Performance Evaluation And Damage Control Of Expansion Joints In Long-span Bridges

Damage in expansion joint is one of the most common problems in bridge maintenance,which may lead to considerable maintenance/replacement costs and influence on function of bridges.Therefore,analysis of damage mechanism and damage control are of great significance for damage detection,maintenance and replacement of expansion joints.Exisitng studies are focused on dynamic analysis based on measured data and numerical simulation.Suggestions have been put forward for the design and maintenance of key components of expansion joints under vertical vehicle loads.However,field inspection and preliminary analysis show that the horizontal cumulative displacements of the girders might be one of the reasons for the premature failure of expansion joints,and the small but high frequency displacements due to the vehicle/wind might contribute the majority of the cumulative displacement.Focused on the cumulative displacement of expansion joints,the fatigue failure of the expansion joints is investigated through numerical simulation,monitoring data analysis and fatigue tests in this paper.Reasons of premature failure of expansion joints are discussed in conjunction with the whole bridge structure and the internal structure of expansion joints,respectively,and suggestions were put forward for the damage control of the expansion joints.Based on the presented work,conclusions can be summarized as follows:(1)Based on the whole structure of the bridge,the influence of environmental load on the displacement of expansion joints is studied to seek for the macroscopic reasons of the premature failure.First,more realistic wind/vehicle load models are developed based on the monitored data.A displacement analysis method of expansion joints under bridge-traffic-wind coupled effect is proposed as well.The effect of vehicle speed,vehicle type,average speed of fluctuating wind and bridge-traffic-wind coupling on the displacement of the expansion joints is investigated.(2)The damage mechanism of expansion joints is studied from the internal structure of the expansion joints.First,a horizontal dynamic finite element model of the expansion joints is established.The response of lamellas and springs under static and dynamic displacements is studied through finite element analysis.It is found that the cumulative displacement of the lamellas is one of the reasons for the excessive wear of the sliding supports/control supports,and the unequal spring stress also leads to different damage condition of springs at different locations.(3)The monitored displacement data are analyzed and fatigue tests of springs were conducted.With the purpose of verifying the finite element analysis,the real displacement of the expansion joints and lamellas are monitored and compared with the simulated results.At the same time,shear fatigue tests of the springs were carried out to study the effect of fatigue displacement amplitude and failure mode on spring stiffness and fatigue life.(4)Finally,suggestions on the assessment and damage control of expansion joints are proposed.Influence of slip performance on the dynamic response of each component of expansion joints is studied.The relationship between the slip performance factor and the displacement ratio of the lamellas is also established to provide an easier method for evaluating the slip performance of the expansion joints.To this end,it is suggested that traffic control and viscous damper can be applied to control the damage of expansion joints,and mitigation effect of the two methods are evaluated.The above work have played an active role in the damage mechanism analysis and damage control of expansion joints of long-span steel bridges,which can also provide some references to the maintenance/replacement of expansion joints,so as to extend their service lives.