Research On Vibration Analysis And Safety Evaluation Of Hangers In A High-speed Railway Long-span Arch Bridge

With the rapid development of the high-speed railway in our country,the operating safety of the high-speed railway bridges has been gradually concerned by many scholars at home and abroad.Due to the high load and speed of the high-speed railway trains,the vibration response of the bridge is significant,especially for the hanger of the arch bridge,which will cause obvious vibration response and the vibration fatigue.The safety and durability of the arch bridge structure is directly affected by the safety of the hanger.Therefore,the vibration fatigue of the arch bridge hanger is one of the main diseases of the arch bridge,and it is necessary to carry out long-term vibration monitoring and safety assessment for the hanger of a special bridge type like Dashengguan Bridge.Based on the hanger of NanJing Dashengguan Bridge,this paper investigates the vibration response of the long hanger under high-speed trains and temperature.Moreover,the fatigue characteristics of the short hanger under high-speed trains are discussed.The main contents and achievements in this paper are as follows.1.Based on the long-term monitoring data of vibration velocity,the vibration response of the long hanger under high-speed trains is analyzed,the method of the degradation monitoring of the long hanger's vibration performance is put forward.The results indicate that:(1)It is difficult to establish an effective correlation model between the vibration amplitude of the long hanger and the train speed to characterize the long hanger's vibration performance when a train passes.(2)With the same load(i.e.,the same carriage number),the vibration amplitude in load cases close to the hanger are bigger than those in load cases far away the hanger.The long hanger's longitudinal and transverse amplitudes are less affected by the structural temperature.(3)The log-logistic distribution function can describe the probability density statistics of the long hanger's vibration amplitude.On this basis,the t-test method is used to analyze degradation monitoring of the long hanger's vibration characteristic.2.Based on the long-term monitoring data of vibration speed under environmental excitation,the vibration amplitude and frequency of the long hanger are analyzed.On this basis,the method of the degradation monitoring of the long hanger's vibration performance is put forward.The results indicate that:(1)The long hanger's longitudinal and transverse amplitudes are less affected by the structural temperature.(2)The generalized extreme value distribution function can describe the probability density statistics of the vibration amplitude of long hanger under the temperature.On this basis,The transcendence probability of the vibration amplitude of long hanger can be obtained directly,and thus set the safety warning threshold of the vibration amplitude of long hanger.(3)There is a strong correlation between the natural frequency of long hanger and structure temperature,which presents the performance of the "high temperature low temperature,low temperature high temperature".The environmental normalization of frequency is obtained by eliminating the influence of the structural temperature.On this basis,the mean control graph method can be used to identify the abnormal change of long hanger's frequency.3.Based on the long-term monitoring data of strain,the fatigue characteristics of short hanger under high-speed trains are analyzed.The results indicate that:(1)the axial strain maximum,the bending strain maximum and the axial-bending effect coefficient of the short hanger are not correlated with the train speed respectively.But they are related to the carriage number of the train and the driving lanes,The high-speed train runs the lane closer to the short hanger,the more the number of trains,the greater the fatigue damage caused by the short hanger.(2)The equivalent stress amplitude which considers the shaft-bending strain is larger than the equivalent stress amplitude which only considers axial strain,so it is important to consider the effect of bending strain increase effect on fatigue damage research.Considering that the annual fatigue damage under axial-bending strain is obviously larger than that under axial strain only.(3)With the same lane,the more the number of trrains,the greater the fatigue damage.However,the high-speed trains which is under the different lanes have a greater impact on the fatigue damage of the short hanger in load cases close to the short hanger.The results provide an important basis for the follow-up design and maintenance of the short hanger's fatigue.