a freight shipper, the out-of-distance travel costs money, adding to expenses and possibly raising prices for all of us.
The Iowa DOT has been exploring several accelerated bridge construction (ABC) technologies to reduce the closure time when a bridge is being replaced. Those projects included the use of precast concrete bridge components, such as precast piers, precast abutment footings, precast approach panels, and full-depth precast bridge deck panels. A recent project on Iowa 92 near Massena proved that using an entirely prefabricated bridge superstructure can considerably shorten construction time.
The Iowa 92 project consisted of replacing the existing 40-foot-long, single span, steel I-beam bridge that was constructed in 1930. The bridge was classified as structurally deficient and heavy loads were restricted from using it.
Conventional construction would have required a detour of 13 miles, seven of those would have been out-of-distance travel for customers. The 180-day standard construction closure could have cost customers $437,000 in user costs including time, gas and wear and tear on vehicles. Using the ABC technique of a lateral bridge slide of the prefabricated bridge superstructure, the closure time was cut to just nine days, reducing the user cost to $22,000.
Jim Nelson, transportation engineer manager in the Office of Bridges and Structures, saw this bridge replacement technique on a project on Interstate 80 in Utah in 2012. “We toured the project and asked a lot of questions,” he said. “The Utah DOT was very open with us and shared their experience. Using what we learned in Utah helped our project go well.”
The basic idea of a lateral bridge slide is that the new bridge is constructed on a removable framework beside the old bridge, while the old bridge remains in service. Once the new bridge structure is complete, the road is closed, the old bridge is demolished, and the new bridge slid into place.
While that sounds fairly simple, there are many intricate details that must be worked out prior to construction. Input from peers was seen as vital to the project’s success. The Iowa DOT, along with the Federal Highway Administration, hosted an Accelerated Bridge Construction Prefabricated Bridge Elements and Systems Lateral Slide Workshop to bring together subject matter experts from around the United States to meet with Iowa and Minnesota DOT staff. Nelson said, “There was considerable discussion at this meeting regarding the Massena bridge replacement project that was ultimately incorporated into the final concept and design of the bridge.”
In addition to the internal discussion among bridge designers, Nelson said the ABC methods also take more communication between the bridge designers and contractors. “When we started the design process for this bridge in September 2012, we talked about how to make the slide work. We originally wrote the specification to include sliding the bridge using stainless steel bearings and Teflon pads. This is the technique we saw demonstrated in Utah. Herberger Construction of Indianola, the company who won the bid, proposed using rollers as an alternative. They had rollers in their inventory from a railroad bridge slide they accomplished in the 1970s. The change in methodology took coordination and a lot of interaction between the DOT and the contractor, but it worked well and we both learned a lot in the process.”
Scott Nixon, resident construction engineer in Creston, said, “During the nine-day closure the contractor was required to remove the old structure and existing pavement, grade and reshape the river banks, place riprap on banks, drive piles, form and pour new abutments, slide the super structure into place, grade and pour new approaches and shoulders, and install new guardrail. The closure was a nine-day whirlwind. There were multiple contractors on-site during the closure. In fact they were still placing riprap while the bridge was being rolled into place. This took a lot of coordination between the contractor and their subcontractors. We had a meeting two weeks prior to the closure with all the subcontractors and stressed the importance of coordinating the work and being flexible on the timeline. Herberger was a little unsure on the time needed to drive the piles, so the timeline wasn’t necessarily set in stone. My inspection staff were continually communicating with the contractors to ensure they were on- site when needed, and were not delaying any of the work. In the end, the contractor was successful in getting all the required work completed and the bridge opened to traffic in nine days.”
The Massena bridge project demonstrates that an ABC project does not necessarily require expensive equipment or complicated design calculations to develop a cost-effective, easy-to-construct bridge that will ultimately save taxpayers time and money during construction.