Behind the bridge slide: dish soap and a lot of planning

Using Dawn dish soap to grease the rails, MnDOT crews inched the new Larpenteur Avenue Bridge into place two weeks ago using an innovative construction method.

As the bridge reopens to traffic tonight over I-35E, MnDOT celebrates the success of its first slide-in place bridge construction.

“The slide-in worked very well,” said David Herzog, MnDOT’s project manager for the I-35E Corridor – MnPass Project. “I think the process has given us the confidence to possibly use it again in the future.”

Slide-in technology

The slide-in method has been used in the past for railroad bridges and large bridges with high traffic and limited construction options. Now, state agencies and the Federal Highway Administration are applying the method to smaller, more routine bridges to minimize impacts to the traveling public.

Whereas the typical phased construction of a bridge builds one-half of the structure at a time, slide-in bridge technology allows the entire superstructure to be built at once, requiring just a brief, temporary closure of the highway.

Crews constructed the 3.5-million-pound Larpenteur Bridge right next to the existing bridge and then slowly slid it into place during the course of two nights. This effectively sped up construction from 110 days to 47 and reduced traffic impacts to drivers. (Watch video of the slide.)

The quality of the bridge also improves with this method, since it eliminates the deck construction joints and girder camber problems associated with phased construction, according to the FHWA. The pressure to use faster concrete cure times is also reduced.

History

With a quarter of the nation’s bridges in need of repair or replacement, the FHWA is pushing the slide-in method as a cost-effective technique that can cut construction time in half. It has previously been used in Oregon, Utah, Missouri, Michigan, Colorado and Massachusetts.

The concept has been around for more than a century, but slide-in technology is relatively new for small or medium-sized bridges, and it’s the first time MnDOT has attempted it on a state bridge.

Although MnDOT staff had flown out to Utah to view a slide-in, it was Burnsville-based Ames Construction that proposed reconstructing the Larpenteur Avenue bridge that way when it made its successful bid for the corridor project.

The slide-in method is about 15 percent more expensive, Herzog said, but it allowed the bridge to re-open in 47 days, versus 110 days.

Earlier this summer, Ames replaced the Wheelock Parkway and Arlington Avenue bridges in conventional fashion, although they were only closed for 65 days because they were constructed on a very accelerated timetable.

“Larpenteur is more of a major thoroughfare and we thought shortening the duration of its closure would be more valuable to  MnDOT,” said Steve McPherson of Ames Construction, who was brought in from Utah to oversee the corridor project.

The fast reconstructions will allow the company to complete the bridge replacements and highway reconstruction in just 120 days. Next year it’ll finish the other half of the corridor.

All three bridges are being replaced to make room for the new MnPASS lane on I-35E.

One of the drawbacks to slide-in technology is that it requires ample room to build the bridge on-site. An alternative is to construct off-site.

The new Maryland Avenue/I-35E bridge was built off-site, as was the Hastings Hwy. 61 bridge. It was then loaded onto a barge, floated down the Mississippi River and lifted into place.

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