This paper presents and discusses issues related to structural identification, calibrated model-based load rating, and sensitivity of rating to the analytical model, along with experimental studies conducted on an existing concrete-deck-on-steel-stringer bridge. The proposed model-updating procedure uses collected dynamic data (mode shapes, modal frequencies, and order of modes) as well as static deformed shape information. Two-dimensional (2D) grid models were developed to successfully simulate the transverse load transfer mechanisms between girders, torsional flexibility, and effects of skewed bridge architecture. The rating results obtained from the 2D-grid models were close to 3D-FEM-based evaluation, while simplified 1D bar models had serious shortcomings. Grouping the parameters of the analytical model at different stages of model calibration enhanced the speed and convergence success of the objective function. Although cross-braces are considered as non-structural members, they have been found to be the most critical members of the selected bridge during rating studies. Failure of cross-braces deemed to alter the load transfer mechanism between girders and possibly resulting in the premature failures of interior girders. (C) 2011 Elsevier Ltd. All rights reserved.