Evaluation of bridge rating methods

The 2001 Iowa National Bridge Inventory (NBI) Report (11) indicated that of the 25,138 bridges in Iowa, 7,102 (29%) are neither structurally deficient or functionally obsolete. While many of these bridges may be strengthened or rehabilitated, some simply need to be replaced. Another option, however, for managing these structures is to perform diagnostic load testing on bridges that are structurally deficient. Frequently, diagnostic load tests reveal strength and serviceability characteristics that exceed the predicted codified parameters. Usually, the codified parameters are conservative when predicting the load distribution characteristics and the influence of other structural attributes; hence the predicted rating factors are often conservative. In cases where calculations show a structural deficiency, it may be very beneficial to apply a tool that utilizes a more accurate model that incorporates field-test data; at a minimum, this approach would result in more accurate load ratings but will more frequently result in increased rating factors. Bridge Diagnostics, Inc. (BDI) developed hardware and software that is specially designed for performing bridge-ratings based on data from physical testing. The hardware consists of pre-wired strain gages, a data acquisition system, and other components. The software consists of three separate programs for visually evaluating test data, developing an analytical model, analyzing and calibrating the model, and performing load-rating calculations with the calibrated model