Impact of Superimposed and Truck Live Load on Modal Characteristics of Short-Span Bridges

Modal analysis characterizes the dynamic behaviour of structures, by means of their natural frequencies and mode shapes. Since these parameters are related to the flexural stiffness, many damage detection methods are based on measuring the vibration response of a structure. In particular, operational/ambient modal identification deals with cases where vibration is measured under operating conditions. In these circumstances, the exact nature and magnitude of the excitation forces is unknown and the frequencies measured on the structure may differ from those extracted in free vibration. In this paper, the vibrational response of a single short-span bridge deck, consisting on a simply supported slab, is simulated for different distributions of mass throughout the structure and the action of two typical 5-axle European trucks to address how modes and frequencies are affected by superimposed dead and live traffic loads. While the analysis focuses in the change of bridge frequencies, vehicle frequencies are also briefly discussed.