Orthotropic Steel Deck Bridge Dynamic Response And Loads Identification Of Vehicles

Fatigue cracking is a common disease in orthotropic steel deck(OSD)bridges,which may deteriorate the safety of OSD bridges,and it attracts the world-wide concerns.The following aspects in fatigue design should be attributed to the issues:the specification may underestimate the vehicle dynamic impact factor for OSD bridges;the local stiffness of the steel deck pavement is low;the standard fatigue vehicle can not adequately reflect the actual traffic loads on OSD bridges;and the current fatigue assessment by fatigue design is not accurate enough.To improve the accuracy of estimating fatigue life and reduce the probability of fatigue cracking for OSD bridges,this dissertation focused on the following aspects.Firstly,a modelling method of establishing the vehichle-bridge interaction model applying to OSD bridges was presented.The author made a briefly theoretical analysis on vehicle dynamic mechenical performance of OSD bridges.Secondly,based on a New Engineering Structure of Guangdong Fochen Bridge(referred to:Fochen New Bridge,it contains two separate three-span continuous steel box bridges with orthotropic steel deck.One bridge adopts the conventional OSD using asphalt layer,another adopts the innovative Orthotropic Lightweight Steel-UHPC Composite Deck),a lot of field test have been conducted to investigate the static and dynamic mechanical performance of the traditional OSD and Orthotropic Lightweight Steel-UHPC Composite Deck.Finally,the author introduced bridge weigh-in-motion(BWIM)technique into the OSD bridges.BWIM was used to record dynamic response of OSD and indentify the silhouette of the vehicles(speed,axle spacings,axle weights and.etc)passing over the OSD bridges.The BWIM system proceeds a benefition to improve the fatigue design of OSD bridges.The main research contents are included:(1)Propose an updated vehicle-tire contact force model to simulate vehicle-bridge interaction,considering the tire contact area and the thickness of the bridge wearing surface.The author took a simply supported beam using multiple-point contact forcces as an example to analyze the effect of bridge dynamic performance by the tire contact area.To more accurately investigate the influence of the tire patch,a three-dimensional model of an OSD bridge was considered.The tire patch load was simulated by surface force.This modelling method provides theoretical basis to do intensive study on vehicle-bridge interaction applying to OSD bridges.(2)Using Fochen New Bridge as the object of study,the strain gauges were mounted at the fatigue-proned positions,and a series of static loading tests were conducted to make the comparison of mechanical performance between the two parallel separate bridges with traditional asphalt pavement and UHPC layer.Meanwhile,according to the design blueprint of Fochen New Bridge,a finite element model calibrated with measured data was established to simulate all loading cases of field test.The calculated results can be used as the theoretical basis for the follow-up study on OSD dynamic performance.(3)Using a 35t three-axle pre-weighed truck to pass through Fochen New Bridge of traditional asphalt pavement layer and UHPC layer repeatedly,the strain responses versus time at fatigue details were recorded,which were used to get dynamic strain range of each fatigue-proned detail by rain flow method.Combining the measured data and the corresponding calculated results,the dynamic impact factor at each fatigue-proned detail could be calculated,and the time domain and frequency domain analysis were done to find the modes that influence the OSD dynamic response.(4)Intall the Free-of-Axle-Detector(FAD)and weighing sensors in Fochen New Bridge with UHPC layer,drive a 35t three-axle calibrated truck pass over the bridge in Lane 2 repeatly,recording the strain responses versus time at each sensor.According to the latest BWIM algorithms,write the corresponding codes in Matlab to find axle weights.After comparing the accuracies of the selected BWIM algorithms,get the optimal BWIM algorithm applying to OSD bridges.(5)Propose an innovative bridge monitoring system,called Virtual Monitoring system.In this system,BWIM is used to get traffic information(include:axle spacings,alxe weights,loading transverse position and.etc).The strains at every point on the bridge can be calculated using the traffic information and the influence lines for these points.The influence lines can be got by bridge finite model.Hence,the fatigue life of every points on the bridge can be evaluated.The measure point at cutout in floorbeam on Fochen New was selected to investigate the concept of Virtual Monitoring.