Abstract Summary
The author has proposed a vehicle-based (coupling of a moving vehicle and a bridge) bridge health monitoring system by using public buses which is one practical solution to the problem for condition assessment of short and medium span(10-30m) bridges. The vehicle-based measurements with public buses as part of a public transit system are used to detect anomalies (deterioration) of the target bridge by analyzing long term vibration measurement data collected while the vehicle (bus) crossed the target bridges, mainly vertical acceleration da-ta, as obtained from the acceleration sensor installed under the rear wheel spring of an in-service fixed-route bus. Main reasons for using an in-service fixed-route bus (i.e. a heavy vehicle) are as follows: ① If a vehicle of about 10 m length is used for measurement, it is highly likely that the vehicle is alone on the lane when it crosses a short or medium span bridge, ② A relatively heavy vehicle is needed to produce significant vibration of short and medium span bridges which have relatively high flexural stiffness, ③ A fixed-route bus used as a source of bridge excitation, easily allows to reproduce measuring conditions such as the time of passage, route, frequency and velocity, ④ Since a fixed-route bus equipped with a sensor makes the rounds, it is possible to monitor mainly short and medium span bridges in a partic-ular area on a regular basis. As a result, substantial cost savings can be achieved because there is no need to install sensors to all bridges to be monitored, and ⑤ The electric power for the measuring instruments used can be supplied by the power supply of the bus. In this study, in order to evaluate the sensitivity of “characteristic deflection” which is a bridge health condition indicator used by the system, it has been field-tested over 10 years period by using an in-service fixed-route bus operating on a bus route in Ube city, Yamaguchi Prefecture, Japan. This paper describes not only the validation results obtained from the long-term monitoring and discusses the usefulness of the system but also the problems of the conventional observation method based on “characteristic deflection”, which is a bridge condition indicator that makes possible efficient detection of structural anomalies of the bridge being monitored, are identified, and a new observation method that enhances the damage detection sensitivity of the system is evaluated. As the results, it will be able to make a rational long-term health monitoring system for existing short and medium span bridges, and then the system helps bridge administrators to establish the rational maintenance strategies.
