Replacing a bridge in only six hours

Track time is always precious, even more so on a line such as GO Transit’s Lakeshore West corridor that handles 60,000 commuters a day in metropolitan Toronto. With increasing ridership making more capacity a necessity, GO decided to add a third track. One potential bottleneck was the Credit River Bridge, but engineers were able to meet that challenge.

According to GO Transit, “The Credit River Bridge along the GO Transit Lakeshore West corridor was widened the weekend of August 9-10 to improve rush hour service. The process took just six hours and new and innovative technology was used to install the pre-assembled bridge section, which adds a third main line track to the existing two-track bridge.”

The third track addition is part of a project to widen the Lakeshore West line to improve peak period service for the 60,000 GO Transit commuters who travel in and out of downtown Toronto each day.

The installation process provided a safer and more-cost-effective alternative to the more-common-practice of assembling the expansion over the bridge. As the bridge span was pre-assembled and slid into place overnight, GO Transit was able to complete the process without any interruption to its commuter service.

“Investing in transit infrastructure is part of our plan for the economy and of our fight against climate change,” said Ontario Minister of Transportation Jim Bradley. “Better service for GO Transit riders makes it easier for commuters to leave their cars at home.”

Construction began on this section of the corridor in April 2007, and is expected to be completed by November 2009. Upon completion, the improvements will allow for the introduction of more GO train service and help reduce delays during peak travel periods.

“Because of its unique assembly process, the Credit River Bridge project has been of particular interest to GO Transit riders, and we are pleased to have this important piece of this corridor’s expansion complete,” said Greg Ashbee, Rail Expansion Program manager at GO Transit.

The process used for the installation of the bridge for the third rail line over the Credit River was that the span was assembled on land and then slid into place. This process provided a safer and more-cost-effective alternative to assembling the expansion over the bridge and meant that GO Transit service along the corridor was not delayed or interrupted.

Support beams and strand jacks were installed at either end of the pre-assembled bridge span. Once the support beams were installed, the pre-assembled span was placed on four rail cars to move it along the existing Credit River Bridge to the installation location. The 329-ton span was then slid over the new foundation using hydraulic technology.

The support beams and strand jacks were removed after the span was set into place. The rail cars were then removed from the tracks, and the span was slowly lowered onto the bearings already in place on the existing bridge.

The installation was completed in conjunction with Western Mechanical Electrical Millwright Services, an industrial equipment support company from Barrie, Ontario, that specializes in heavy rigging. The entire installation process took approximately six hours one evening and was, for the most part, controlled by an on-site computer.

Starting the process

“We started conversations with CN and gave proposals for the bridge project,” said Mark Carney, structural engineer for Western Mechanical. “It’s CN’s bridge and they contracted with us. CN’s crews built the actual bridge. To show CN how we would do it, we created a video that goes through the whole process step-by-step.

“Western Mechanical does specialty projects, usually moving really big things, usually in different ways, as this bridge was done,” Carney said. “There’s usually a problem customers have for which they don’t have a good solution. One of the reasons they don’t recognize the solution is because our equipment is so different from everyone else’s.”

“CN did a lot of the work on the bridge, including the tower, and the abutments for the third track portion,” said CN spokesman Bryan Tucker. “Western Mechanical is a company we have worked with regularly to do other dimensional moves. Western Mechanical provided the expertise and we needed experts because of the way that this project was done and the narrow work window, which was less than six hours to move the pre-assembled bridge into place.”

The bridge was assembled away from the site, not in place. There was no false work near the track on land.

“One reason we did it this way was to avoid using false work,” Tucker said. “The river is used a great deal for recreational purposes, so we wanted to minimize the impact on the community people who use the river. And this was summer time, the period of peak usage.”

CN’s Rocco Cacchioti is the project manager for this project under Daryl Barnett, division engineer.

Carney continued: “CN could have built this bridge piece by piece, putting it out over the Credit River. That would mean they would have had two cranes sitting there for a minimum of a couple of months, with all work done at night because there are two live tracks right beside the new being put in. With night work, there would be a minimal amount of interruption. CN’s safety policy is to stop work when a train goes by and give full attention to the train. Instead of having guys hanging over the river with everyone in safety harnesses, instead of doing it at night and instead of having large cranes there for months, Larry and Dan Eisses of Western Mechanical suggested this process to CN.

“The original idea was to have men working safely just off the ground instead of over the river and doing it at regular times instead of nighttime, which was a tremendous savings for CN,” he said.

The night of the bridge

“What actually happened that night is we had to be done in five hours, 40 minutes,” Carney noted. “The last train went by at 1:40 a.m. The four rail cars to move the bridge were spotted at 2:15 a.m. The bridge was loaded at 3:15 a.m. and the train was in position at 4:15 a.m. The bridge was transferred to western rigging at 5:15 a.m. The track was to be cleared at 5:30 a.m. The bridge was to be lifted and weight taken onto the top of the towers by the strand jacks at 6:15 a.m., bolts removed from gussets at 7:15 a.m. and the bridge landed at 9:30 a.m.

“The bridge started in its laydown area and we set up a gantry track under the gussets on the corner of the bridge,” Carney noted. “We put in gussets to match the bolt pattern on the bridge, so we didn’t have to add any boltholes. Right underneath the gussets are the dollies. On the same side, further back there’s a hydraulically-driven set of wheels, something like a military tank or a bulldozer. That drives the bridge back and forth and that’s what drove it onto the cars on the tracks. The beam that went over the top of the railway cars stayed there for the ride as we brought it over the existing bridge and lined it up to where its new site would be. From there, we reversed the process, rolled the bridge off the cars onto the western rigging. Then we lowered it in place.

“There were strand jack trees and strand jacks, which are six-foot-tall cylinders, at each corner of the bridge,” Carney said. “The strand jacks actually communicate with each other and with a central computer. One central computer is running all of the strand jacks, which is controlling the lifts the entire time. The computer knows what each corner is picking up, the weight, the speeds, the deflections, how fast they’re moving—we know everything about the move. We can actually control how much each corner is picking up and it tells us. The whole lifting process, sliding sideways and lowering down was done by hydraulics, controlled by the computer. The accuracy that each corner is picking up is within two kilonewtons (500 pounds).”

The bridge weighed 330 tons and measured 150 feet long, 21 feet tall and 18 feet wide.

“The gussets had to be removed before lowering,” he said. “When the bridge was actually hanging in the top position, all the bolts were removed and the gussets were removed. That’s the part that took longer than expected. We did do it within the allotted five hours, 40 minutes, but we could have done it a fair bit quicker. What was supposed to happen was that CN and our crew were to work together to take those brackets off. We were told not to worry about putting the bolts in since it would done once the bridge was lowered down. We had leftover time, and we decided to finish the whole thing while it was still suspended. We still finished within the time period and got some extra done for the customer.”

Tucker noted that the deck and span are all in place, but there’s still quite a bit of work that needs to be done to prepare the third-track span for trains.

“We still need to configure the retaining walls, do the grading, prepare the approaches for the bridge, waterproof the deck and put the signals and track into place,” he said. “Then it will be ready to go.”