On 27 August, 2006, the Vincent Thomas Bridge, a critical 1850-m suspension bridge, located in the metropolitan Lost Angeles region had a collision with a large cargo ship, passing under the bridge. This incident left the transportation authorities wondering about the structural integrity of the bridge. Immediately after the accident, the bridge was closed to traffic until structural engineers from the California Department of Transportation (Caltrans) completed an analysis of the bridge.

Interest in the field of structural health monitoring (SHM) has been growing at a fast pace in the recent past due to the great developments in the fabrication of innovative sensors, the ease of deploying sensor networks, and the associated high growth in the computational power that is becoming readily available with personal computers. Furthermore, the development of sophisticated digital signal processing tools for the analysis of vibration signatures of dispersed civil infrastructure system has generated a lot of interest in the application of such analysis tools, in conjunction with real-time monitoring approaches, in order to perform virtually continuous condition assessment of any instrumented structure.

A real-time continuos monitoring system has been developed by the researchers at the University of Southern California, and deployed onto the Vincent Thomas Bridge since 2005. Using the monitoring system, the dynamic response of the bridge was successfully recorded before and after the incident as well as during the collision process. The analysis of these valuable data allows the transportation authorities to quantify the effects of the collision on the bridge structural condition, which would otherwise be infeasible with traditional visual bridge inspection approaches.

A forensic study was performed to assess the structural condition of the bridge before and after the incident. Relatively long time history records of the bridge oscillations were used to analyze its nearly stationary response by applying multi-sensor system identification approaches, utilizing the NExT-ERA methods. Both global and local identification methods were applied to detect significant changes in the bridge vibration signature. The identification results shown that there are no significant system changes due to the collision.

By utilizing web-based SHM system that is installed on the bridge, it is demonstrated that analysis of the acquired sensor measurements can provide the owners of critical infrastructure system with a forensic tool that enables reliable and rapid assessment to analyze the circumstances and consequences of extreme events to which the target system is subjected.

– Yun, H-B., Nayeri, R.D., Masri, S.F., Wahbeh, M., Tasbihgoo, F., Caffrey, J.P., and Sheng, L-H., “A Forensic Study of the Collision of a Cargo Ship with the Vincent Thomas Bridge,” Proc. of World Forum on Smart Materials and Smart Structures Technology 2007, 22-27, Chongqing and Nanjinng, China, 2007.