Pooled Fund Project TPF-5(283): The Influence of Vehicular Live Loads on Bridge Performance
The principal objective of this pooled fund study 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 Nation'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 Nation'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. Report FHWA-HRT-16-024, LTBP Program’s Literature Review on Weigh-In-Motion Systems, was published in June 2016.
- Review the Long-Term Pavement Performance (LTPP) Program’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 2 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 July 2016, the first five project tasks have been completed, and the data collection program is being implemented. A prestressed concrete multibeam bridge in Oregon and a steel multibeam bridge in Wisconsin have been identified as initial test sites for the data collection program. The sites were chosen from bridges located in States participating in the pooled fund study using selection criteria consistent with that used by the LTBP Program to select reference bridges. Several additional criteria were also considered, including proximity to existing weigh stations or WIM sites, average daily truck traffic (ADTT) characteristics, ease of access, and proximity to electrical power service.
The prestressed concrete bridge carries two lanes of I–84 West over County Road 1133 in Umatilla County, OR. The bridge, constructed in 1969, is located approximately 30 miles west of the Emigrant Hill Weight Enforcement Station. The bridge consists of three simple spans (deck continuous for live load) and has an overall length of 160 feet. The superstructure consists of a cast-in-place (CIP) reinforced concrete deck on American Association of State Highway and Transportation Officials Type III prestressed beams. The 2013 average daily traffic (ADT) for the bridge was 7,400, with 29 percent trucks.
The data collection program for the prestressed concrete bridge site includes the installation of a new WIM site in the pavement just east of the bridge and instrumentation of bridge components located in the middle span of the structure. The new WIM site includes an overview camera and will classify and measure the weights of vehicles in the two traffic lanes that cross the bridge. Various sensors installed on the bridge elements will measure and record how the bridge responds as the vehicles characterized by the WIM site cross the structure. Data collection from this test site is expected to begin in October 2016.
Figure 1. Photo. Prestressed concrete multi-beam bridge site-aerial view.
Figure 2. Photo. Prestressed concrete multi-beam bridge site-side view.
Figure 3. Photo. Steel multi-beam bridge site-aerial view.
The data collection program for this bridge will take advantage of the existing LTPP WIM site to collect classification and weight data for the vehicles crossing the structure. Various sensors will be installed on the bridge elements to measure how the bridge responds when the vehicles characterized by the WIM site cross the structure. Data collection from this site is expected to begin in the spring of 2017.
The results obtained and lessons learned from the data collection programs at these two bridge sites are expected to be used to further refine the design and execution of the data collection program for future bridge sites included in the 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 Associates Inc.