Precast Bridge Abutments Cut Construction Time

Story and Photos by Mike Larson, Editor | September 28, 2010

New pre-cast, segmental bridge abutments being put together on State Highway 63 near the western Wisconsin village of Baldwin may be the first step in giving Wisconsin highway builders a way to build bridges up to 30 percent faster than the normal form-and-pour method they commonly use now.

The abutments, each consisting of seven pre-cast panels mounted on pilings, are the first pre-cast, segmentalabutments ever used in a Wisconsin Department of Transportation (WisDOT) highway project.

If the concept works as planned, it could eventually be approved for general use in WisDOT projects.

This first co-operative application of the technique is being spearheaded by the University of Wisconsin-Madison's engineering department and WisDOT.

Alfred Benesch & Company, Kenosha, WI, designed the bridge, including the pre-cast abutments, as a subcontractor to the university. Edward Kraemer & Sons, Inc., Plain, WI, is the prime contractor for the bridge project, which also includes a box culvert about a mile further up the road.

Technique Could Put Up Concrete ForAbutments In Two To Three Days

Michael Oliva, professor of engineering at the UW-Madison, says the major benefit of using segmental, pre-cast bridge abutments is quicker assembly and controlled quality.

Demolition And Construction Done In Stages

David Koepp, WisDOT's manager on the project, says the construction plan calls for Kraemer to demolish and rebuild one lane at a time, so there will always be one lane available to carry traffic throughout the project. Traffic from each direction is controlled by stop lights at the ends of the construction zone.

“If we'd demolished the whole bridge at once,” he says, “all traffic, including emergency vehicles, would have to detour eight miles to get around the construction site. So we always need to keep one lane open.”

Work Moving Along

Kraemer is completing major construction for the project with a crew of four and one 100-ton lattice-boom crawler crane that handles a wrecking ball, clamshell bucket, pile driver, 1-1/2-cubic-yard concrete bucket, and all the lifting.

Kraemer began demolition of the western half of the existing bridge in September, and the entire project is scheduled for completion by early November.

After demolishing the western half of the existing bridge, Kramer drove 12 40-foot-long steel H piles into the creek bed until each reached 72-ton bearing capacity. Each pile was spotted and double-checked using a GPS system.

To be certain the pilings would align with the pockets in the pre-cast panels, each pile had to stand within 1-1/2 inches of vertical over its full height.

Driving all of the pilings for the western half of the bridge took just one day.

After the pile driving had been completed, Kraemer excavated and filled around the piles with washed stone to provide a bearing surface for the wall sections.

First Panels Set In About 30 Minutes Each

The first three abutment panels were set on the morning of September 26. The two wall panels weighed 29,500 pounds and 30,900 pounds, while the wing wall came in at 40,400 pounds. All three pieces had been cast and cured for 30 days at Spancrete's facility in Green Bay before being trucked 235 miles to the site.

As each piece arrived, Kraemer's crew picked it off the truck, placed it over the pilings, and aligned it in about 30 minutes.

Said Proffitt, “The pockets in the panels slid over the pilings easily, and final alignment of the panels went quite quickly. We checked them with a laser transit, and all ended up right on the money.”

Deck To Be Cast In Place

The abutments and deck for the western half of the new bridge are scheduled to be finished by early October. The process will then be repeated for the eastern half of the structure.

Unlike the abutments, however, the deck will be constructed using the conventional cast-in-place method, which entails forming, placing rebar, and pouring and curing concrete.

Overall, using the pre-cast abutments is expected to reduce the overall construction time by about 30 percent, compared to forming, casting and curing them in place.

Potential Strong For Even Larger Time Savings

Says Professor Oliva, “Pre-cast bridge abutments could well provide Wisconsin's bridge designers and builders with another effective method for meeting the state's highway needs.”

“We need to monitor how this bridge performs over time to know for certain, but the abutment construction seems to be going as well as expected.”

Oliva says that using pre-cast bridge abutments would offer an especially large advantage for contractors when building abutments that sit in water. That's because the bottoms of the pile voids could be plugged and the piles grouted without having to build and later dismantle a cofferdam.

Further gains in speed could come, he says, by combining a pre-cast deck with the pre-cast abutments. “Eventually, we would like to also make the bridge deck of pre-cast panels. Using pre-cast abutments and pre-cast decking together would enable a contractor to assemble an entire bridge in just a few days,” said Oliva.