By Angus W. Stocking
For years, accelerated bridge construction has enabled DOTs to accomplish more in less time and for less money. Now, some DOTs feel that the experimental phase of precast concrete use in ABC is coming to an end. Lessons have been learned and it’s time to apply those lessons more routinely on more projects.
Pilot phase complete
“The current state of accelerated bridge construction, and particularly precast bridge elements, is that a lot of pilot projects have been completed by owner agencies, mostly due to programs developed by the FHWA,” said Bill Oliva, P.E., chief of structures development for the Wisconsin Department of Transportation’s Bureau of Structures. “And a lot of these projects have been custom, experimental, or stand-alone – with all the extra costs that implies. Now, we’ve learned a lot and have established that this is not a passing thing – the use of precast elements in bridge construction is a new paradigm.”
Specifically, Oliva said WisDOT is able to simplify and standardize the types of elements needed in bridge construction and is reaching out to contractors and the precast industry to share what’s been learned.
“That should raise the comfort level in the industry and encourage longer-term investments in reusable forms and other equipment and techniques,” Oliva said. “Ultimately, there’s no reason precast bridge elements can’t achieve cost parity with other bridge construction methods.”
Oliva hopes that agencies and contractors will work together to create simpler, broader standards for precast bridge components. Then, contractors and precast plants will make investments and workflow adjustments that take advantage of the standardization. The costs and timelines of bridge construction will both be reduced as a result.
Wieser Concrete Products is one of several Wisconsin plants now certified to produce precast components for WisDOT. Certification means that components manufactured by Wieser, like vaults and catch basins, don’t require individual inspection during casting. Executive Vice President Mark Wieser agrees with Oliva.
“Without standardization, the use of precast requires earlier involvement of precast subcontractors during the design phase and that obviously adds expense,” Wieser said. “As bridge elements do become standard, we can start to build forms that will be more efficient to use and that will last a lifetime. That’s just one factor that will drive costs down.”
Much of the experimentation in ABC, at WisDOT and nationwide, has been encouraged and partially funded by the Transportation Research Board’s second Strategic Highway Research Program, which was created to find strategic solutions to three national transportation challenges: improving highway safety, reducing congestion, and improving methods for renewing roads and bridges.
“With each project we’ve undertaken, we’ve debriefed project staff from designers to fabricators and contractors to see what can be better,” Oliva said. “And we’ll also show up at stakeholder conferences like the Wisconsin Transportation Builder Association and the American Council of Engineering Companies to show what we’ve been doing. We talk about what we’ve learned and how we want to go forward.”
The SHRP was put to good use in Wisconsin. On just one ongoing project, Interstate 39/90 between Dane County and Illinois, four SHRP bridge projects have already been completed and one more will be completed in 2016. Much was learned, including a measure of precast’s potential in ABC.
“There’s a total of 62 bridges on this project, and at least 50 of them are suitable for the use of precast,” Oliva said. “In fact, contractors are able to implement precast now if that’s what’s they feel is appropriate, and I expect many to take advantage of that option.”
Standardization, simplification and interchangeability
To increase use of precast bridge elements and bring down costs, WisDOT has identified key concepts that work together: standardization, simplification and interchangeability.
“With our precast elements, what we’ve chosen to do is to make them simpler and to standardize them,” Oliva said. “The goal is to make them interchangeable with cast-in-place elements. If we can do that well, agencies and owners will be able to switch from one to another at any point in the project, from design to construction.”
As precast components become simpler, more standardized and interchangeable with cast-in-place, tremendous flexibility will be introduced for agencies and contractors. For example, if the construction timeline is threatened by inclement weather, the contractor will have the option of replacing cast-in-place elements with precast elements, without redesign and without change orders.
“It will require notification, and our concurrence, of course,” Oliva points out. “But why wouldn’t we do that?”
Likewise, if WisDOT finds that lane closures are having unexpected effects on congestion and traffic, they’ll have the option of imposing precast use mid-project, to shorten construction time. Oliva sees this as a tool for managing construction risk.
“I spent a decade as a project development supervisor, and it was clear to me that we needed something like this,” Oliva said. “When dealing with unexpected issues that affect schedule, safety and traffic control, an option like this has tremendous utility. There are many cases where interchangeability will make a difference.
“Here in Wisconsin, just having a way to accelerate schedules to beat the onset of winter and have full operation before snow falls will be something we use all the time.”
Wieser doesn’t think that ideas like this will be limited to use in Wisconsin.
“As a rule, WisDOT is very good at working with contractors and suppliers, so it makes sense that the use of precast bridge elements is off to a good start here,” Wieser said. “But as other DOTs see the durability and ease of use, they’ll adopt these methods as well. It’s a new concept, but everyone values speed and keeping roads open.”
Oliva agrees. “Right now, most states are developing their own standards for ABC and precast,” he said. “But the FHWA has produced good guidelines and detailed documents too, and I think that we will start to see some national standards develop. It would be nice if that happens, and good for contractors.”
For example, if Illinois plants could confidently develop forms for elements used there and in Wisconsin, that would bring costs down for projects in southern Wisconsin, he said.
Tom Heraty, vice president of sales and engineering at Utility Concrete Products in Morris, Ill., said precast concrete in ABC is progressing in Illinois due to state officials embracing innovative ideas. For this reason, Illinois Department of Transportation consultants and contractors contacted the company to learn more about precast concrete products. The relationship formed with IDOT led to Utility Concrete receiving a call to manufacture precast bridge approach slabs for an Illinois Tollway ABC project, a product that had always been cast-in-place in Illinois. He said for precasters that are already manufacturing modular products and are interested in manufacturing ABC precast products, the best place to start is to contact state officials and decision makers directly.
“We got involved by having a good reputation and either talking to IDOT consultants or getting involved with trade groups,” Heraty said. “We also prepare ourselves by reading publications to be aware of the latest technologies available.”
He said most transportation agencies, like IDOT, are choosing precast concrete in construction designs since they are seeing not only the cost savings as a result, but safety and traffic savings as well.
Always an option
When asked if there are bridge projects where the use of precast elements will not be appropriate, Oliva said, “There may be some, but I can’t think of any off the top of my head. We’ve done the research now, and it suggests that if we successfully create common standards, and work with the industry, we’ll start seeing routine, cost-effective use of precast.”
Oliva does think there will be a clear progression in implementation of standard elements; first substructure bridge pieces, then abutments, then possibly deck panels. Precast may even have a role in bridge repair and rehabilitation. WisDOT is currently looking at substructure elements and precast deck panels as a possibility for future projects.
“We’ve done some work with deck panels in the past, and there are factors to address, but I think we’ll get there,” he said.
The material of choice
It’s an exciting time for agencies and contractors. ABC with precast elements, once considered a new – albeit promising – technology appears to have matured and is on the verge of general acceptance. Many successful pilot projects have been completed, the concept has been proven effective and broad standards are emerging. The effect on ABC is likely to be profound.
“I think it’s inevitable that costs will come down and achieve parity with cast-in-place,” Oliva said. “Or even better than that, precast concrete girders are much cheaper than steel girders now, and there’s no reason the same market forces won’t have the same effect on other bridge components. Concrete and precast is not right for every situation, but it will become predominant. I believe it will be the default.”
Now, as precast bridge construction becomes standardized and more flexible, actually reducing construction risks, it seems likely that agencies and builders will work together to drive investment and achieve massive economies of scale that drive down costs. That will make precast elements in ABC faster, better and more cost-efficient. And when that happens, the world changes.
Angus W. Stocking, L.S,. is a licensed land surveyor who has been writing about infrastructure since 2002.
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