Research On Nonlinear Structural Dynamic Behaviors Of Long Span Cable-stayed Bridge With CFRP Cables

With the trend that the span of cable-stayed bridge becomes longer and longer, not only the cable corrosion and bearing efficiency but also the structural weight become increasingly prominent for the project of cable-stayed bridge. To replace traditional steel used in the cable, new material found as Carbon fiber reinforced composite (CFRP), which has the excellent characteristic of high strength, lightweight, anti-fatigue, corrosion resistance, etc, becomes a research hotspot. Using CFRP as cables of the long span cable-stayed bridge can not only take advantage of its high strength properties and solve the corrosion problems of the traditional steel cable, but also efficiently reduce the superstructure weight of cable-stayed bridge, improve the bearing efficiency of cable and get longer spanning capacity, so CFRP used as cable has a obviously competitive advantage. However, nonlinear dynamics system study of long-span CFRP cable-stayed bridge is hardly found at present. Analyzing the experiment study of the nation’s first CFRP cable-stayed bridge and the study of nonlinear dynamics theory, the paper explores the nonlinear dynamics performance and expects to provide scientific basis for the development and application of CFRP long span structure, which is based on the support of the National Natural Science Fund Project "CFRP prestress span structures (bridges and buildings) Nonlinear Analysis and Control (50678074)"and "Prototype design and related problems research of super long span bridge with high performance CFRP cables(51078170)". This paper completes the following tasks:(1)Nonlinear static and dynamic characteristics and parameter analysis of CFRP cableCompared with beam structure, cable considered as the main load-bearing component of cable-stayed bridges has the characteristics of light, soft and low damping, showing strongly nonlinear characteristics under the influence of cable droops. Based on catenaries element, the methods of analyzing dynamics and static characteristics are discussed according to the calculation theory of cable. What’s more, the methods are also applied to the dynamics and static characteristics and the parameter analysis of CFRP cable under different length and stress level and compared with the result of traditional steel cable. The results illustrate a series of meaningful conclusions.(2) Static experiment of CFRP cable-stayed testing bridge and finite element analysisTo analyze the static characteristics of the CFRP cable-stayed bridge, the paper studies static experiment on the CFRP cable-stayed footbridge, introducing both the main contents, methods of the experiment and establishing finite element model. Comparing related analysis results with the results obtained from experiment, basic data and the reference are provided for establishing the finite element model of long span CFRP cable-stayed bridge.(3) Mode experiment and dynamic characteristics analysis of CFRP cable-stayed testing bridgeBased on the static experimental data, mode experiment research is made in detail concerning the excitation mode, signal acquisition system, test methods, and test content and data processing etc. Then the mode experimental results are compared with those obtained from finite element dynamic analysis to confirm the dynamic characteristics of the CFRP cable-stayed bridge. Lastly, with regard to the dynamic characteristics and seismic response, the comparison between CFRP cable-stayed bridge and steel cable-stayed bridge with the same span is conducted.(4) Nonlinear dynamic characteristics and seismic response analysis of long span CFRP cable-stayed bridgeTwo finite element dynamic analysis models of cable-stayed bridges with the lkm main span are established. One cable is steel, the other is CFRP. The dynamic characteristics between them are compared. Based on time history analysis method, differences of seismic response time history and response peak are analyzed between long span CFRP cable-stayed bridge and steel cable-stayed bridge. The exploration to the seismic performance of long span CFRP cable-stayed bridge is discussed.(5) Seismic response control research of long span CFRP cable-stayed bridgeThe paper focuses on elastic connection and viscous damper selecting several objective functions such as longitudinal displacement at the end of the main beam, vertical displacement at the middle of the main span, longitudinal displacement on the top of towers, bending moment and axial force at the bottom of towers and internal force and deformation of seismic reduction devices. Based on the sensitivity analysis in both the parameters and the objective functions’values, the flexible connection stiffness k, damping coefficient C and speed index a are selected reasonably. At the same time, the effects of two measures for seismic response control applied in the two kinds of cable-stayed bridges are analyzed and compared.It is shown that the dynamic characteristics of CFRP cable and long span CFRP cable-stayed bridge differs from the steel cable and long span steel cable-stayed bridge. The natural torsion frequency of long span CFRP cable-stayed bridge has an obvious difference with the result calculated from specification. The Cable-stayed bridge with tower beam consolidation system, the possibility of torsion vibration mode is less likely to appear. Natural frequency of CFRP cable-stayed bridge is relatively higher than steel cable-stayed bridge under the same span condition. Seismic response peak value of CFRP cable-stayed bridge is relatively less than that of steel cable-stayed bridge. Seismic performance of CFRP cable-stayed bridge is superior to that of steel cable-stayed bridge. Meeting the same requirements of seismic response control, CFRP cable-stayed bridge has a lower requirement for design mechanic parameters than steel cable-stayed bridge. Under the same damper parameters, damping effect of the CFRP cable-stayed bridge is superior to that of steel cable-stayed bridge. The main research contents in this paper could offer theoretical basis and technical support to better and faster application of CFRP material in long span bridges or buildings.