Peculiar dynamic response of a multi-span bridge with steel orthotropic deck

Selected results collected in the dynamic characterization of a multi-span bridge with steel orthotropic deck are reported in the paper. The bridge exhibits a span composition of (24.0 + 7x30.0 + 24.0) m, where the steel deck plate - 13.3 m wide - is stiffened in both the longitudinal and transverse directions and is supported by two main longitudinal girders; the distance between the main girders is about 7.50 m, with the girders’ height being of 1.40 m whereas the transverse cross-beams connecting the girders are only 0.675 m high. It is worth noting that the deck also exhibits a slight curve and a transverse slope of the cross-section of about 3.5°. Within the systematic monitoring activity recently promoted by the Italian Government, a dynamic monitoring system has been installed on the bridge; hence, to verify the accuracy and reliability of the monitoring devices, 3 spans of the bridge were instrumented using high quality accelerometers. The dynamic characteristics turn out to be very peculiar, with the vibration modes of the two main girders exhibiting different natural frequencies. To better explain the observed dynamic behavior, a detailed numerical finite element model of the viaduct was developed and validated against the experimental modal parameters. Furthermore, selected results from the bridge dynamic monitoring are reported as well.