Evaluation of Existing Bridges by Field Testing

The objective of the presented research is to develop an efficient control system for highway load effects that involves the control of various parameters including: truck weight (axle weights and axle spacing), truck load distribution on bridge girders, dynamic load, strain, stress and deflection of bridge components, and verification procedure for the minimum load carrying capacity. This study involves experimental and analytical efforts. The individual components of the comprehensive testing program were verified on over 20 bridges. The load was applied in form of fully loaded (up to the legal limit) trucks and military tanks. The considered loading combinations include a single vehicle and two trucks side-by-side. The results of these and previous tests indicate that the girder distribution factors (GDF) specified by the code (AASHTO) for the spans from 10 to 30m are rather conservative. Dynamic load factors (DLF) were also measured for a single truck and two trucks side-by-side. It was observed that the dynamic load is not related to static load, and therefore DLF (defined as the ratio of dynamic load and static load) decreases for larger static load. Deflections due to truck loads are also considerably lower than analytically predicted values. The field tests confirmed that the developed procedures are efficient and can be used as an alternative way to evaluate the adequacy of the bridge. Proof load tests using military tanks turned out to be efficient procedure for verification of the minimum load carrying capacity of a bridge.