Methods for reducing the output scatter of results for determining realistic damping factors of railway bridges

Abstract

A realistic and economical computational assessment of the dynamic behaviour of railway bridges requires input parameters that correspond to reality. In this context, the computationally applied damping factor has a decisive influence on the results. However, the standard prescribes damping factors regarded as highly conservative, which makes in-situ measurements on structures often necessary to classify a bridge categorized as critical in prior as non-critical. Regarding in-situ tests, a measurement-based determination of the damping factor is inevitably accompanied by a scattering of the results due to the measurement method used and results from the individual scope of action of the person evaluating the test. This contribution presents methods and analysis tools for determining the damping factor in the frequency and time domain, intending to reduce the scatter of results and limit the scope of action of the evaluating person. Based on a single-degree-of-freedom system, more advanced procedures and methods are presented and explained using an exemplary steel railway bridge. The basic idea is to use the least square method to adjust the recorded amplitude-frequency response (frequency domain) or the decay process (time domain) based on in-situ measurements by a mathematically defined curve.