USDA Forest Products Laboratory
Brent Pharesbphares@iastate.edu email >
Bridge Research Engineer, BEC
About the research
Most engineering analyses of historic covered timber bridge trusses are based solely on routine site inspections. In addition, assumptions about the behavior of connections and support conditions are made during the systemic analysis stage. This approach can lead to inaccurate and, in most cases, overly conservative load-capacity ratings for these historic structures.
By conducting live-load testing to assess the overall performance of the superstructure system, engineers will be able to perform structural analyses in a more reliable fashion. The measured live load response should also provide a measure of the effectiveness of various structure modeling techniques. The end result should be a more reliable approach to assigning safe load-capacity ratings for historic covered bridges.
During Phase I of this project, 11 covered bridges were evaluated by live-load testing methods: three covered bridges in Parke County, Indiana, built of variations of the Burr-Arch truss configuration; four other covered bridges in Indiana built of variations of the Howe truss configuration; and four covered bridges in Vermont built of variations of the Queen post truss configuration.
This study will continue the work initiated in Phase I to develop and establish recommended procedures for safely and reliably load-rating historic covered bridges through physical testing.
- Develop field protocols for live-load testing of historic covered bridges, in conjunction with analytical modeling data requirements
- Conduct live-load testing on several bridges representing the main truss types that have been preserved
- Analyze load-testing field data and disseminate data to analytical modeling efforts
- Develop a rationale for incorporating physical test data into existing load-rating procedures
- Prepare a comprehensive guidance manual that documents recommended procedures for live-load testing and enhanced load rating of historic covered bridges