About the research
Since the early 2000s, several federal programs have existed to provide bridge owners with funding to cover “delta” costs associated with implementing new, emerging, and innovative bridge technologies. While these programs have generally included an evaluation component, there generally has not been a concerted effort to track the performance of these innovative bridges following the completion of the initial project.
The goal of this work was to conduct field reviews of the condition and performance of several innovative bridge concepts constructed in Wisconsin. The completion of this work was to provide a much needed review of the performance of these bridge as they had been in service for several years.
This report documents the condition of 11 innovative bridges or innovative bridge features in Wisconsin. The bridges have innovative technologies consisting of the following: inverted T-beams, exodermic deck, geosynthetic-reinforced soil (GRS) abutments, fiber-reinforced polymer (FRP) components, steel free deck, bi-directional post-tensioning, stainless steel reinforcement, and precast substructure components. Collectively, these innovations represent departures from conventional bridge design and construction—but aren’t so radical that further adoption would be impossible.
The results of the 11 bridge evaluations, each of which followed a protocol specific to the bridge, are contained in a mini-report as part of this final report. Each mini-report documents general bridge information, briefly describes the innovation used, and provides the result of the evaluation.
About the research
In bridge abutment design, the Wisconsin Department of Transportation (WisDOT) assumes the granular backfill material used behind bridge abutments as free-draining and no hydrostatic pressures are applied on the wall. This research investigated whether backfill materials meet the assumption of a freely-drained condition through a detailed laboratory and field study. In addition, the researchers investigated the viability of using recycled-asphalt pavement (RAP) and shingles (RAS) for granular backfill.
Laboratory testing involved characterizing the materials in terms of gradation/classification, erodibility, permeability, shear strength, and volume change (i.e., water-induced collapse). Laboratory tests revealed bulking moisture content for natural materials and collapse upon wetting. RAP and RAS materials exhibited collapse upon wetting and creep under constant loading.
The researchers performed scaled abutment model testing to assess pore pressure dissipation rates for the different materials and calibrate input parameters to predict drainage using fine element analysis (FEA). Abutment model testing indicated that addition of geocomposite vertical drain can substantially increase pore pressure dissipation rates and avoid material erosion.
Field testing involved in situ permeability, shear strength, and moisture content testing, and monitoring lateral earth pressures and pore pressures behind abutment walls at four bridges.
Results indicated that field conditions are more complex than the simple linear stress distribution typically assumed in the design for lateral earth pressures. Lateral earth pressures were greater than assumed in design over a majority of the monitoring period of this study.
Pore pressures behind an abutment wall were observed at one site following flooding. Predicted pore pressure dissipations using numerical analysis matched well with the measured values.
The researchers provided recommendations specific to the current WisDOT practice for abutment granular backfill design and construction as part of this project.