Subjective and Objective Evaluations of Bridge Damage

A decommissioned, 40+-year-old reinforced concrete deck on a steel girder bridge was subjected to a series of induced damages, nondestructive field tests, and visual evaluations to compare objective and subjective methods of bridge-condition assessment. Prior subjective evaluations of bridge condition often produced highly variable results. For example, inspectors with different backgrounds and field experience disagreed on how severely certain forms of deterioration and damage influenced bridge behavior and safety so, consequently, different assessments of bridge condition were generated. Furthermore, a load rating of the “as-is” state of the bridge (e.g., the state before any induced damages), according to current Ohio Department of Transportation procedures, indicated that the bridge could only support truckloads of 227 804 N (51,192 lbf). However, the objective data acquired during nondestructive field testing of the bridge, which was subjected to truckloads of 282 130 N (63,400 lbf), revealed maximum superstructure deflections and live-load stresses of 0.190 cm (0.075 in.) and 15 985 kPa (2,320 psi)—values well within AASHTO limits. These values also imply that the bridge can support loads much greater than those indicated in the load rating. Comparing subjective and objective assessments for the induced damage scenarios yielded similar results. Essentially, data revealed that subjective methods of bridge evaluation and assessment were unable to properly characterize intrinsic bridge mechanisms and the influence that such mechanisms have on bridge behavior. Condition assessment of a typical reinforced concrete deck on a steel girder bridge should therefore include objective evaluations of bridge condition and behavior.