Iowa Statewide Urban Design and Specifications

About the research

The Wisconsin Department of Transportation recognizes the importance of accurately assessing the timber deck slab bridge inventory within the state. Of the 571 timber bridges in Wisconsin, 450 bridges are timber slab bridges. Current methods of load rating employ equations first developed in the later 1980s and early 1990s for determining the equivalent strip width. These equations often produce results that unnecessarily penalize the bridge by requiring a posted weight limit.

Through a program of bridge live load tests and analytical modeling, the researchers in this study have both measured and modeled the bridge behavior with more accuracy and have shown the current equivalent strip width calculation methodologies to be conservative, as was originally speculated. Ten unique bridges were tested a part of this study. Three of them were tested twice; once before and once after bridge strengthening measures were employed. An equation to calculate the equivalent strip width was developed with numerous variables in mind.