Characterization of Reinforced Concrete Bridges Using Dynamic Response Measurements for Use in Load Capacity Estimation

摘要

The U.S. Army Engineer Research and Development Center (ERDC) is leading research efforts for the development of rapid bridge load-capacity assessment tools for the military, otherwise known as Military Load Classification (MLC). These tools may be used in the evaluation of the effects of heavy military-vehicles on civilian bridges and are based, in part, on field tests of concrete bridges. This field testing procedure is aimed at determining the MLC of a bridge by first estimating girder stiffness and considering load distribution effects associated with a test vehicle. This approach, while capable of providing the desired MLC estimate, does not provide an adequate measure of uncertainty or confidence in the estimate, since the field measurement may mask actual damage states in the bridge. Assessing the current condition of a bridge is a key component in the determination of its load- carrying capacity. As a result, tests in which the true condition of the bridge is determined can be useful in assessing the relative uncertainty or even the appropriate confidence level of the MLC estimate. This study describes field testing procedures using ambient, impact, and wave speed techniques on reinforced concrete bridges owned by the Virginia Department of Transportation. The ambient response measurements were used to determine fundamental characteristics including resonant frequencies and mode shapes, while the transient tests were designed to provide some measure of the relative condition that may exist between girders in the bridge. These measurements will supplement other measurements acquired using test vehicles and surveying techniques.