Date of this Version
Development of a valid live load model is essential for assessment of serviceability and safety of highway bridges. The current HL-93 load model is based on the Ontario truck measurements performed in 1975. Since that time truck loads have changed significantly. Therefore, the goal of this study is to analyze 2005-2007 Weigh-In-Motion (WIM) data and develop a new statistical live load model.
The analyzed WIM data includes 47,000,000 records obtained from different states. A special program was developed to calculate the maximum live load effect. Comparison of the old and new truck data showed that on average Ontario trucks are heavier then the vehicles obtained from the available WIM and extrapolation of the data will yield the same maximum value. Exceptions are the extremely loaded sites from New York Sites and California.
Three types of live load models were developed; heavy, medium and light. Assuming 75 year return period the cumulative distribution functions of the load effects were extrapolated.
Development of the HL93 load was based on the analysis of several loading cases and it was found that two fully correlated trucks produce the maximum load effect. To verify simultaneous occurrence of two fully correlated trucks on the bridge a coefficient of correlation for available WIM data was determined and multiple presence analysis was performed. Analysis showed that this assumption is conservative. Based on the available data simultaneous occurrence of two fully correlated trucks is negligible.
Six steel girder bridges were selected and designed according to AASHTO LRFD code. FEM analysis of the selected bridges showed that the code girder distribution factors are conservative. Probabilistic analysis was performed and resulted with reliability indices higher than the target reliability 3.5. Based on this study it can be stated that HL93 load model is still valid for the highway bridges across US. An exception can be state of New York. Although the minimum calculated reliability index is equal to 3.8 a closer analysis of sites in New York is necessary.