National Center for Wood Transportation Structures

About the research

State and federal legislators regularly request increases to the axle or gross weight limits for commercial vehicles. The question that is always asked is, “What is the impact on the life expectancy of a bridge when heavier loads are allowed on some vehicles?” There is no past or present method to determine how heavier loads affect the life of Iowa highway bridges. Bridge owners need a method of quantifying the effects of heavier loads or any load on a bridge’s life expectancy. The objective of this research is to qualify the relationship between increased legal loads and reduced bridge service life for Iowa bridges. To achieve the proposed objective, a 36-month research plan was developed, which includes conducting a comprehensive literature review, collecting Iowa-specific data, estimating bridge costs and life reduction due to truck weight limitation increases, and performing the laboratory test for the validation of bridge life reduction prediction. The result of this project will help the bridge owner make reasonable assumptions on the life of a bridge when subjected to increased truck loads.