What does it take to slide two concrete 3.5 million pound bridges into place?
Well, according to the engineers who designed it and the construction workers who built it, all you need is several hydraulic jacks and about 14 gallons of blue Dawn dish soap.
That was the news at a gathering of state and local officials Monday celebrating the completion of the Fourth Street bridge expansion project, which used an innovative technique to complete it in a matter of days instead of months.
Preforming what is called a bridge slide, construction crews built two sections of bridge just to the east of the old structure. The two sections were then slid into place over the course of about two days, said city project manager Jeremy DeGeyter.
That process doesn’t use wheels or a crane. Instead, hydraulic jacks slowly push the bridge into place on steel runners that rest on temporary rubber and Teflon pads, DeGeyter said. Once it is in place, the Teflon pads are replaced by permanent concrete ones.
“It's not to say there weren't any nervous times. That moment when the jacks begin to push against the bridge and we wait to see if the bridges will actually slide, regardless of what all the plans and calculations of prior work say, that's an intense moment to say the least,” DeGeyter said.
And that’s where the dish soap comes in, said Jake Bottcher, the project manager for FNF Construction, which was tasked with building the project.
Bottcher said that at first they were having trouble getting the bridges to properly slide into place.
The solution was simple. FNF engineer Nate Eldodt drove down the street to Walmart and bought several gallons of soap that they used to lubricate the bridges and slide them in place.
FNF Superintendent Andrew Gofourth said that during other bridge slide projects, they have used other heavy-duty lubricants, but Dawn dish soap works the best -- and it has the added benefit that they can simply wash it away when they are done and it is not too bad for the environment.
The project expanded the bridge to accommodate four lanes on Fourth Street and potential future widening on Interstate 40, which runs under the bridge. On top of that, the project expanded pedestrian access on the bridge, building in a dedicated sidewalk and multimodal path, separate from the road.
The total cost of the project for both bridges was $13.9 million, although the City of Flagstaff pitched in some additional money for the cost of the pedestrian paths and to make the bridge more handsome.
Flagstaff Mayor Coral Evans told a socially distanced group of local and state officials that the expanded bridge eliminates the bottleneck created by the old bridge and better accommodates the 17,000 vehicle trips that pass over the bridge every day.
That number is likely to increase as Flagstaff grows to an estimated 25,000 vehicle trips each day, Evans said.
Now that the bridge is completed, DeGeyter said, the city will begin work on expanding Fourth Street to the south between its intersections with Soliere Avenue and Sparrow Avenue.
The city expects to hire a contractor this winter, with work beginning spring 2021. DeGeyter said they will likely begin working to extend the water system to the south alongside Fourth Street once a company is brought on and before the road expansion work begins.
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