Iowa Department of Transportation
Iowa Highway Research Board
Brent Pharesbphares@iastate.edu email >
Bridge Research Engineer
About the research
Longitudinal joints are thought to provide relief from expansion and contraction of the bridge deck resulting from temperature change, shrinkage, and live loads. Historically, however, these joints have been known to leak, allowing chloride-laden water to reach the bottom of the deck overhang and even the exterior girders.
One of the primary conclusions from the previous Phase I project was that the development of cracking in bridge decks appears to be less dependent on the total width of the deck and more dependent on restraint of the abutment to temperature changes and, in particular, temperature gradients. Based on the results of that research, a 115 ft long, 228 ft wide, bridge in Black Hawk County, Iowa was selected and designed to incorporate a thermal isolation barrier.
The objective of this research was to follow and document the design, construction, and performance of the bridge in Black Hawk County with a specific focus on the success of the deck crack mitigation efforts. To achieve this objective, the newly constructed bridge on Viking Road over IA 58 was selected for this study.
A nearly two-year-long monitoring period enhanced by multiple bridge inspections was conducted. In addition, an analytical study was conducted to investigate the efficacy of the isolation barrier on resisting the cracking at the end of the deck for an integral abutment bridge.
The results confirmed the findings from the Phase I research that development of cracking in bridge decks seems less dependent on the total width of the deck. The finite element model results indicated the maximum deck strain to be 46% greater without the effects of the thermal isolation barrier. This indicated that, without the thermal isolation barrier, the Viking Road Bridge could see cracking at the end of its deck.
The researchers recommend the use of a thermal isolation barrier between the abutment and backfill soils for wide integral abutment bridges as one way to lengthen the service life of these bridge decks while reducing maintenance, rehabilitation, and/or replacement costs as well.