The Application Of Bridge Weight-in-motion System On Orthotropic Steel Decks

Orthotropic steel decks(OSDs)are widely used in various types of bridges owing to their advantages such as light weight,high capacity,and convenience in construction.Many OSD bridges were built over the last two decades in China,such as Humen Bridge,Sutong Bridge and Runyang Yangtze River Bridge.However,with the ever-increasing heavy traffic,especially overloaded vehicles,OSDs are inclined to premature fatigue cracking,which threatens the structural stability and leads to high costs of maintenance.In this case,the real-time monitor and control of heavy vehicles will be essential to the accurate safety assessment of OSD bridges.The recently developed bridge weigh-in-motion(BWIM)system has been proved to be an effective tool,using instrumented bridge as a large scale to identify axle weights and to figure out vehicle information(vehicle speed,axle numbers and spacing)in real time.This paper presents a BWIM system in which the longitudinal ribs of an orthotropic box-girder bridge are instrumented to identify axle weights of trucks.Based on the measured dynamic strains caused by the calibrated trucks,the ILs of the longitudinal ribs of OSDs(Orthotropic Steel Decks)are calibrated.With these calibrated ILs,the axle weights of moving vehicles crossing the instrumented ribs are identified.The live load stress in a rib can be viewed as the sum of two components,one due to the continuous beam function of the rib(simply referred to the local effect),and the other due to the main girder function of the bridge(referred to the global effect).To research the application of BWIM system on OSDs,a field test was conducted on the Fochen Bridge,a newly constructed OSD bridge,located in Guangdong,China.The idiographic work is as follows:(1)Deduce the algorithms of IL calibration and the identification of axle weights in detail.(2)Record the dynamic strains caused by the calibrated trucks repeatedly crossing over the two different sections of the bridge,one is in the pier of the middle span,called supported section;the other is near the quarter of the middle span,called L/4 section.Then calibrate the ILs of the longitudinal ribs of OSDs in these two sections.According to the analysis,the local effect in the supported section is more obvious,while the global effect is less significant.(3)Identify the axle weights of moving vehicles crossing the instrumented ribs with these calibrated ILs.The identified axle weights agreed with the static measurements,and the identified axle weights in both sections showed similar accuracy of results.(4)Through the analysis of the factors in axle weights identification,improve the accuracy of the BWIM system when applied to the orthotropic steel bridge.The results showed that:when the calibration vehicle is tested in a specific lane,it is recommended to select all the influence lines and then take the average of the ILs as the basis for axle weights identification;when the vehicle is crossing in a particular lane,it is advisable to select the influence line calibrated in this lane as the basis for the identification of the axle weights.Therefore,it is necessary to calibrate the ILs of all lanes.