Physics-based traffic excitation models for highway bridges

Abstract

For long-term bridge health monitoring, structural dynamic properties are usually obtained by system identification based only on the system output (bridge vibration responses), because the system input (traffic excitation) is difficult to measure. To facilitate such identification the excitation is commonly assumed as spatially uncorrelated white noise. However, when physically modeling it as a stationary stream of moving forces traversing the bridge, whose arrivals at the bridge are in accordance with a Poisson process, the traffic excitation is found to be spatially correlated. In this paper a procedure for formulating the traffic excitation model based on its physics is proposed, which involves first converting the moving forces into equivalent nodal excitation time-histories by the dynamic nodal loading approach, and then applying the Campbell's theorem for the filtered Poisson processes. By this procedure, a non-diagonal frequency-variant excitation spectrum density matrix (SDM) is obtained. This does not conform to the conventional white noise excitation model. One of the output-only identification techniques based on the conventional excitation model, the frequency domain decomposition technique is implemented to demonstrate that direct application of the technique to traffic-induced vibrations can lead to misleading results. The proposed procedure for formulating the traffic excitation SDM provides a way to describe primary knowledge of the traffic excitation in frequency domain even for complicated bridges, which will potentially enable improvement in output-only identification techniques with unknown but spatially correlated excitation.

Sensor Network for Structural Health Monitoring of a Highway Bridge

“…Workshop on Structural Health Monitoring 2005 Recently, efforts have been underway to include traffic load as the source of dynamic excitation with the aid of video imaging ͑Elgamal et al. 2003, 2004Chen et al 2004Catbas et al 2004; . Generally, image tracking for traffic applications is an area of increasing interest with a large scope of potential applications ͑e.g., Beymer et al 1997;Collins et al 2001;Kogut and Trivedi 2001;Morris and Trivedi 2006͒.…”