Largest portion of the bridge stock in almost any country and bridge owning organisation consists on ordinary bridges that has short or medium spans and are now deteriorating due to aging, etc. Therefore, it is becomi...Largest portion of the bridge stock in almost any country and bridge owning organisation consists on ordinary bridges that has short or medium spans and are now deteriorating due to aging, etc. Therefore, it is becoming an important social concern to develop and put to practical use simple and efficient health monitoring systems for existing short and medium span (10 - 30 m) bridges. In this paper, one practical solution to the problem for condition assessment of short and medium span bridges was discussed. A vehicle-based measurement with a public bus as part of a public transit system (called “Bus monitoring system”) has been developed to be capable of detecting damage that may affect the structural safety of a bridge from long term vibration measurement data collected while the vehicle (bus) crossed the target bridges. This paper systematically describes how the system has been developed. The bus monitoring system aims to detect the transition from the damage acceleration period, in which the structural safety of an aged bridge declines sharply, to the deterioration period by continually monitoring the bridge of interest. To evaluate the practicality of the newly developed bus monitoring system, it has been field-tested over a period of about four years by using an in-service fixed-route bus operating on a bus route in the city of Ube, Yamaguchi Prefecture, Japan. The verification results thus obtained are also described in this paper. This study also evaluates the sensitivity of “characteristic deflection”, which is a bridge (health) condition indicator used by the bus monitoring system, in damage detection. Sensitivity of “characteristic deflection” is verified by introducing artificial damage into a bridge that has ended its service life and is awaiting removal. As the results, it will be able to make a rational long-term health monitoring system for existing short and mediumspan bridges, and then the system helps bridge administrators to establish the rational maintenance strategies.展开更多
The fiber optic technology has matured to the point where Metropolitan Area Networks(MAN)can be built to operate at speeds from 150Mbps to more than 1Gbps.This paper in-troduces an experimental fiber optic MAN.The top...The fiber optic technology has matured to the point where Metropolitan Area Networks(MAN)can be built to operate at speeds from 150Mbps to more than 1Gbps.This paper in-troduces an experimental fiber optic MAN.The topology of this MAN is an open looped dualbus,and the data rate at each bus is 155.520 Mbps.We apply ATM technique and modified802.6 DQDB MAC protocol,using universal packet switching.The cell format is completelycompatible with B-ISDN cell.Through gateway the MAN can be interconnected with theBroadband Data Microwave Network,VSAT,Satellite Broadcast TV System,and Ether-net.There are up to 254 nodes connecting to the network,and the distance between two ad-jacent nodes covers more than 5 kilometers.We use 1.3μm SMF as the transmission medi-um.This paper emphasizes on the design and implementation of the Medium Access Control(MAC)Protocol.展开更多
文摘Largest portion of the bridge stock in almost any country and bridge owning organisation consists on ordinary bridges that has short or medium spans and are now deteriorating due to aging, etc. Therefore, it is becoming an important social concern to develop and put to practical use simple and efficient health monitoring systems for existing short and medium span (10 - 30 m) bridges. In this paper, one practical solution to the problem for condition assessment of short and medium span bridges was discussed. A vehicle-based measurement with a public bus as part of a public transit system (called “Bus monitoring system”) has been developed to be capable of detecting damage that may affect the structural safety of a bridge from long term vibration measurement data collected while the vehicle (bus) crossed the target bridges. This paper systematically describes how the system has been developed. The bus monitoring system aims to detect the transition from the damage acceleration period, in which the structural safety of an aged bridge declines sharply, to the deterioration period by continually monitoring the bridge of interest. To evaluate the practicality of the newly developed bus monitoring system, it has been field-tested over a period of about four years by using an in-service fixed-route bus operating on a bus route in the city of Ube, Yamaguchi Prefecture, Japan. The verification results thus obtained are also described in this paper. This study also evaluates the sensitivity of “characteristic deflection”, which is a bridge (health) condition indicator used by the bus monitoring system, in damage detection. Sensitivity of “characteristic deflection” is verified by introducing artificial damage into a bridge that has ended its service life and is awaiting removal. As the results, it will be able to make a rational long-term health monitoring system for existing short and mediumspan bridges, and then the system helps bridge administrators to establish the rational maintenance strategies.
文摘The fiber optic technology has matured to the point where Metropolitan Area Networks(MAN)can be built to operate at speeds from 150Mbps to more than 1Gbps.This paper in-troduces an experimental fiber optic MAN.The topology of this MAN is an open looped dualbus,and the data rate at each bus is 155.520 Mbps.We apply ATM technique and modified802.6 DQDB MAC protocol,using universal packet switching.The cell format is completelycompatible with B-ISDN cell.Through gateway the MAN can be interconnected with theBroadband Data Microwave Network,VSAT,Satellite Broadcast TV System,and Ether-net.There are up to 254 nodes connecting to the network,and the distance between two ad-jacent nodes covers more than 5 kilometers.We use 1.3μm SMF as the transmission medi-um.This paper emphasizes on the design and implementation of the Medium Access Control(MAC)Protocol.
