LOAD RATING OF SHORT-SPAN HIGHWAY BRIDGES

Results of field tests on five short-span bridges -- four reinforced concrete and one concrete-encased steel -- illustrate the difficulties in using service-load response for estimating load capacity of highway bridges. Tension steel strain and deflection induced in the five structures were measured, when subjected to moderate truck loads (about 90 percent of HS-20). Findings include: 1) induced strain and deflection are much lower than expected from analytical methods, 2) concrete deterioration does not cause a noticeable change in measured structural response, and 3) test data cannot be extrapolated to inventory and operating load levels with confidence. In a secondary series of tests, concrete strength estimates from ultrasonic pulse velocity measurements were found to be unreliable. (FHWA)