If there is a structure that demonstrates the exacting preciseness that B.C.’s construction industry can achieve, it is the $4.3 million Salton Road pedestrian and cycle bridge.
When the 79-metre (260-foot) steel bridge was craned into place over a shutdown section of the Trans-Canada Highway during an October 2018 night, it required shear key ends to line up exactly so the span would seat in the bank abutments.
“The tolerance on the shear key ends was three millimetres (one-eighth of an inch),” said Aidan Connell, Graham Infrastructure LP’s project manager during the construction and placement of the bridge. Once the shear key ends were in place, the bridge ends could be locked in place and the final fastening completed.
The design-build contract for the bridge, which connects the University of the Fraser Valley to downtown Abbotsford, has earned both Graham and Marcon Metalfab Vancouver Regional Construction Association silver awards of excellence. Graham received its award in the category of projects valued up to $15 million by a general contractor. Marcon Metalfab, which fabricated the components of the bridge, received its silver award in the category of suppliers and manufacturers.
“The challenge was the measuring and the measurement checks,” said Marcon’s project manager Farzan Farzaneh as the work had to be precise to ensure that the assembled bridge components fit perfectly with the drawings.
Adding to the challenge was the fact the drawings were only 30 per cent complete when the project started in January 2018, the contract award date. Marcon delivered the first bridge components April and the last in December.
In order to fast-track the fabrication, Marcon broke this into 19 different sections. Before the project drawings were complete, the company would go through a total of 458 sets of drawings for the combined bridge components and spend a total of 4,298 hours on the fabrication.
The bridge’s large arches are steel pipe. When the project was first considered in 2017, there was no problem in sourcing materials. But steel prices soared and suppliers cut their inventories. The needed pipe was nowhere to be found in North America. Marcon only was able to find two replacement pipes; one proved superior. The task became estimating before the final drawings were completed how much of the 24-inch-diameter pipe was needed and how much needed to be factored in as a margin for error. The company took risks. It sent the pipe for rolling (curving) before the shop drawings were complete as rolling can take three to four weeks.
In addition, all the bridge components had to be delivered in a sequence as Graham was assembling the bridge near the site. “All the structural members, the floor beams, the arches, abutment structural boxes, the road hangers and the shear keys were all part of a critical path,” Farzaneh said. Any problems would impact the project.
The bridge components were trucked to the Graham assembly site, which was the green space or median between lanes of the Trans-Canada Highway, known as Highway 1 in the western provinces. The long, 24-inch-diameter rolled arches were shipped in five segments for each arch. As bridge pieces arrived, they were propped into place and welded onto the structure.
“One of the primary challenges was working on the busy highway’s median,” said Connell. The chosen site was close to where a crane would eventually lift the bridge into place connecting the structure to the south and north sides of the highway. The 30-metre-wide and 46-metre-long site provided space for storage containers, crews, lay-down area, and a 120-tonne crane. The area between the freeway lanes is a V-shaped gulley and the work space had to be raised to a flat surface before any work could begin.
There was also the consideration for traffic. The site of a bridge, with a high point of 10 metres that was under construction on the median was a curiosity to drivers creating a safety issue for both the work crews and motors.
“We put up a privacy screen and large roadside barriers on the edge of the median to prevent traffic from veering onto the median and also to protect workers,” said Connell, but as the bridge progressed it became more difficult to hide.
On the evening and morning of October 20 and 21, the built-out bridge was ready to lift.
“We got the green light to shut down the highway and the crane was in position,” he said as it had lifted the structure a foot off the ground preparing for the final heft. The bridge would turn from an east-west position to a north-south position and then come to rest on the abutments.
The lift followed a thorough engineered lift plan. “When you lift something off the ground it behaves differently,” said Connell. Two factors had to be reconciled. The first was the hanger rods. The lifting tension could compress and break the hanger rods. The crew identified which of the hanger rods were susceptible, and then, loosened them to reduce tension. The second factor was that any mid-point lift caused a shortening of the bridge, a critical point as it had to land exactly on the shear key points for final fastening.
“We dropped it down on one side first,” said Connell. As the weight of the bridge was lowered onto the abutment, the sag in the bridge relaxed and it was able to drop down into the other bank abutment hitting the second set of shear keys.
Associated Engineering’s Nik Cuperlovic, the engineer of record, said the bridge is unusual as it is removed from the normal straight utility bridge. “We wanted to build a beautiful bridge,” he said. The design of the four-metre-wide, painted steel bridge features graceful carved arches, LED lighting, platforms and benches at the top of the 218-metre approach ramps and at switchbacks. The main span’s fence has trapezoidal panels and fence post aligned with the bridge hangers for a visual effect. The art of Brent Bukowski, a collage of rolling bicycle wheels, entitled The Hop Across, was installed on the bridge.
Cuperlovic said the bridge was designed to accommodate the lift. The arch ribs were able to be lifted with hangers, tie beams and deck using four lifting lines attached at quarter-points of the arch. The total weight of the steel structure to be lifted was just under 80 tonnes. The concrete deck was later cast on galvanized steel, stay-in-place forms, which involved no traffic closures.
Throughout the project, cost was a consideration. Cuperlovic said the original plans called for a span supported by a pier in the highway median but the design team felt that a free-standing single span was more appealing and would require less maintenance. The higher cost of providing the superstructure was offset by the need for the construction of a mid-span pier.
When Connell looks back at the project, he maintains it took a strong team effort to achieve the exacting standards required. “It was really a lot of people coming together to make it happen and a successful endeavour,” he said.
Recent Comments
comments for this post are closed