PSI - Issue 64

Ayaho Miyamoto et al. / Procedia Structural Integrity 64 (2024) 464–475 Author name / Structural Integrity Procedia 00 (2019) 000–000

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sensitivity of “characteristic deflection” which is a bridge health condition indicator used by the system, it needs to apply the system to a practical bus network for a long-term period. The aim of this paper is to introduce the details of not only how to assess the bridge condition based on the results of long-term application (total more than 10 years) to actual bridges on Ube City bus network in Japan, as a specific example for verify the system but also what is possible steps in realizing practical application of the system to existing bridges for consideration systematically into the maintenance strategies in the future. 2. Outline of the bus-based monitoring system The bus-based monitoring system is the method of monitoring short and medium span bridges by using fixed-route buses operated as part of public transport systems. The aim of the system is to detect the transition from the “acceleration period(stage),” in which the safety performance of a bridge sharply declines because of aging, to the “deterioration period(stage)” (Miyamoto et al. (2019)) . Fig. 1 illustrates the bus-based monitoring system principle with the analysis flow of the monitoring method. Main reasons for using an in-service fixed-route bus (i.e. a heavy vehicle) are as follows: ① If a vehicle of about 10m length is used for measurement, it is highly likely that when the vehicle crosses a short and medium span bridge, that is the only vehicle in the same lane on the bridge, ② If a short and medium span bridge which has relatively high flexural stiffness is to be vibrated significantly, it is necessary to use a relatively heavy vehicle, ③ If a fixed-route bus is used as a source of bridge excitation, it is easy 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 particular area on a regular basis. As a result, substantial cost reduction 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. Regarding the above first item, vehicles moving in the opposite direction or oncoming vehicles are regarded as an external disturbance factor included in operational conditions in this study. The bus-based monitoring system by using local fixed-route buses is a rational system capable of monitoring bridges daily while serving as part of transport infrastructure. The system, however does not identify local deteriorations and their causes because the purpose of the system is to detect damage (anomalies) indicating an overall structural problem of a bridge. As shown in Fig. 1, the vertical displacement of the bridge and the bus under its rear wheel springs is an estimated deflection obtainable by integrating the vertical acceleration waveform twice. The displacement can be expressed, as the sum of (i) the static displacement dependent on bridge stiffness and bus weight, (ii) a non-steady-state vibration component having a stochastic nature characterized as a Gaussian process attributable to a rough road sur-face and having a mean value of 0, (iii) vibration components governed by the equation of motion such as the bridge and the vehicle, and (iv) external disturbance factors due to differences in the operating conditions of the bus and differences in data extraction and processing methods. For the purpose of this study, the “characteristic deflection” which is relatively free from the influence of dynamic disturbances due to the roughness of road surface, etc., is defined as an indicator that may be useful in efficiently detecting a structural anomaly of existing bridges(see upper right of Fig. 1). 3. Long term application of the system to actual bridges In here, it is described in detail on a long-term field test of the bus-based monitoring system for short and medium span bridges located on the municipal bus routes in the Ube city, Yamaguchi Prefecture, Japan conducted over a period of more than 10 years from Dec. 2010 to now, 2022. Since the field test has been conducted for more than 10 years, the data thus accumulated were utilized to evaluate the influence of fixed-bus operating conditions (external disturbance factors such as weather, the number of oncoming vehicles, the number of persons in the vehicle and vehicle speed) on “characteristic deflection” (Miyamoto and Yabe (2012), Yabe et al. (2015)) . 3.1. Target bridges on Ube-city's bus routes In order to develop and apply to practical use the bus-based monitoring system for short and medium span bridges located on bus routes, it is necessary to conduct a series of studies involving a long-term field test using an in-service fixed-route bus. In this study, with the cooperation of Ube-city Transportation Bureau (UTB), long-term monitoring