Data-base with in-situ vibration frequencies of bridges in Portugal

Abstract

A data-base of 285 bridges in Portugal was composed with information about the geometric characteristics like largest span length, height and cross-section, as well as the main vibration frequencies with special emphasis on the frequency of first vertical mode. This data-base includes different bridge typologies ranging from reinforced concrete (RC) box girders and RC beam bridges, steel girder bridges, steel truss bridges, RC arch and stone bridges, cable-stayed bridges and suspension bridges. Each one of the bridges was subjected to an in situ test with a single 3-component accelerometric station and its main natural frequencies were determined. Very good correlation of the vertical frequency with largest span length was obtained for the first four typologies above referred. Good correlations were obtained for the transversal frequency with the total length of long span cantilever RC bridges. Numerical modelling was performed for six long span cantilever RC bridges and comparison with in situ frequencies in the vertical and transversal directions was made. Further discussion was made on the value of frequency estimation, in view of the uncertainties in methods and analysis, the changes that are observed along the lifetime and the corresponding interpretations. This last point is related to the continuous vibration monitoring of structures which is very important in damage detection.