Precast manufacturing clears away multiple construction headaches on a major infrastructure project in Suffolk, Va.
By Bridget McCrea
When the City of Suffolk, Va., set out to replace two of the roughly 15 bridge structures that had been classified as “structurally deficient and functionally obsolete,” the municipality didn’t realize what it was getting into.
“When we first got started, we figured it would be a breeze,” said Antonio Jordan, operations manager for the city’s public works department. “After all, these were just small, puddle-hopper-type bridges. We were going to get in there, do what we needed to do, and get out.”
It didn’t take long for reality to hit, and for the project to become much more complicated than the city could have predicted. Situated about 1.5 miles apart, the two bridges serve as vital conduits for area residents. And because they both spanned water, unpredictable elements like bad weather and some environmental concerns would force the city to rethink its original plans for replacing the structures.
Initially, the city specified cast-in-place concrete structures to replace the antiquated bridges, which Jordan said were built in the 1950s. With about 130 total bridges located in Suffolk, the two in question both had weight restrictions and were constructed with the goal of bridging a swampy wetlands area. But as those bridges aged, they fell out of code. Repairing them started to get costly, according to Jordan, so the city knew that replacement was in order.
“Both bridges are located in rural settings, so we had to worry about fire and rescue, school buses and other types of transit being able to get in and out of the areas that are served by those structures,” said Jordan, whose team wanted the replacement process to take no more than six to nine months, max.
Due to that time constraint, and the fact that cast-in-place could require extra permitting time (namely due to environmental/wetlands considerations), the city began to explore precast concrete structures as a viable option.
“We felt like we could really speed up the design process and get into the construction phase faster by switching from a traditional box culvert to a 3-sided precast one,” said Jordan, who worked with engineering firm Parsons Brinckerhoff during the process. “That way, we wouldn’t have to disturb the creek bed and hurt our chances of getting the environmental permit as fast as we did.”
Battling the elements
Using precast elements also allowed the contractor, Precon Marine of Chesapeake, Va., to work on the two bridges simultaneously. For example, just two months into the project, the company was able to finish up with some of its equipment on the first bridge, and then move that equipment 1.5 miles down the road and use it on the other bridge.
Bryan Ellis, Precon Marine’s project manager, said it’s getting fairly common to see older infrastructure projects replaced with precast concrete structures. He said the precaster, Tindall Corp. of Spartanburg, S.C., provided a unique culvert design for the bridges that incorporated a 3-sided culvert with abutments on either side and a center pier.
“Tindall helped us convince the city the right way to do that was to also make their foundation pieces precast,” recalled Ellis, noting the original plans called for a 3-sided precast culvert to sit on top of a cast-in-place concrete footing. “With the schedule we were working on, the weather conditions, and other variables, we felt precast would save everyone time and money.”
An all-in-one approach
Working with Precon Marine, Tindall Corp. provided a complete precast solution for Suffolk’s bridge projects. Tindall engineered, manufactured and delivered flat-top, three-sided bridge pieces, wing walls, headwalls and precast foundations. One bridge featured two three-sided bridge sections with a combined span of 52 feet, and the other was a single three-sided structure spanning 30 feet.
The all-in precast approach, including the foundations, enabled the fast installation times the city wanted. Using an “emulative design” process, Tindall precasted the footings to closely mimic the original design.
“We could have made the footings smaller, but time just didn’t allow for it,” said Barry Phillips, sales manager for Tindall’s Utility Division. “So, we expedited the process by offering the exactly what it already had in its plans.”
Phillips said the project kicked off with the precaster working with Parsons Brinckerhoff and Precon Marine during the bidding process. The project was unique in that it would involve a total precast solution versus one that simply incorporated various types of precast pieces. Phillips said one of the main reasons for using precast was the area’s weather conditions, which prohibited the wetlands from being drained enough to be able to pour the concrete footings.
“We offered them a solution to precast the footings with stem walls,” he explained. “That way, they were able to install the footings without having to try to pump it down or build a diversion in the area around the bridge.”
It never rains in a precast plant
Randy Price, Tindall’s technical sales rep, said one of the biggest advantages of using precast concrete for the two Suffolk bridges was its environmentally friendly qualities.
“We were trying to mitigate wetlands, where you always want to have minimal disturbance,” Price said. “So, instead of the typical normal bridge – with columns extending downward and interrupting the beautiful fish and crawfish in that gorgeous creek – this structure just spans the water.”
Making precast even more attractive in this situation was the fact that the components could be manufactured in advance, and in a temperature- and quality-controlled plant setting.
“When you’re getting bad weather and flooding that’s trying to raise a creek, you can’t cast in place, but it never rains under the roof of a precast plant,” Price pointed out.
As he ran his finger down the list of city bridges that need to be replaced or repaired over the next few years, Jordan said the success of these two projects will surely have an impact on Suffolk’s material of choice for upcoming replacements.
“We do have plans to do replacement of some of the bridges that are similar in size and in a rural setting just like these two were, and I’ve been instructing my design engineers to push wherever we can to utilize these types of precast structures,” Jordan said.
Bridget McCrea is a freelance writer who covers manufacturing, industry and technology. She is a winner of the Florida Magazine Association’s Gold Award for best trade-technical statewide.