The principal objective ofÂ Pooled Fund Project TPF-5(283): The Influence of Vehicular Live Loads on Bridge PerformanceÂ is to quantify the influence of vehicular live loads, particularly truck loads, on the long-term performance and durability of highway bridges. Bridge owners have much interest in this objective because of the diversity of truck loads and configurations currently operating on the Nationâ€™s highway bridges and because the freight industry has proposed increasing the allowable truck loads. Currently, the data available for evaluating the influence of truck loads on the performance and durability of highway bridges are incomplete and are largely qualitative or empirical in nature. This pooled fund study seeks to answer the principal objective through robust and systematic data collection to quantitatively characterize the current truck loads on the Nationâ€™s highway bridges, measure and quantify how various bridge elements respond to different truck loads and configurations, and track the long-term changes in the measured bridge responses to truck loads.
In addition to the principal objective described above, the pooled fund study includes a number of related objectives including the following:
- Develop a national bridge traffic database.
- Develop protocols for collecting high-quality bridge traffic data.
- Develop tools and products that bridge owners can use to better quantify and manage loading conditions on the existing network of highway bridges.
The pooled fund study includes a number of tasks that were devised to meet the project objectives. The following is a summary of these tasks:
- Conduct a literature review of available weigh-in-motion (WIM) data collection technologies and systems. This task has been completed. The report, FHWA-HRT-16-024, â€śLTBP Programâ€™s Literature Review on Weigh-In-Motion Systems ,â€ť was published in June 2016.
- Review the Long-Term Pavement Performance (LTPP) Programâ€™s experiences with WIM systems and traffic data collection obtained through the execution of pooled fund study TPF-5(004): Long-Term SPS Traffic Data Collection.
- Identify and evaluate alternative approaches for collecting the necessary data to meet the project objectives.
- Identify optimal bridge sites for data collection and the number of test sites to be included in the study.
- Develop a data collection program for the study that includes recommended methods and protocols for measuring and analyzing bridge traffic and bridge responses at the test sites.
- Implement the data collection program, maintain the measurement systems, and collect and analyze the data at selected bridge sites for a period of two years.
- Archive the data collected in this study in a format suitable for inclusion in the Long-Term Bridge Performance (LTBP) Bridge Portal.
The bridges selected as data collection sites for this study will also be classified as reference bridges in the LTBP Program. Reference bridges in the LTBP Program are subject to a spectrum of detailed data collection efforts and protocols that are in addition to the data collection efforts specific to the pooled fund study.
Periodic reviews of the progress and deliverables for each task have been provided by the Federal Highway Administration (FHWA) LTBP Program team, a Technical Advisory Committee consisting of representatives from the State transportation departments participating in the pooled fund study, and the Transportation Research Board (TRB) LTBP Expert Task Group on Traffic and Truck Weights.
As of January 2018, the first five project tasks have been completed, and the data collection program is being implemented for several test bridge sites. The selected test bridge sites are located in States participating in the pooled fund study. Currently, a prestressed concrete multi-beam bridge in Oregon, a continuous steel multi-beam bridge in Wisconsin, and a continuous steel multi-beam bridge in Georgia have been included as test sites for the study.
The Oregon bridge was constructed in 1969 and carries two lanes of Iâ€“84 West over County Road 1133 in Umatilla County. The bridge consists of three simple spans and has an overall length of 160 feet. The superstructure consists of a cast-in-place (CIP) composite reinforced concrete deck on AASHTO Type III prestressed beams. The Wisconsin bridge was constructed in 1961 and carries the two westbound lanes of U.S. Highway 2 over the Montreal River in Iron County. The bridge has three continuous spans with an overall length of 120 feet, and its superstructure consists of a CIP, composite reinforced concrete deck on W24x76 rolled beams with cover plates. The Georgia bridge was constructed in 1977 and carries two southbound lanes of I-85 over S.R. 109 in Troup County. The Georgia bridge is configured with two simple end spans and a two span-continuous middle section. The continuous span section is being monitored for this study and has a span length of just under 167 feet. The superstructure of the Georgia bridge consists of W36 rolled beams with cover plates and a CIP composite reinforced concrete deck.
The test bridges are instrumented with strain gages, temperature sensors, accelerometers, displacement gages, tiltmeters, weather stations and overview cameras. Each bridge test site also has a Weigh-in-Motion (WIM) system located near the bridge that records the weight and geometric characteristics of the trucks crossing the bridge. The bridge monitoring system operates in a high-speed triggered mode that records the bridge response at 200 Hz for 6 seconds and records a snapshot image of the traffic on the bridge each time a truck crosses the structure. Thermal inputs and the related bridge responses are also measured once every 15 minutes on a continuous basis.
The measurement data being collected at each bridge characterizes the full spectrum of structural loads and the corresponding load effects. These measurements are being analyzed and evaluated to quantitatively document the effects of truck loads on highway bridge performance and durability. Pennoni will be developing tools to help bridge owners better manage the truck loads on their bridges using the results from this study.
The current participants in the pooled fund study include the FHWA LTBP Program and the transportation departments from the following seven States: Georgia, Iowa, Minnesota, North Carolina, Oregon, Pennsylvania, and Wisconsin. The study is being executed by engineers from Pennoni’s Intelligent Infrastructure Systems division.