Rapid Replacement

March 31, 2008
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Last summer, an eight-lane bridge on Ottawa’s Route 417 was replaced in just 17 hours using SPMT, computer-controlled platform vehicles that move bridge systems weighing up to several thousand tons with fraction-of-an-inch precision. It was a feat that would normally take two years. As a geomatics and surveying crew with design and consulting firm Stantec worked under the gaze of hundreds of onlookers, the question on many minds was, “Will it fit?” That question could not be answered until the final moments of installation.



Accelerated Construction Technology combined with reflectorless robotic total station and digital level instrumentation aided the replacement of the Queensway Corridor in Ontario. Under a lighted project area, the second replacement bridge deck leaves the staging site.


Workers make last-minute efforts to separate the old bridge deck. Photo courtesy of Dufferin Construction Company.

Technology for rapid replacement projects is capturing attention across North America as the need to rehabilitate or replace tens of thousands of bridges--while maintaining traffic flow--is of growing concern to local governments. Accelerated construction techniques, such as the use of Self-propelled Modular Transporters (SPMT), are widely used in Europe and are gaining favor in the United States. The Island Park Bridge, part of Ontario’s and Ottawa’s main east/west Queensway corridor, represents the first attempt utilizing this technology in Canada.

Last summer, an eight-lane bridge on Ottawa’s Route 417 was replaced in just 17 hours using SPMT, computer-controlled platform vehicles that move bridge systems weighing up to several thousand tons with fraction-of-an-inch precision. It was a feat that would normally take two years. As a geomatics and surveying crew with design and consulting firm Stantec worked under the gaze of hundreds of onlookers, the question on many minds was, “Will it fit?” That question could not be answered until the final moments of installation.

The Stantec crew was responsible for traditional survey activities, including as-built surveys for pre- and post-construction, layout surveys for new construction, monitoring reports throughout construction and layout control during bridge replacement. The process--new to any city in Canada and to Stantec’s team--put the surveyors’ ingenuity--and nerves--to the test.

To tackle the project, Dufferin Construction Company formed a tight alliance with the Ministry of Transportation of Ontario (MTO) and Stantec’s geomatics division. Ryan Farrish, Dufferin’s project superintendent explains, “We spent an enormous amount of time doing the planning, surveying and engineering for the design and construction of the temporary supports and engineering analysis for both the existing and proposed bridge decks.”

From a surveyor’s standpoint, the job required extensive and continuous hands-on involvement, above and beyond a traditional assignment. “The contractor was relying on me for every aspect of this project, from initial conception to final placement,” says Bill Lawton, Stantec survey crew chief.


The Self-propelled Modular Transporter aligns the bridge deck with abutments.

Setting the Stage

Rapid replacement technology for bridge replacement is a construction staging technique in which a new structure is built in an enclosed area adjacent to the highway. In the Queensway corridor case, this took place at a park some 165 yards from the bridge site. When the new structure is ready, the existing structure is removed, and the new one is placed in position using heavy lifting technology.

While simple in principle, this deck-on-girder bridge replacement posed a number of challenges for Stantec surveyors: extremely tight vertical and horizontal tolerances; a skewed, diamond-shaped connection to the existing abutments; and a compounded north/south and west/east elevation slope across the decks. The challenge was further fueled by the knowledge that there was no room for error--major adjustments during the actual installation process were out of the question.

Construction of the new bridge sections took place from March to August 2007. During this time, Stantec’s role was to monitor construction of the two new four-lane bridges, each 82 feet long and 66 feet wide and weighing approximately 718 tons. The new spans were placed on temporary supports built to the same height as the existing bridge. Additionally, crews surveyed simultaneous rehabilitation of both abutments where more than 128 anchor bolts were placed to secure the bridge girders.

Throughout this pre-installation process, several project aspects challenged the survey crew, including alignment, elevation and configuration.

Alignment

Survey crews were responsible for transferring dimensions from the existing bridge to the site where the new sections were being constructed. This involved extreme accuracy to within 3/8 of an inch to ensure that the new sections, with eight girders per structure, fit precisely on the rehabilitated bridge abutments.

The bridge alignment has a compounded tilt slightly from north to south, with the south side girders about 2 1/2 feet lower, and west to east, with the east abutment 1 1/4 feet lower. Although versatile, the SPMT can only lift the bridge section an additional 2 feet. Therefore, the removal sequence dictated that the southern deck pass over the north abutment, which required monitored adjustments to the road bed. Further, precise calculation of the newly placed abutment bolts was required to ensure that the bridge did not grind them during the removal process and that the new plates would be correctly positioned to receive the new bridges. Thus, vertical as well as horizontal alignment was crucial.

Elevation

During construction of the new bridge sections in the staging area, the geomatics team ensured that the new bridge girders would match the varied slope elevation of their predecessors. As the girders were laid out in the field from the midsection outward, minor millimeter adjustments were noted and transferred to the bolt placements so final adjustments could be made prior to grouting.

Configuration

Compounding the complexity of the assignment was the configuration of the bridge. Instead of crossing the highway perpendicularly as most highways do (which would have meant installing rectangular decks), Highway 417 crosses Island Park Drive at an angle, so the new bridge spans are diamond-shaped.

The final placement of the new bridge deck spans revealed that they were a perfect fit.

Lift Night: Lights, Camera, Action!

“The key question on lift night was, ‘Will it fit?’” Lawton says. “Yes, we had provided numbers to the engineers and the construction team, but everyone was looking at me.”

As hundreds of people, including officials from the Ministry of Transportation, interested onlookers, and engineering, construction and survey crews, gathered under the klieg lights on Aug. 10, 2007, the installation activity commenced at 8 p.m. Contract terms dictated that the entire process be completed in 15 hours, which left no opportunity for major adjustments during construction. In fact, if the new bridge was not in place and open for traffic by 5 p.m. (21 hours later), the MTO reserved the right to cancel the operation and place the old bridge back in its original position in order to maintain traffic on this important thoroughfare.

The massive modular transport system rumbled into action. Consisting of a series of flatbed trailers that can be connected end to end to fit the size of a particular project, the two transporters used for the Island Park Bridge measured 138 feet long and had 216 rubber-tired wheels. Despite their size, the transporters were surprisingly maneuverable, with the ability to rotate 360 degrees, reach speeds of up to 3 mph and tilt a load by up to 2 feet for precise positioning. In addition, the SPMTs handle grades up to 3 percent and vertical faces, such as curbs, of 6-8 inches, while keeping its load horizontal.

First, the original bridge structures were removed and placed on temporary falseworks in the staging area. After a final check of the newly visible bolt placements, minor adjustments to the vertical alignment of the bolts were completed using shim plates of varying thickness. Bearing plates were laid, and the top of the plate was checked. Then, each plate was incrementally adjusted vertically to match the underside of the girder shoe plate.

Next, the new bridge sections were retrieved and carried to the overpass. When each new span was in the correct position, the transporter lowered it into place while crews bolted lateral restraining plates to secure the bridge into position.

To the relief of all involved, the new spans were a perfect fit. “This is the first time I’ve ever been hugged by a construction supervisor,” Lawton says.

At 8 a.m. the next morning, the new bridge was securely in place and final paving activities began. By 1 p.m., the first traffic lanes were open for business. The slight delay--from the 15 scheduled hours to the actual 17 hours--was not due to the placement of the bridge, but rather to the extreme heat of the day and its affect on the rollout of the asphalt lift.

Median concrete barrier walls were
positioned after the deck placement.

On-the-Job Innovation

The experienced survey team used Trimble (www.trimble.com) 5600 equipment for first-order survey work to an accuracy of 3 seconds and a Trimble DiNi Digital Level for accurate vertical measurements. From a surveying standpoint, the over- riding challenge was to ensure that the new bridge components would mesh precisely with the existing rehabilitated bridge abutment while construction of the bridge deck was in progress.

An essential factor in the project’s success was development of a machined template to ensure that each of the 128 bolts used to secure the bridge girders was installed in precisely the right spot. The 4-meter-long, 3/8-inch-thick steel plate was custom-designed by Stantec and constructed and verified onsite.

Analogous to an oversized tuning fork, the template allowed the crews to precisely place anchor bolts on the abutment configured to the new alignment. “We had never used a template like this before, but it worked very well,” Lawton says. “Access was a challenge. Some of the bolts we were placing were only eight inches off the rear wall.”

For the crew involved, it was a stressful but exhilarating experience. A conventional bridge replacement for a similar project would have taken up to two years with significant impact on traffic, Lawton explained. “But at the end of a traditional project you will have a bridge. With this process, if a serious mistake happens, you may end up with 718 tons of junk.”

Now with the first project under their belt, the survey crew members look forward to working on future rapid replacement technology assignments. And they may soon have their chance. At a total cost of $8.6 million, this construction technique is estimated to have saved the MTO more than $2.4 million over traditional techniques while avoiding the extensive disruptions to traffic flow. The ministry recently issued a contract for a second rapid bridge replacement project; Stantec has begun the survey work for the scheduled replacement in early August 2008.

“This sort of technology is not suitable for every bridge replacement,” says Dufferin’s Farrish. “You need a staging area close by. You have to be very concerned about overhead wires, the condition of the bridge and all the safety implications of carrying out a project of this magnitude. There is no room for error.

“But if the conditions are right, the benefits are significant. In fact, it’s surprising that it took so long to do this first project. It came down to having the courage to try it, and for that you have to give MTO credit. Now it’s up to other jurisdictions to see if it is applicable for their situations, too.”

Note:

Many U.S. states are now adopting Accelerated Construction Technology, or rapid replacement technology, for transportation projects, including those involving Self-propelled Modular Transports. The Graves Avenue Bridge project in Florida was the first use of SPMT on an interstate highway in the United States. This project involved the widening of Interstate 4 from four to six lanes. More information on rapid replacement technology can be found on the Federal Highway Admini-stration Web site at www.fhwa.dot.gov/construction/accelerated.

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