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Implosion Opens Path for New Bridge

Tuesday, January 5, 2016

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Pittsburgh, known by many as the City of Bridges for the sheer number it contains, said farewell to one 94-year-old structure with a much-anticipated implosion on Dec. 28.

The Greenfield Bridge, which connected two city neighborhoods by crossing over major artery Interstate 376, closed in October to allow for two months’ worth of dismantling work by Mosites Heavy Construction prior to the December implosion.

Wikimedia Commons
By Doug Kerr / CC BY-SA 2.0 via Wikimedia Commons?

Pittsburgh's Greenfield Bridge, a symbol of the state of the nation's infrastructure spending, was imploded Dec. 28 to make way for a new bridge.

Demolition was just part of the $17.5 million reconstruction project. Mosites will build a new span in its place, which is slated to open in May 2017.

A Symbol of Deficiency

The Greenfield Bridge was not just meaningful to Pittsburgh’s locals. Viewers of 60 Minutes may remember it being called out as a symbol of the state of the nation’s infrastructure in a 2014 story.

Filming from a helicopter overhead, reporter Steve Kroft used it as an example of what happens when there isn’t enough funding to keep up with repair of structurally deficient bridges.

In addition to black netting wrapped around sections of the concrete arch to contain crumbling debris, the camera showed the temporary solution in place for this particular bridge: another smaller bridge built underneath to catch falling concrete before it could hit the heavily travelled roadway below.

This protective element of the secondary bridge also became an important part of last month’s demolition.

Bringing It Down

According to the Pittsburgh Post-Gazette, 1,400 pounds of explosives were used to bring the bridge down in just a few seconds. Dykon Explosives Demolition Corp. and Kesco Inc. worked with Mosites on this aspect of the project.

To protect the roadway where the structures would collapse, 4,000 cubic yards of dirt was mounded across the road surface to cushion the blow. Additionally, the temporary “bridge under the bridge” sustained part of the impact from the demolition, providing additional protection.

Demolition crews called the event “near-perfect,” the paper said, citing several concrete pillars on a hillside to the left in the video footage that didn’t come down with the controlled blasts.

Demolition crews called the event “near-perfect,” the paper said, citing several concrete pillars on a hillside to the left in the video footage that didn’t come down with the controlled blasts. Those pillars, however, were able to be pushed over with a bucket excavator later that day.

Just three days later, construction crews had removed all of the debris and dirt and were able to reopen the road to Pittsburgh drivers for New Year’s holiday travel.

Starting from the Ground Up

Originally built in 1922 to replace an earlier 1909 wooden structure, the span was one of seven concrete arch bridges constructed in the city at the time, the Pittsburgh Tribune-Review reported prior to the bridge’s closing.

The last major rehabilitation to the bridge occurred in the 1980s.

In planning with the city's Department of Public Works for the past 16 years, a number of options for reconstruction were considered, Pat Hassett, the city’s assistant public works director, told the Post-Gazette in October.

However, rehabilitation of the existing structure would have increased the bridge’s lifespan only by 30 years and cost about the same as replacement, he said.

The new bridge will be constructed with a green steel arch rather than concrete; the concrete used in other areas will be graffiti-proof, the paper said. Decorative elements that hearken back to the original structure—urns and ornamental lampposts—will be included in the new build.

It will allow for travel of three lanes of traffic, a protected bike lane and a larger 10-foot sidewalk.

Reuse and Recycle

This isn’t the end for the old Greenfield Bridge, however. During cleanup efforts, materials were sorted for future use, the Post-Gazette reported.

Of the 2,000 cubic yards of weathered concrete that came down, the pieces are expected to be ground down and reused as a gravel material, possibly as fill around the new bridge’s abutments.

The steel was hauled away to Josh Steel Co., a scrap processor in nearby Braddock. From there, the recycled steel could find new life in cars, appliances and industrial pipes, James Joshowitz, company officer at Josh Steel, told the paper.

Even the dirt brought in to cushion the impact of the implosion is expected to be repurposed as a maintenance platform along the roadway under the new structure.

   

Tagged categories: Asia Pacific; Bridge Piles; Bridges; Concrete; Demolition; EMEA (Europe, Middle East and Africa); Latin America; North America; Program/Project Management; Steel

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