| There is a growing need to develop efficient methods for evaluation of existing bridges. Underestimation of the bridge load carrying capacity can have serious economic consequences, as deficient structures must be repaired or rehabilitated. Therefore, knowledge of the actual bridge behavior can lead to a more realistic evaluation and elongation of the remaining service life with or without repairs.; The objective of this study is to develop a methodology for evaluation of the load carrying capacity for existing bridges, to accurately determine the safety margin, and to investigate the validity of the current code evaluation methods based on the experimental and analytical results.; Seventeen existing bridges were tested using truck loads to confirm their adequacy for carrying traffic loads. The actual responses were measured. The code specified factors, in particular, the girder distribution factors (GDF) and dynamic load factors (DLF), are reviewed and compared with the test results. A finite element analysis is performed for selected bridges. The models are calibrated using field measurement data. The finite element analysis shows that the partial support fixity and unintentional composite action are the main reasons for the low strain values.; The statistical models of GDF and DLF are developed based on the test and FEM results. Such models involve less uncertainties compared to those based solely on analytical model. A new formula is proposed for GDF. The proposed GDF's are closer to the actual values compared to those specified in the AASHTO Standard (1996) and AASHTO LRFD (1998).; A reliability analysis procedure is developed and applied to the selected bridges. Deterministic rating factors are also calculated. It is shown that the rating factors and the reliability indices of selected bridges can be significantly improved by including the results of field measurement into calculation. The bridge evaluation based on the deterministic rating can be often too conservative for bridges carrying low volume traffic. |
