Research On Static And Dynamic Characteristics Of Continuous Rigid Frame Low Pylon Cable-stayed Bridge With Double Thin-walled Piers

As a new type of composite system bridge,low tower cable-stayed bridges have rapidly emerged in recent decades.They have both the rigidity of continuous beam bridges and the flexibility of cable-stayed bridges.In terms of structural characteristics,the main beam of this bridge type has a greater stiffness,a smaller tower height,more concentrated stay cables,and a smaller spacing.When erecting bridges on land with strict requirements for bridge height,the small tower height makes low tower cable-stayed bridges a preferred choice.At the same time,in urban construction,the novel and beautiful shape of the low tower cable-stayed bridge has a broader use scenario.In recent years,earthquake disasters have become increasingly frequent in China,making bridge safety a top priority in transportation and its importance obvious.Therefore,the static and dynamic analysis and seismic design research of low tower cable-stayed bridges are extremely necessary,because the static and dynamic characteristics and seismic response analysis of bridges are the basis for seismic design research.In recent years,with the continuous increase in the number of completed low tower cable-stayed bridges,theoretical tests and research results of low tower cable-stayed bridges have emerged,and the construction technology has become increasingly sophisticated.However,research related to low tower cable-stayed bridges,such as static and dynamic characteristics and seismic response research,is not yet complete,and there is still little research related to double thin-walled pier continuous rigid frame low tower cable-stayed bridges.In this paper,there is a problem that the theoretical model lacks experimental evidence in the study of static and dynamic characteristics and seismic response analysis of continuous rigid frame low pylon cable-stayed bridges with double thin-walled piers.Taking the Weihe No.5 low pylon cable-stayed bridge(75+126+75)m,Gansu Tianshui International Inland Port Highway Bridge,as the engineering background,a large finite element calculation software Midas/Civil 2020 is used to establish a full bridge finite element model of the bridge,and the static and dynamic characteristics of the bridge are analyzed,The accuracy of the theoretical model is also verified using the experimental data of natural vibration characteristics.The research content can be summarized into the following three points:(1)Through the stress analysis of the main beam and main tower of a low tower cablestayed bridge,the internal force and stress distribution laws of the main beam and main tower under the maximum cantilever and completed bridge conditions are obtained,and the stresses of the main beam and main tower meet the requirements of the specification;The results of analyzing the cable force and stress amplitude of the stay cable satisfy the safety requirements;The variation law of cable force in different construction stages is obtained by analyzing the cable force in each construction stage;By analyzing the construction alignment of the main beam,the displacement of its dead load deformation and live load deformation is obtained,and the camber of the bridge is calculated,providing a theoretical basis for bridge deformation control;By analyzing the deformation of the main tower in each construction stage,the variation rule of the main tower displacement affected by each construction stage is obtained.(2)The dynamic characteristics of the finite element model are analyzed using the multiple Ritz vector method,and the effects of the stay cables on the natural vibration period and vibration mode characteristics of the background bridge and the differences in the effects of various locations of the bridge are studied.Based on the bridge site data and seismic design data,the response spectrum method is used to analyze the two-way seismic response of each model,and the effects of each bridge location on the response of the background bridge under seismic action are compared and analyzed.(3)Seismic loads do not maintain a certain acceleration on the structure along the longitudinal and lateral directions simultaneously,but often act on the structure at a certain angle.However,it is difficult to determine the input angle of ground motion.In this paper,the seismic response of the structure is simplified and calculated.The seismic load is applied to the entire bridge using a combination of longitudinal and vertical,lateral and vertical ground motions using consistent excitation.The peak acceleration of the vertical ground motion is0.65 times the horizontal direction.The nonlinear time history analysis results and the response spectrum results are checked against each other.(4)Analyze the isolation rate of ultra-high damping bearings on the internal force and displacement of the structure under frequent earthquakes and design earthquakes,and obtain that ultra-high damping bearings can effectively reduce the seismic response of the structure.