Instrumentation of bridges for long-term performance monitoring

As the state of the art in bridge design is advancing toward the performance-based design, it becomes increasingly important to monitor and evaluate the long-term structural performance of bridges, including strains in critical structural members, soil pressures on the abutment back walls and footings, accelerations on the decks and bents, etc. Such information is essential in developing new performance criteria for design. In this research, sensor systems for long-term structural performance monitoring have been installed on two new highway bridges in Orange County, California: the Jamboree Road Overcrossing and the West Street On-Ramp. They include accelerometers, strain gauges, pressure sensors, displacement sensors, installed or embedded at strategic locations of both super- and sub-structures. Data recorders and power supplies have also been installed at the bridge sites. Preliminary vibration measurement and data analysis have been performed on these instrumented bridges. On the Jamboree Road Overcrossing, ambient vibration data have been collected, based on which natural frequencies and mode shapes have been extracted using various methods and compared with those obtained by the preliminary finite element analysis. On the West Street On-Ramp, braking and bumping vibration tests have been carried out using a water truck in addition to ambient vibration tests. Natural frequencies and mode shapes have been derived and the results by the breaking and bumping vibration tests have been compared.