Evaluation Of Load Transfer Capacity Of Beam Bridge Transverse Connection Based On Modal Test

The assembled girder bridge is one of the more widely used bridge types for small and medium span highway bridges in China because of its advantages of easy prefabrication,economical material use,easy transportation and lifting.However,with the coupling effects of material aging,environmental erosion,long-term effects of loads,and fatigue effects,the transverse links between the main girders produce damage,which seriously affects the structural force integrity of the bridge.Therefore,the inspection and evaluation of the transverse linkage load transfer performance of the girder bridge and the actual load-bearing stiffness of the main girders,and the phased grasp of the evolution of the structural damage are of profound significance to ensure the safe operation of the bridge.This thesis takes assembled girder bridges,which are widely used in bridge engineering,as the object of study.Research was conducted on the identification of modal flexibility of bridges,the localization of transverse link damage of girders and bridges and the assessment of transverse link load transfer capacity,and a series of problems in assessing the transverse link load transfer capacity of girders and bridges based on environmentally stimulated modal testing were discussed,and the main work and results include the following.(1)Study of dynamic characteristics of bridges under vehicle loads.Focus on the analysis of the vehicle mass,vehicle stiffness and the vehicle’s action position on the frequency of simple-supported girder bridge influence law.The effect of vehicle action on bridge frequency is related to the vibration characteristics of the vehicle itself and the location of the action.The vibration frequency of the vehicle is less than the no-load state of the bridge in a certain order of self-oscillation frequency,the role of the vehicle will lead to the bridge under load state of the order frequency and higher order frequency becomes larger.The vibration frequency of the vehicle is greater than the self-oscillation frequency of a certain order of the bridge under no-load condition,and the action of the vehicle will cause the order frequency of the bridge under loaded condition as well as the lower order frequency to become smaller.The vehicle acts on the location of the maximum modal amplitude of the bridge,which has the most significant effect on the order frequency,and the vehicle acts on the location of the zero amplitude of the modal amplitude,which has no effect on the order frequency.(2)Identification of transverse linkage damage in girder bridges based on modal testing.The sensitivity of damage identification indexes such as frequency,displacement vibration pattern,displacement flexibility matrix and load transverse distribution influence line of simply supported hollow slab beam bridges was investigated.Low-order frequencies reflect the overall performance of the structure,and the damage to the hinge joints cannot be accurately identified by the change in bridge frequency alone.The vibration and modal displacement flexibility matrix of the structure can locate the damage between the side beam and the secondary beam,but for the damage between the hinge joints of other main beams,the exact location of the damage cannot be accurately located.In the case of damage to a single hinge joint,the crossover phenomenon of the influence lines of the transverse distribution of each main beam load at the location of the damage can be used to effectively identify the location of the weakness,with simple and intuitive features.(3)Identification of modal flexibility of bridges based on parked vehicles and analysis of influencing factors.The selection of the modal order in the modal test of the simply supported girder bridge and the selection of the key locations of the sensor measurement points are determined.Treating the vehicle as a flexible applied mass facilitates the additional mass method for scaling bridge vibration patterns.The sensor measurement points are placed only at the mid-span position of the main beam,and the first three orders of measured vibration patterns are scaled by means of standing.It is able to accurately identify the modal displacement flexibility matrix at the mid-span position of a simply supported girder bridge,and then predict the modal deflection of the bridge at the mid-span of the main girder under static loading.The number of sensor measurement points is greatly reduced,and the test process is faster and more convenient,saving time and effort,with a low error rate.(4)Assessment of transverse link load transfer capacity and main girder load carrying stiffness of small and medium span girder bridges.Using the difference between the modal deflection of each main girder and the original bridge design deflection,it is possible to make a preliminary determination of the lateral deflection distribution state of each main girder.The sudden change in the relative modal deflection between adjacent main girders under Off-loading enables the identification of weak transverse links in simply supported girder bridges.Weak transverse connections at the damage location and the discounted modulus of elasticity of the main beam,poor connection performance of all parts of the structure,relatively low safety reserves,and generally larger deflection calibration coefficients of the main beam on both sides of the damage location compared to other main beams.The magnitude and trend of the modal deflection calibration coefficients in the cross-bridge direction of each main beam can scientifically and accurately assess the load transfer capacity of the transverse links and the actual load-bearing stiffness of the main beam.