RAILWAY-LOAD EFFECTS ON A COMBINED HIGHWAY AND RAILWAY SUSPENSION BRIDGE

摘要

A Wind And Structural Health Monitoring System (WASHMS) for Tsing Ma Bridge has been devised,installed and operated by Highways Department of the Government of Hong Kong Special Administrative Region (HKSAR) since 1997. The WASHMS is devised to carry out the monitoring of four categories of parameters, namely, environmental status, traffic loads, bridge features and bridge responses. The bridge responses include time-series data of acceleration, displacement, and strain/stress from accelerometers, Global Positioning Systems (GPS) and dynamic strain gauges respectively. These bridge responses are however induced by a combination of four major types of load effects during a typical monitoring period. The four major types of load effects are referring to wind, temperature, highway, and railway loads. In order to carry out railway-load effect evaluation, it is therefore necessary to extract the response due to railway-load effects from the combined responses.In this regard, different procedures are adopted to extract those responses contributed by railway-load effects from the combined responses through the usage of wavelet packet transform and engineering considerations. The extracted railway-induced responses of displacement and acceleration in bridge deck are then analyzed to ascertain the railway-load effects on the bridge. The extracted railway-induced responses of time history of strains/stresses are finally analyzed to estimate the remaining fatigue life of the related bridge components based on the Miner's law. The analyzed results show that the railway load plays a predominant effect on the vertical displacement of the bridge deck compared with highway load, while the effect of railway load is less significant on the vertical acceleration of the bridge deck. The fatigue damage induced by train is much larger than that induced by truck and the fatigue life of Tsing Ma Bridge is long and it is in very good condition.