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The International Guadiana Bridge is a cable-stayed bridge crossing the Guadiana River, which marks the southern border between Portugal and Spain. The bridge has a central span of 324 m and a total length of 666 m and was open to traffic in 1991. Despite the globally satisfying behaviour under the common environmental loads, which largely ensures the bridge serviceability, frequent episodes of cable vibration have been observed since completion of the construction. In this paper, the bridge modal properties and dynamic behaviour, identified from repeated campaigns of vibration data acquisitions, are compared with the response of a three-dimensional finite element model, including the description of the cable transversal motion. The model, after minor updating, furnishes a realistic reproduction of the current bridge dynamic behaviour. Then different possible justifications of the local vibrations are evaluated, briefly scanning the known sources of large amplitude cable oscillations both in the linear and the nonlinear field. In particular, the occurrence of different internal resonance conditions is deeply discussed, in order to verify whether the experimental observations could be really justified by a cable-deck dynamic interaction mechanism. Among different possibilities, a beating phenomenon between two resonant modes, amplified by the lower damping and inertial characteristics of the local mode with respect to the global one, is selected as the most critical cable excitation source. Since the cable vibrations are proved to persist for different wind conditions, the heavy traffic load on the bridge deck is investigated as one possible source of the global mode direct excitation. On this respect, the model response to random load and moving forces acting on the bridge deck is numerically evaluated evidencing how some particular features of the real bridge behaviour can be qualitatively reproduced.

SUMMARY The entire structural identification process, starting from measurement of the experimental response to ambient vibration, and concluding with the assessment of a representative dynamic model, depends upon an informed selection of appropriate data treatment techniques. The paper compares different procedures for identifying both modal and physical models. Four approaches (EFFD, ERA, SSI, and TFIE) for output‐only modal identification are discussed. Their performance is evaluated using experimental data extracted from the ambient vibration response of a three‐dimensional frame. The discussion of the identification results throws light on the intrinsic characteristics of each procedure, while the particular features of the structure, presenting unexpected local modes, demonstrate the necessity of a hierarchical treatment of the available information, based on a solid engineering knowledge. The calibration of a physical model is approached using an exact inverse procedure, based on a parametric analytical model, or automatic techniques of error minimization, based on finite element multi‐models. The achievement of a good relative agreement, measured through performance‐based indexes, increases the general confidence on the results independently obtained from each modal identification and model updating method. Copyright © 2011 John Wiley & Sons, Ltd.

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The development of a reliable bridge management system (BMS) constitutes a formidable engineering challenge due to both the multiobjective nature of the task and the large amount of information to be considered in formulating the required automated judgments. This article deals with a procedure for bridge condition assessment by visual inspection developed during the planning and preliminary design of the BMS for the public railway networks in Italy. The main modules adopted in the procedure are: bridge inventory, computer‐aided visual inspection, automated defect catalog, and priority‐ranking procedure. The probabilistic models used to calibrate the condition evaluation algorithm are discussed. Different levels of deficiency have been individuated for each class of bridge structure belonging to the managed stock. The procedure allows comparison and relative ranking of deficiency conditions across different types of bridge structures. The results of a visual inspection campaign conducted for a set of bridges with different structural characteristics are reported and evaluated within the framework of the developed BMS.