Speeding Up Time

The multiple values of accelerated bridge replacement

A section of the I-15 Prairie Crossing superstructure is moved toward placement in Utah in October, 2009.

The cost of user delays in an era of unbridled traffic congestion is driving today’s fast-paced bridge erection technology, and it’s being encouraged by the Federal Highway Administration (FHWA) in partnership with active state DOTs.

Those state DOTs are accelerating bridge replacement via use of prefabricated bridge components that are either placed on site, or assembled on site into a superstructure and then installed in one swift action.

The fast-tracking of bridge replacement via prefab sections is only one of a series of major advancements happening in bridge technology. Others include:

* Fiber-reinforced polymer (FRP) composites continue their inroads into bridge design, at the expense of precast concrete and lightweight aggregate. Three new design themes emerged in 2011 as focus areas for the American Association of State Highway and Transportation Officials (AASHTO) Subcommittee on Bridges and Structures: rigidified FRP tube arches, hybrid composite beams, and reinforced thermoplastics technology.

* The growing acceptance of self-consolidating concrete (SCC) is making erection of conventional precast, post-tensioned structures – and those using FRP components – easier as they greatly reduce the need to vibrate concrete mixes into complex steel reinforcement, either in-plant for precast, or on site for poured-in-place.

* Both precast and cast-in-place concrete proponents look forward to concrete-grade coal fly ash escaping designation as a “hazardous waste” as sought by the Environmental Protection Agency (EPA). The classification of fly ash as hazardous waste could introduce chaos into the production of high-performance concrete for bridges.

Every Day Counts

Fast-paced bridge replacement using precast components is a high priority for FHWA and is a critical part of its Every Day Counts (EDC) initiative.

“Every Day Counts reflects a new sense of urgency we bring to our work,” said FHWA Deputy Administrator Greg Nadeau at the second International Warm Mix Conference in St. Louis in October (warm mix asphalt also is being promoted through the EDC program).

EDC aims to make highway and bridge building more efficient and effective, Nadeau said. “FHWA doesn’t deliver projects; we support our partners who support a more effective delivery of the federal-aid highway program.”

That includes fast replacement of bridges by use of what FHWA calls prefabricated bridge elements and systems (PBES) technology, he said. “As a result, bridges are built faster, and with much less disruption to the traveling public and, importantly, to commerce,” Nadeau said. “These techniques and technologies are going to have to be deployed, especially in areas that are experiencing significant congestion. We want to rapidly deploy technology that makes sense.”

With prefabricated bridge elements and systems, many time-consuming construction tasks no longer need to be done sequentially in work zones, FHWA says.

These PBES superstructures are assembled adjacent to or away from the jobsite to limit construction in the right-of-way, as is the conventional practice. “An old bridge can be demolished, while the new bridge elements are built at the same time offsite, under controlled conditions, then brought to the project location ready to erect,” FHWA says.