Today’s round of questions, my smart-aleck replies and the real answers:
Question: I would really like to hear more about the history and progress of the very lengthy task of widening I-26. I’m particularly interested in the engineering marvel being instituted to extend the Blue Ridge Parkway over the interstate. I think some math is being used, right?
My answer: I keep waiting for these DOT engineers to tap into my phenomenal reserve of math knowledge to get this project finished. Maybe they were turned off a bit when I suggested this new cantilevered bridge was “just like a big ol’ seesaw, right?” Trust me, you want to rely on a guy with an English degree for this kind of building project.
Real answer: The North Carolina Department of Transportation held a press gaggle and tour of the new Blue Ridge Parkway bridge project Monday. This type of bridge uses a balanced cantilever method, and yes indeed it requires a lot of math.
In a nutshell, it’s being built piece by concrete piece, with those pieces slowly extending outward from a concrete pier. So counterweights and math calculations are pretty crucial.
Luke Middleton, a resident engineer for the NCDOT in Buncombe County, works for RK&K, a contractor on the I-26 project. VSL, a giant international company that specializes in bridge construction, is the main contractor on the new Blue Ridge Parkway bridge over I-26, which has a total price tag of $14.5 million.
The bridge will be 605 feet (about 184 meters) long when completed, with two travel lanes and a sidewalk. The width is 36 feet (11 meters), and the roadway has a 6-degree slope to it, as it is in a curve on the Parkway.
The bottom of the new bridge will be 85 to 90 feet (26 meters) above the I-26 roadway, the top 105 to 115 feet (32 to 35 meters). It will have a pedestrian sidewalk on the north side.
What makes this bridge unique is that all of its 76 pieces were pre-cast in Wilmington, N.C., starting in April 2021. Of the pieces, 62 are for the bridge superstructure and 14 for the two main piers.
The construction so far is all on the east side pier. These pieces fit together perfectly, like giant building blocks, and they are sealed with an epoxy to keep water out.
A series of steel cables, called tendons, run through the bridge on the top and bottom, adding support. The bridge will have 18 tendons on the top, 12 on the bottom, running the length of the structure.
Workers “stress” the tendons on each section, essentially tightening them up. The bridge segments are hollow inside, and they come with “handling bars” inside — sort of large, threaded bolts — that workers can use to pull the segment tight. The bars are removed once the bridge is in place.
The tensioning will often squeeze out some of the epoxy, which will be removed.
“Completion of the east side of the bridge is scheduled to be done in January-March,” Middleton said, noting that winter weather plays a key role in that time frame. Already, they’ve encountered delays because the epoxy takes longer to dry in colder weather.
This is all part of the $531 million widening project of I-26 spanning 17 miles from Brevard Road in Buncombe County to U.S. 64 in Henderson County. The project, which started in October 2019, will expand the interstate to eight lanes for much of that distance, and it should finish in 2024.
Eugene McGirt, principal bridge inspector for the DOT, said, “The contractor is trying to get 20-40-degree epoxy approved,” and if approved and delivered, that will speed the project considerably. As the name implies, that epoxy can be used at lower temperatures.
Motorists have likely spotted an enormous crane on site that is being used to lift the individual segments — which weigh about 70 tons — into place. A blue “segment lifter” sits atop the bridge pier, and it will be used to put pieces in place and serve as part of a counterbalance system.
“We had to order a couple more pieces for the segment lifter,” Middleton said. “We anticipate using it in early December.”
With the cantilever construction, as a piece is added to one side, it has to be counterbalanced on the other side. The first segment was delivered Sept. 14 and lifted onto the bridge.
“Windy days can dictate when we put in a piece,” Middleton said.
Workers access the top of the bridge via a scaffolding stairway on the north side of the pier, or by a man lift.
Four segments on each side of the pier should be in place in December. Once the east side of the bridge is finished, the DOT will have to switch traffic on I-26 to the west bound alignment so workers can install the other half of the bridge.
“Construction of the bridge will never be over live traffic,” DOT spokesperson David Uchiyama said.
Middleton said a total completion date on the bridge is tough to give, because of the weather, “but it could get done by the end of the summer, early fall.” He stressed that’s a very rough estimate.
The balanced cantilever method results in a stronger bridge, Middleton said, noting that the existing Blue Ridge Parkway Bridge likely has concrete rated for 4,500 pounds per square inch pressure.
“This bridge is 6,000 PSI, and in some places it’s 10,000 PSI,” Middleton said.
The bridge will sit on two concrete piers and two bridge abutments on either side of the roadway.
The precast concrete segments have steel rebar reinforcement running throughout.
“It’s supposed to last longer and have more strength,” Middleton said.
While they’ve run into some delays because of the epoxy and cold weather, it is quicker to erect this kind of bridge than a traditional poured concrete structure.
“I would say it’s much faster, and that’s because all of this is finished product,” said McGirt, who’s been working in bridge construction, including balanced cantilever bridges, since the 1970s. “It’s hard to say, but I would say it’s several months (faster).”
Once the new bridge is completed, the old Blue Ridge Parkway bridge will be removed. Middleton did not know what technique will be used for demolition, but much to my disappointment he said he seriously doubts it’ll be blown up.
Some of the girders to the existing bridge, which is still in use, run continuously, making it difficult to blow up, Middleton said.
My offer still stands on some math help, and explosions. I calculate it would take at least 10,000 pounds of dynamite to blow that sucker to smithereens.
Got a question? Reach out to Asheville Watchdog Answer Man John Boyle at (828) 337-0941 or email him at firstname.lastname@example.org