Research On Identification Of Time-varying Cable Forces Of Cable Supported Bridge

Cables have been widely used in the construction of cable supported bridge due to their light weight and high strength mechanical properties.As the key component of cable supported bridge,the internal force state of the bridge structure is affected by the cable force directly.In the process of pulling the cable,it is necessary to measure the cable force accurately,and control the change of the cable force to ensure that the shape and internal force distribution of the structure meet the design requirements.In the process of bridge operation,the cable tension will change under live load.By monitoring the cable force,the operating status of the bridge structure can be understood in time.During the cable replacement process,the cable force of adjacent cables changes very drastically,so the cable force changes during the replacement process need to be monitored in real time to ensure the safety of the structure.Therefore,realtime monitoring of the time-varying cable force of cable is very important for the construction,operation and maintenance of long-span bridges.Based on the time-frequency analysis method of multisynchrosqueezing transform,a new identification method of time-varying cable force is proposed.The main research content is developed from the following aspects:(1)The theory of time-varying modal parameter identification based on time-frequency analysis method is studied.The time-frequency distribution of vibration response is obtained by using multisynchrosqueezing transform.The instantaneous frequency component is extracted from the time-frequency distribution by ridge extraction algorithm.Finally,the various displacement components of the vibration response are obtained through signal separation and reconstruction.Meanwhile,the advantages of time-frequency analysis method based on multi synchronous compression transform are verified by using simulation signal.(2)The vibration characteristics of cable under time-varying cable force are studied.The dynamic equation of the cable under the action of time-varying cable force and its approximate solution are described,and the relationship between the time-varying cable force and the instantaneous natural frequency is obtained.Finally,the relationship between the instantaneous frequency of the cable’s vibration response and the instantaneous natural frequency of the cable itself is derived by using the Hilbert transform.(3)The accuracy of the proposed method under different cable force changing conditions is studied.In actual engineering,there will be noise influence when signal is collected,and the recognition accuracy of time-varying cable force under noise conditions with different signalto-noise ratios is studied.At the same time,the influence of the excitation position and sampling position on the recognition result is studied.Useing finite element software to simulate the time-varying cable force when the vehicle crosses the bridge,and the time-varying cable force is identified by the proposed method.Finally,the proposed method is used to identify the timevarying cable force under the bridge operation state.(4)In order to apply the proposed method to practical engineering,a program of timevarying cable force identification is designed based on Matlab graphical user interface.