Dynamic Stability Performance Of Concrete-filled Steel Tube Arch Bridges

Concrete-filled steel tube(CFST)arch bridge is widely used in engineering practice due to its beautiful linear shape,excellent spanning capacity,large stiffness-mass ratio and ease of construction.With the breakthrough of key design technology and erection technology of CFST arch bridges,the span length of arch bridge constructed shows an overall increasing trend.The arch rib structure tends to be slender and flexible,and its stability has become a key factor in restricting the span development of arch bridges.In terms of practical engineering,the load type of CFST bridge structure is mostly dynamic load.However,compared with the static stability problem,the stability of the arch bridge under dynamic load is rarely taken into consideration,and there are no relevant provisions have been provided in the industry standard and specifications.Against this background,the in-depth theoretical research on the dynamic stability of CFST arch bridge has a clearer engineering background and practical significance.In this paper,the long-span CFST arch bridge is taken as the research background,and a series of theoretical studies on the dynamic stability behaviour of arch bridge under time-varying load are carried out by using a combination of methods such as theoretical model derivation,numerical simulation and software development.The purpose is to propose an effective dynamic stability analysis method for long-span CFST arch bridges.The influence mechanism of the long-term effect of the core concrete on the dynamic stability of the bridge is mainly discussed,and the influence of the time-varying nondirectional force of the hanger on the long-term dynamic stability is analyzed.The main content and conclusions of this paper are as follows:(1)Aiming at the application limitation of active confined concrete strength model for high strength concrete,a novel strength prediction model for active confined concrete is established in this paper and the uniaxial constitutive model is developed on Open Sees platform.According to the nonlinear stability analysis theory and the characteristics of CFST structure,a refined numerical method for structural stability analysis is established to reveal the instability mechanism of CFST arch structure under different load conditions.The established method provides the necessary theoretical basis for subsequent dynamic stability analysis.(2)Combining the relationship between structural static and dynamic instability characteristics,according to the instability mode differences of CFST arch structure under different working conditions,a dynamic stability identification method and analysis process suitable for any dynamic load form are proposed.Taking seismic station test of a scaled arch as an example,the seismic stability analysis is carried out.The analysis results verified the applicability of the proposed dynamic stability criterion.According to the proposed dynamic stability analysis method,the sensitivity analysis of material parameters,geometric parameters and structural parameters of arch ribs under seismic load is carried out by using the numerical analysis strategy of recursive algorithm.(3)Based on Mathieu-Hill equation,using Galerkin method and Bolotin excitation theory,the main and secondary unstable parametric vibration regions of CFST arch are derived under the dual nonlinear conditions of axial compression and coupled compression and bending.The theoretical model and analysis method of parametric stability of CFST arch rib under periodic load are established,and the effects of damping and in-plane symmetric vibration are considered.The parametric vibration analysis of an existing CFST arch bridge is carried out,and the possible parametric vibration working conditions are given as well.The derived instability interval is compared with the main instability region determined by the energy criterion,and the applicability of the proposed analytical model is verified.(4)Based on the progressive integral creep algorithm,the secondary program development of the shrinkage and creep algorithm of concrete was completed based on the ABAQUS calculation platform,and the creep aftereffect tests of the corresponding CFST short columns and arches were compared and analyzed to verify the effectiveness of the proposed algorithm.Taking Yajisha Bridge as an example,the seismic time history analysis was carried out.The influence and mechanism of long-term effect of core concrete on the performance evolution of CFST composite section and the influence on dynamic stability were studied and discussed.Moreover,the state of the whole bridge after the earthquake was evaluated.The influence of seismic wave input mode,traveling wave effect and concrete pouring sequence on the dynamic long-term stability of CFST arch bridge is discussed.(5)In view of the difference in the mechanism of the non-conservative force of the suspender in the static and dynamic conditions,a physical index and quantitative analysis method are proposed to define the level of influence of the non-conservative force effect on the spatial stability of the CFST arch bridge.The influence of the time-varying nonconservative force effect of the suspender on the transverse deformation and long-term dynamic stability of the CFST arch bridge under different structural frequency,load excitation frequency and connection stiffness are analysed.This provides a reference for the dynamic stability design of the arch bridge in the future.