AASHTO Journal, 13 March 2015
The first use of a “bridge slide” construction technique by any tribal nation in the United States drew about 100 industry professionals from across the country to view the project at the Gila River Indian Community south of Phoenix.
That technique, which is among the advances to come out of the second Strategic Highway Research Program, or SHRP2, involved sliding together newly manufactured bridge sections with hydraulic jacks. This type of “accelerated bridge construction” allows crews to put a new bridge in place with a fraction of the traffic disruption periods required in traditional construction methods that build new facilities entirely in place.
Crews and observers watch Sacaton Bridge section slide into place.Matt DeMarco, SHRP2 renewal program engineer at the Federal Highway Administration, said this Sacaton Road project was the first to use the bridge slide technique in Arizona as well as a first for a tribal nation.
And Pamela Hutton, SHRP2 implementation manager at the American Association of State Highway and Transportation Officials, said the Feb. 24-25 event drew the largest attendance so far for a SHRP2 bridge project showcase.
That meant those attending could see the last of four bridge sections put into place under this technique, along with the technique’s potential for saving time in construction days and delays to roadway users through road closures and detours.
The showcase audience included more than 30 from the Arizona Department of Transportation, plus attendees from state DOTs in New Mexico, Nevada, Oregon, Washington state and Michigan.
Using a SHRP2 design “toolkit” and concepts from the SHRP2 report “Innovative Bridge Designs for Rapid Renewal,” the project closed the Sacaton bridge and detoured traffic for nine days. That compares with an estimated four to six months that would be needed for conventional construction, said Mark Chase, a vice president of AZTEC Engineering, which was one of two contractors on the project along with FNF Construction.
The previous 140-foot bridge was built in 1961 with a cast-in-place slab on precast rectangular beams, over a mostly dry river channel – though during flood events the water sometimes over-topped the bridge decks.
During construction of the new bridge, the older span remained open to traffic up to the final slide of new bridge sections. Then, once the old structure was demolished, two girders and bridge decks were “slid” together to form the new surface. A project website said FNF demolished the old bridge and slid the new bridge into place on Feb. 22-24, and captured the slide process in a video and progress photos. The new bridge opened to traffic in early March.
“It’s been a seamless process that I can’t say enough about,” said Tim Oliver, director of the Gila River Indian Community Department of Transportation. “It’s one of our busiest community roads. It’s critical that we do this in the most efficient way possible and that is what we were able to do.” He said the lengthy traffic detour that would have been required under conventional construction would be “a big impact on a small community.”
Officials said the project was originally planned as a conventional bridge replacement using a design-bid-build contracting process. AZTEC’s Chase said that at one point the project had stalled due to insufficient funding and lingering concerns over how long the road would have to be closed to build the new the new bridge.
However, the community received $2.2 million from the FHWA’s Tribal Transportation Bridge Program, while a joint FHWA/AASHTO Implementation Assistance Program awarded it an additional $500,000 to use the SHRP2 innovative product.
This bridge-slide process has been used in other states including Nevada, Utah and Iowa. “We were hesitant to consider a bridge slide – but FHWA told us of SHRP2 funding that we then applied for and received,” said Steven Johnson, senior civil engineer at the Gila River Indian Community DOT.
“Once we started investigating the SHRP2 toolkit,” he said, “we realized that the best way to determine the most appropriate design and construction method for this bridge would be to work with both the designer and the contractor simultaneously.” Johnson said the FHWA helped the tribal DOT line up a construction manager/general contractor funded through the Tribal Transportation Program.
“After extensive analysis of the ABC alternatives, it became obvious that the bridge slide would be the most economical solution,” he said. “It’s been a dream job that has gone very smoothly.” Johnson also said the final cost was the same as if they had built a conventional bridge, but with added benefits including reduced closure times.
“I had the impression that to qualify for the SHRP2 funding, we would have to use the SHRP2 toolkit by applying its standard plans,” said Chase. “Instead, the toolkit provides central concepts; it includes standard plans, but it doesn’t force the design to use them. That way, we could modify them to meet our needs or create our own. The intent of the toolkit isn’t so much to provide a recipe, but rather a philosophy.”
“In some respects, it was super low-tech,” said DeMarco, since all the jacking equipment needed to slide the sections together fit into a single box. He said besides cutting construction time, there was a “huge savings in user costs,” since at a construction project things like “traffic controls, rerouting vehicles, delays due to detours, gas costs and freight delivery costs all factor into the value.”
The SHRP2 program began as a $238 million federally funded research effort in various transportation capacity, reliability, safety and renewal technologies, and has received $169 million in funding to help states and tribal nations puts its research to use in the field.
Already, seven other transportation agencies have received implementation assistance funds to reconstruct bridges using SHRP2’s innovative bridge design concepts.
