Most studies to date on live-load distribution factor (DF) determination have focused on the examinationof bridges under normal highway-type vehicles. Many bridges are in use on rural roadways whereagricultural vehicle travel is common and therefore the impacts of their atypical load types should beexplicitly considered. Developing systematic methodologies accounting for their effects are also criticalfor more reasonable safety assessment of rural bridges. The primary objective of this study is to develop astatistical framework to determine DFs for rural bridges subjected to agricultural vehicles. A samplebridge in a rural area of Iowa was selected for demonstration of the proposed statistical framework. Theproposed procedure consists of multiple parts including live load field testing, finite element simulations,and statistical analyses. A network of multiple strain sensors were installed at the critical locations on thebridge to monitor strain time histories resulting from passes of farm vehicles with known characteristics.Strains were utilized to compute field measured DFs and also used to calibrate analytical models. As partof the model simulation, farm vehicles commonly found in the United States were chosen and applied tothe model to calculate their DFs. Statistical thresholds for the exterior and interior girders were calculatedby performing a statistical analysis of the computed data. The thresholds were compared to the AASHTOcode-specified DFs (for both the Standard Specification and the LRFD Specification), indicating theinterior girder limit was below yet the exterior limit was above the AASHTO values.
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