Construction is now complete on the $1.75 billion highway reconstruction project 30 miles south of Salt Lake City in Utah County, USA, using the Accelerate Bridge Construction (ABC) methodology.
The 24-mile project calls for complete reconstruction of the existing roadway and the addition of two new lanes in each direction. The existing pavement has outlived its useful life, and the new road needs to meet future traffic demand. At the time of writing, completion of the project was scheduled for December 2012. At the current pace, design/build contractor Provo River Constructors will finish on that aggressive schedule.
One of the ways that contractors had been meeting and beating schedules is through Accelerated Bridge Construction (ABC) methods. In the past Utah Department of Transportation (UDOT) has used ABC to slash an entire construction season from a project schedule. For this project, Provo River Constructors is using ABC to build six new bridges off-line. Four of those bridges carry cross streets and two of them are mainline Interstate bridges.
As will become evident, ABC puts a premium on accurate surveying.
With ABC, a bridge superstructure is built in a precast area that is off the main roadway but near to its permanent location. Then equipment move the entire bridge, from girders up through the deck and parapet walls, into its permanent position in one huge piece.
Advantages of the ABC off-line method
This off-line method of bridge construction offers three major advantages:
- Less disruption of traffic;
- Faster construction, and;
- Worker safety.
It is useful to look at the surveying required for the ABC. “When we lay out the pier and abutments, we calculate their position in the office, and upload that onto our surveying equipment,” says Dan Leslie, survey area manager for DEI Professional Services. “Then we go into the field and lay out the corners of the abutments and wing walls, and for the centre bent we lay out the foundation corners and the centreline of the columns.
The contractor grinds down the concrete on the abutments to the correct elevation. Once it’s ground down, they’re ready to move the bridge.
For this Provo Centre Street bridge the prefabricating of the superstructure is at exactly the same elevation as it will be in its final permanent position. That eliminates the chance that somebody will neglect to calculate a change in elevation when converting the numbers from the superstructure to the abutments. The design surface is compared to the actual elevations of the tops of the girders and given to the carpenters to finally cut or fill in the concrete over the girders.
Jason Kack, a principal and survey division leader, says what satisfies him most about the Provo Centre Street Bridge is that it fits precisely into place. “We had not done an ABC bridge prior to this bridge, so we learned the process,” says Kack. “Our biggest challenge was to make sure that our quality controls were 100 percent, because if you move the bridge and it doesn’t fit, it’s a problem. So we’re very pleased that the bridge fit and that we met the project schedule. And we’re proud to be a part of the Provo River Constructors team.”
Belgian contractor Sarens, working with Provo River Constructors, took just 1 hour and 28 minutes to move the shorter span of the Provo Centre Street bridge into place. Sarens used two trains, each with 18 axles, to move the bridge.