Intelligent Infrastructure Systems was engaged to perform a full-scale ambient vibration test of the suspension bridge superstructure and towers to support a seismic vulnerability investigation for the structure. The field testing program was developed based on our experiences with vibration testing of other major long-span bridges and employed a stationary accelerometer array that was distributed between the towers, the main span, and the side spans with a mobile accelerometer array that was roved across the entire structure. The field measurement program produced redundant records of the global ambient vibration response of the structure with high spatial and temporal resolution.
A systematic data quality assurance and analysis procedure was employed to identify the natural frequencies, mode shapes, and damping ratios for the structure. These identified dynamic characteristics were used in conjunction with 3D finite element (FE) models of the bridge to assess its seismic vulnerability.
The owner was able to recognize a savings of approximately $10 million resulting from the development of a cost-effective seismic retrofit design based upon the enhanced, specific findings that were made possible by combining the field measurement results with the finite element analysis efforts.