Quantifying Field-Test Behavior for Rating Steel Girder Bridges

Field testing is valuable for evaluating existing bridges. It allows the owner to reduce the conservatism of analytical rating methods and safely rate the bridge for higher loads. Many factors not considered in design contribute to the response of a tested bridge. Several of these, like actual load distribution and additional stiffness from curbs and railings, are welcome benefits that can be used to increase load ratings. However, there are also contributions from bearing restraint forces and unintended composite action that may not be reliable during the bridge's service life. These factors tending to increase the load capacity need to be separated and quantified so that the bridge owner can: (1) confirm the origin of the useable benefit; and (2) remove the unwanted contributions. Presented are procedures for load rating steel girder bridges through field testing. A systematic approach is presented to separate and quantify the contributions from various effects. Therefore, the responsible engineer can remove the unwanted contributions and justify an experimental load rating. The procedures are demonstrated for a three-span steel girder bridge.