A Loading History Study of Two Highway Bridges in Virginia: Final Report

About the report:

An evaluation of the stress ranges in two typical highway bridge spans under service loadings was made in a cooperative study by the Virginia Highway Research Council and the Federal Highway Administration. The strains at selected points on the superstructure elements of the spans were recorded continuously for periods of four and five days under normal traffic conditions by means of an automatic, computer-controlled data acquisition system, and converted to stress on the basis of assumed moduli of elasticity. The weights, axle spacings, and lateral positions by lane of trucks crossing the instrumented spans during the test periods were also recorded, to the degree possible. The study proved the feasibility of utilizing the data acquisition system, which was developed for the FHWA, to obtain an indication of the service life to be expected of the test structures under today's truck traffic. The magnitudes of the stress ranges measured in the two simply supported test spans, a 76-foot steel beam composite span and a 60-foot prestressed concrete beam span, were considered acceptable, and it was concluded that both structures could safely accommodate an increase in traffic volume under current load limitations. The stress ranges recorded in the prestressed concrete beam span were low, indicating that fatigue considerations may not be critical in the case of such relatively massive spans of moderate length. However, since fatigue life is a function of the number of loadings, which will increase, as well as the magnitude of the stress ranges, the experimental results were not interpreted as justifying an increase in allowable weight limits, particularly in the case of the steel beam span. A theoretical correlation between the recorded truck characteristics and the measured bridge response is also presented. While refinement of the analytical methodology is necessary to improve the correlation, the analysis, which is based on accepted theory, did serve to verify the magnitude of the experimentally obtained stress ranges.

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