Analyses And Monitoring Of The Influence Of Non Uniform Settlement Of Pile Foundation To Bridge Superstructures

Since the pile foundation has a high carried capacity as well as good stability,its design theory and construction technology are mature and its applicability is strong,in addition,it is easier to transport and install.Pile foundation is widely used in bridge construction in permafrost regions.However,in permafrost regions,the change of temperature around pile foundation will reduce the shear strength of the pile and the surrounding soil interface.As a result of this change,the bearing capacity of the pile decreased and the displacement of the pile location increased,which threatens the stability of the bridge and traffic safety.Although,the uneven settlement of pile is directly related to the local damage and overall safety of the bridge,however,there is little attention to the stress change of bridge superstructure caused by the uneven settlement of pile foundation in domestic and abroad.The main contents of this paper are as follows:First,through field investigation,analysis,and historical observation data,the long-term non-uniform settlement data of different pile foundations of a simple girder bridge on Qinghai-Tibet plateau are obtained.On this basis,the uneven settlement of pile foundation is introduced into the analysis of the simply supported beam bridge upper structure,the finite element model based on the real bridge structure is established,and the stress,strain distribution and deformation of structures under different settlement modes are analyzed.The results show that the uneven settlement of pile foundation in permafrost regions will cause the stress concentration at the hinge joint of the bridge,which will lead to the transverse crack of the bridge.In addition,when the uneven settlement of pile foundation occurs,the unilateral settlement will lead to torsion deformation of the whole structure.Secondly,according to the above static analysis results,the cement mortar at the hinge joint of the bridge will be damaged under the condition of uneven settlement of pile foundation.Therefore,a finite element model considering hinge joint damage was established,and its modal analysis was carried out.The results show that the structure frequency and vibration modes change significantly when the local transverse connection is broken.Then,using modal confidence criterion and further coordinate modal confidence criterion on the damage of bridge damage identification research,the results show that the method can effectively identify and locate transverse connection damage.Subsequently,the damage identification of damaged Bridge is studied by using the Modal Assurance Criteria(MAC)and Coordinate modal assurance criterion(COMAC),the results show that the above method can identify and locate transverse connection failure.Finally,a sensor system for structural monitoring,including temperature,strain,and vibration sensors were designed for a real bridge on the Qinghai-Tibet plateau.The data collected are analyzed.The temperature data show that there is a significant temperature difference between two sides of the bridge due to the influence of sunshine and other factors.The analysis of strain data shows that the random distribution of vehicle load on bridge deck leads to different strain values measured by strain sensor.As can be seen from the strain data,when a vehicle passes through,the strain will have a large peak value,so the size and distribution characteristics of vehicle load can be obtained,and the speed and direction can be further analyzed.Finally,the acceleration data of the bridge is analyzed,and the fundamental frequency of the structure is determined to be between 5.6-5.8Hz and affected by external environments such as temperature and vehicle load.The above data provide basic information for subsequent structural damage identification and safety assessment.