About the research
To account for the dynamic loads imposed by passing vehicles, the Standard Specifications for Highway Bridges of the American Association of State Highway and Transportation Officials (AASHTO) prescribes that dynamic allowance be applied. Historically AASHTO has not contained a provision for dynamic allowance for wood bridges. Recently, the exclusion of wood bridges from dynamic allowance requirements has been questioned. This issue was doubly important given the recent major revisions to the specification. Recent studies have shown that the dynamic allowance can account for a significant portion of the total response and thus should be considered. The objective of the research was to determine the dynamic performance characteristics of timber bridges, including stress-laminated deck, longitudinal deck and glued laminated stringer bridges. A matrix of field bridges of each type was identified and field load tests were performed. Both bridge deflection and acceleration data were collected during the load testing. In addition, test truck acceleration data were also collected. An analytical study was performed to further study the bridges? dynamic performance and design recommendations were developed for inclusion into the AASHTO Standard Specification for Highway Bridges.