Warning Methods For Performance Abnormality Of Bearings Of Long-Span Bridges Driven By Monitoring Data

For bearings of a long-span bridge,its damage occurs frequently,such as peeling-off and wear of the sliding plate in sliding bearings,and failure of tension pendulums.The service life of bearings is very short and the maintenance is expensive.It will affect the safety of bridges if the bearing is damaged.Early warning for bearings of a long-span bridge,using the long-term monitoring data obtained by a bridge health monitoring system,is of great significance to ensure the safe operation of the bridge.A study on performance abnormality warning of bearings of long-span bridges driven by monitoring data was conducted for four main problems:the large prediction error of static bearing displacement model,the lack of methods to monitor the change in the sliding friction of sliding bearings,the inaccurate cumulative sliding displacement obtained by bearing displacement monitoring,and the lack of a method to monitor the tensile pendulum damage of uplift-restraint bearings.The main research contents and results are as follows:(1)An early warning method was established for the abnormal and out-of-bounds conditions of the bearing displacement based on a novel time-varying temperaturedisplacement model.Abnormal and out-of-bounds bearing displacements imply the performance degradation of bridges.The common temperature-displacement models ignore the influence of time-varying non-uniform temperature field on the model error.However,the relatively large model error will cover the abnormal amount of static displacement caused by structural performance changes.Therefore,based on the linear temperature-displacement relationship,a novel time-varying temperature-displacement model was first proposed by analyzing the relationship between structural time-varying non-uniform temperature and static bearing displacements.Then,early warning methods were established for the abnormal and out-of-bounds conditions of the bearing displacement based on the displacement prediction error.Furthermore,a hierarchical early warning was proposed according to the different combinations of early warning ratios.Additionally,the implementation step of the hierarchical early warning was given.The results of a case study show that the proposed time-varying model is more accurate than the common model.Additionally,the bearing with relatively large model errors will correspond to a relatively high warning level in each case.(2)An early warning method for abnormal bearing sliding friction was established using the proposed temperature-displacement hysteresis model.The increase in sliding friction of a sliding bearing means the peeling-off and wear damage of the bearing,which will affect the safety of a bridge.However,there was a lack of effective early warning methods for the increase in sliding friction of bearings of long-span bridges.Therefore,taking the influence of sliding friction on the bearing displacement caused by structural temperature into account,a temperature-displacement hysteresis model was first proposed.Following the extraction of a monitoring index reflecting sliding friction,an early warning method for abnormal bearing sliding friction was established using the cumulative sum control chart;and the implementation process of the early warning was systematically described.The results of a case study indicate that the proposed temperature-displacement hysteresis model can reflect the bearing sliding friction.The early warning method for bearing sliding friction can effectively detect the increase in the bearing sliding friction.(3)An early warning method was established for the wear of sliding bearings using a proposed estimation approach of the cumulative displacement(mode rotation angle superposition approach).Sliding bearings will have sliding failure if the replacement is not in time during serious wear of the bearing.However,the influence of the dynamic displacement accumulation with relatively high frequency on the wear of the bearing was not fully considered in the related research,resulting in underestimation of the wear condition of the bearing.Therefore,the estimation approach of cumulative displacement using the acceleration data of a girder was first proposed for sliding bearings by analyzing the bearing sliding displacements caused by deformation of main girders and the relationship between the displacement components under dynamic load.Then,a calculation method of the remaining sliding disk thickness was proposed for the early warning of sliding disk wear,followed by the implementation process of the early warning method.The analysis results indicate that the proposed estimation method for cumulative sliding displacement has acceptable accuracy and good noise robustness and can compensate for the drawback of low-sampling-frequency displacement sensors in calculating cumulative displacement.The early warning method can effectively predict the sliding disk wear of bearings.(4)Early warning methods for the damage to tension pendulums of uplift-r-estraint bearings were proposed using the vertical displacement ratio and structural frequency variance.The failure of tension pendulums of uplift-restraint bearings results in the change of the structural system of long-span bridges,which seriously threatens the safety of the bridge.However,there was a lack of early warning methods for damage to the tension pendulum.Therefore,two early warning methods for the damage were proposed.I:By introducing the area reduction factor of tension pendulums and eliminating the influence of the vehicle weight on the displacement index,the vertical displacement ratio was proposed as a warning index for the tension pendulum damage.Then,the changing mode of the warning index was analyzed theoretically under different damage conditions when a vehicle passes in different lanes.The results indicate that the early warning index obtained when vehicles pass through the outermost lane of a bridge possesses the best warning effect.?:The sensitivity of vertical bending frequencies of cable-stayed bridges to the area reduction of the tension pendulum was derived theoretically.By analyzing the cases in which the tension pendulum damage can be reflected by the frequency index,an early warning method for the tension pendulum damage was proposed using the variance in the bending mode frequencies.The results of finite element simulation and case study indicate that the frequency variance of vertical bending mode caused by the damage of tensile pendulums has the characteristics of large fluctuations,a gradual decrease in the minimum value,and a significant reduction.The early warning method based on the variance of the vertical bending frequency is feasible.