Across New Mexico, approximately 5% of National Highway System (NHS) bridges have come to the end of their design life, with many of them deemed structurally or functionally deficient. To remedy the situation, the state is replacing several NHS and non-NHS bridges a year. To minimize impact on traffic caused by this construction, they are increasingly relying on accelerated bridge construction (ABC) methods to deliver these projects quickly and efficiently.
Such was the case for the replacement of the FR 2142 five-span bridge Airport Interchange in Las Vegas, N.Mex.. Because of its importance to local businesses and residents, disruption had to be kept to a minimum, says Tom Cartner, with New Mexico Department of Transportation. The local transportation district also wanted to maintain the existing alignment and profile grade to eliminate realigning or reconstructing approach roadways.
The designers of this ABC bridge went with a precast concrete system to achieve these goals. “Using precast, members provided the rapid construction needed without resorting to more expensive and specialized ABC methods,” Cartner says. “The use of precast also allowed close dimensional tolerances and excellent finish quality despite the construction time constraints.”
The biggest challenges the designers faced on this project were designing the abutment foundations and completing the project within the limited timeline allotted for interstate detours. The project required reusing the exiting alignment and profile grade, which required constructing the new foundations under the existing bridge while still in service, says Fernando Quiroga, president of Quiroga Pfeiffer Engineering Corporation. “There was not enough room for spread footings at the abutments and not enough vertical clearance for typical driven pile or drilled shaft construction,” he says.
As soon as the existing bridge spans were demolished, the abutment and precast pier caps were used to bring the substructure up to final girder seat elevations; then reinforcing bar splices were used to quickly connect precast concrete elements with their supports. All precast concrete members were fabricated, inspected, and approved before the start of the time-limited bridge removal and replacement operations, Quiroga says. “It is unlikely the same level of quality control could have been met with traditional field construction methods under the project time constraints.”
As a result of these design choices, the demolition and construction of the new superstructure was completed in just one week. During that time, interstate traffic was detoured alternately to lanes opposite the span under construction, allowing safe removal of existing spans and placement of new concrete elements. The new bridge not only met all of the schedule and budget considerations, but it also delivered a sleek modern design with clean lines and warm earth tones that elegantly complement the desert landscape.
“This project received very positive comments from those involved, Quiroga says. “The precast members made superstructure construction a relatively fast and simple assembly operation.”