Study On Vibration Frequency Identification Method Of Existing Medium And Small Span Railway Bridges

With the development of heavy load capacity expansion and reconstruction of existing freight railways in China,the load effect of small and medium-sized span bridges increases obviously,and the main girder gradually appears cracking,stiffness degradation and frequency decline.The vibration frequency of the bridge is the important parameters of the dynamic characteristics of bridge evaluation and damage identification,but for small and medium span railway bridges,due to its large natural frequency value and high stiffness and boundary conditions is not clear wait for a characteristic,through traditional methods such as the spectrum method of modal parameter identification,the peak in the spectrum and more close,frequency of structure is not easy to identify.In this paper,we study the cross-power spectrum method is adopted,the steady state diagram method and frequency domain decomposition method for drawing number for the "1024" bridge of 8 m ordinary reinforced concrete low altitude plate girder bridge and figure number is "(96)2066" bridge of 16 m prestressed concrete T beam bridge has carried on the modal parameter identification,and based on the ANSYS finite element calculation software has carried on the sensitivity analysis to the finite element model and model modification.The main research contents and conclusions are as follows:(1)In the case of ambient pulsating excitation,the speed signals of 8 m,16 m and 32 m railway bridges were collected,and the first-order natural vibration frequency of the bridge was identified and analyzed by using the cross-power spectrum method.The results show that the identification process of cross power spectrum method is complicated,and it is not suitable for railway bridges under 16 m under the condition of pulsation test.(2)Under the circumstance of the pulsating excitation,the velocity signal of the steel beam with length of 4 m was collected,and then the steady-state diagram method and frequency domain decomposition method were used to identify the first-order natural vibration frequency of the test beam.Finally,the recognition results of the two methods were basically the same,which verified the feasibility of the two methods in identifying the vibration frequency of the structure.(3)Steady-state diagram method and frequency-domain decomposition method are used to identify the modal parameters of railway bridges under 16 m under environmental excitation.The results show that both the steady-state diagram method and frequency-domain decomposition method can accurately identify the fundamental frequency of the bridge,but the frequency-domain decomposition method is simpler and more widely applicable than the steady-state diagram method.(4)Based on the finite element model of physical parameters sensitivity analysis found that the phase ii of bridge deck shop is added mass and girder concrete elastic modulus,density and quality of main girder concrete bearing transverse spring stiffness of each order frequency sensitivity is stronger,and bearing longitudinal spring stiffness and poisson's ratio of concrete girder of each order frequency sensitivity is weak.(5)Based on ANSYS finite element calculation software,the zero-order method and first-order method are used to comprehensively modify the finite element model.The modified finite element model more truly reflects the dynamic characteristics of the bridge,thus providing a more accurate reference finite element model for the later research work of bridge damage identification and safety assessment.