Replacing bridge? It’s a big job
This isn’t a task for the faint of heart: moving a pair of 70foot-long, 270-ton bridge spans more than 600 feet and placing them above a highway.
But that’s exactly what a crew will do later this month to replace the Shaler Street Bridge that crosses Route 19/51 near the West End Bridge in Pittsburgh’s Duquesne Heights neighborhood. This will be the first time the process is used in Pennsylvania and is part of a $14.3 million contract with Swank Construction Co.
The project also includes replacing the asphalt surface of the highway with concrete and lowering the ramp to the Parkway West by about 3 feet to prevent trucks from crashing into another overhead bridge there.
“There’s nothing exotic about what we’re building here,” Jason Zang said last week
as he stood in a parking lot beside the highway at Minnotte Manufacturing Corp., where crews have been building the bridge spans for months. Mr. Zang is assistant district executive for construction for the Pennsylvania Department of Transportation’s District 11.
“We’re just using a very specialized piece of equipment to move it into place.”
That equipment is called a self-propelled modular transport supplied by the Torontobased firm Mammoet. The system uses a series of small hydraulic trailers, each capable of holding 30 metric tons, to lift and move the bridge components into place.
Mr. Zang said the agency had been looking for a project to use the process known as accelerated bridge replacement for several years. Shaler Street offered the right components: a relatively short bridge that’s not on a major highway and has a nearby staging area to assemble the spans before moving them into place.
“I’d say we try to be innovative,” said Mr. Zang, who said it wasn’t difficult to convince department heads in Harrisburg to try the concept. “We may not be the first to think of something, but we’re willing to try new things.
“There are limited areas where this would work, too. We’re not going to try something like this for the first time on the Parkway East.”
In 2016, PennDOT used precast concrete pieces lifted by a crane to replace a small bridge on Route 30 in East Pittsburgh over one weekend, and the Pennsylvania Turnpike built a new bridge beside an existing one in Beaver County, tore down the old one and slid the new one into place. But this is the first time in the state that huge bridge spans have been built off-site and carried into place.
Mr. Zang said using this process is more expensive — he wasn’t sure how much more — but the key factor is that replacing the bridge in this manner will cause far less disruption to traffic. Normal construction would have closed the bridge for six to eight months, inconveniencing about 4,750 motorists who use it every day, and required overnight and possibly weekend closures on the highway for overhead work on the bridge.
The highway carries about 28,000 vehicles daily.
But using this method, crews closed the highway to remove the bridge the weekend of Sept. 7. The highway will be closed again when the spans are scheduled to be moved into place Oct. 31-Nov. 1, and the new bridge should be open two or three weeks later.
“It’s basically two closures,” said Norm Arlet, overseeing the project as a supervisor for SAI Consulting Engineers. “It’s lessening the inconvenience to the public greatly.”
Although Mr. Zang said the finished spans are like most others, they were assembled in a different order and have one different component: beveled steel plates on the underneath side where the transports will lift them. The spans were constructed off the ground on platforms at the exact angles they will have when they are in place.
In traditional construction, crews can compensate if something comes up short. That’s not true with pre-assembled spans, where concrete components are already in place, Mr. Zang said.
“There’s a lot more attention to dimensions and elevation to make sure it fits together right,” he said. “With this, once the concrete cures, it has to fit.”
Cary Basinger, project manager with Swank, said the company, PennDOT and Mammoet still are deciding the exact path they will follow to put the new bridge in place. They could build a temporary ramp across the highway median adjacent to the bridge or go a short distance away where the two sides of the road are almost parallel.
Either way, Mr. Basinger said he is ready for the move.
“We’ve been talking about it for some time,” he said. “I think [Swank enjoys ] a challenge. We look forward to something new and unique. It will be exciting to see it happen.”