Dynamic monitoring of an isolated steel arch bridge during static load test

This paper describes the dynamic monitoring carried out by means of vibration measurements during the standard static load test of a half-through steel arch bridge on the Potenza river. The structural design of the bridge is characterized by some notable aspects: the river crossing is obtained by two coupled steel arches, having a span length around 115 m, and a steel-concrete composite deck sustained by thirty couples of steel hangers; the approaching spans are realized with continuous girders on intermediate supports, having cross section with variable height; the arches are supported on rubber bearing seismic isolators. The vibration measurements were nearly continuously acquired during the loading tests to detect the occurrence of anomalies in the structural behavior. In particular, the global dynamic characteristics of the structure, in terms of modal parameters, were determined using the data set of measurements at specific phases of the load test: first on the unloaded configuration, then on two different loaded configurations and finally after the bridge unloading. Measurements of vibrations due both to the ambient and to the impulse produced by a fully loaded truck passing over a bump, were carried out. The experimental results, in terms of modal parameters of the bridge, are in agreement with the theoretical results obtained with the predictive finite element model developed for design purposes and opportunely modified to account for the real conditions of the bridge during the tests.