Tag Archives: bridge

Using History to Predict Bridge Deck Deterioration

Just how long will it be before a bridge deck needs to be rehabilitated?  Why not look to history to find out?

Researchers have put several decades of MnDOT bridge inspection records to good use by analyzing old bridge deck condition reports to calculate how quickly similar bridge decks will deteriorate.

MnDOT inspects bridges regularly, but had never used this historical data to help determine the rate of bridge deck deterioration and what factors influence it.

“We’re always trying to improve the timing of bridge deck repair projects and improve our understanding of what contributors affect the way our bridge decks deteriorate,” said Dustin Thomas, MnDOT’s South Region Bridge Construction Engineer.

Data-Crunching

From their analysis, researchers created deterioration tables that can be used to better predict the timing and costs of repairs and maintenance.

Researchers looked at the inspection history and construction details of 2,601 bridges to determine the impact of factors such as type of deck reinforcement, depth of reinforcement below the driving surface, traffic levels and bridge location.

Using the inspection data, researchers developed curves that show how long a bridge deck is likely to stay at a given condition before dropping to the next. They developed separate curves for each variable that had a significant impact on deck deterioration rates.

What They Found

Several factors were found to have a notable impact on how quickly bridge decks deteriorate:

  • Decks without epoxy-coated bars built between 1975 and 1989 deteriorate more quickly than other bridge decks.
  • Bridges with less traffic showed slightly slower rates of deterioration than highly traveled bridges.
  • Metro area bridges drop to a condition code of 7 (good) more quickly than bridges in other parts of the state. This may be due to increased chemical deicer usage or because maintenance activities like crack-sealing are more likely to be delayed on larger metro bridges  because of the difficulty accessing middle lanes.
  • When a new deck is installed on an existing bridge, the deck performs like a brand-new bridge and so MnDOT should use the deterioration table for the re-decking year, rather than the year the bridge was originally constructed.

MnDOT plans to incorporate future bridge inspections into the dataset to enhance the predictive value of the deterioration tables.

Related Resources

The impact of overlays on bridge deck deterioration in Minnesota was not clear, but redecked bridges were found to perform similarly as brand-new decks.

Video: Load Testing for the Winona bridge

New video, below, shows how explosions are used to test the bedrock for the new Highway 43 bridge in Winona.

Bridge engineers use “pile load testing”  to find out how much weight and resistance the ground will bear. It not only saves time and money, but helps design a bridge that will sit securely on the bedrock, below the river.

The statnamic test used in the video is one part of this process.

Winona Bridge Statnamic Test

 

How load testing works: 

It begins with digging and pounding.

Two different kinds of piles are put into the ground:

  • A hollowed shaft, which is filled with rebar and concrete. It goes 30 to 50 feet below the bedrock to create a solid pillar that can assess how much weight and sway the ground will bear.
  • A steel pipe that is hammered into the ground. Since the bedrock is about 100 to 150 feet below the river, these pipes are welded together end-to-end to reach that length.

Once the piles are in, they’re tested two different ways.

  • Pile Dynamic Analysis, with gauges affixed to the top of the pile to read the pressure put on it when hit with a pile driver.
  •  A Statnamic test (shown in videos), which involves accelerating a heavy weight by setting off a controlled combustion reaction. This shows how much resistance the pile can take.

Once the data is collected for the bridge design, the piles are cut off two feet below the river bed.

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.

Related Resources