Static And Aseismic Behavior Of Large Span Half-Through CFST Arch Bridges

Concrete-filled steel tubes (CFST) are widely used in arch bridges due to their high compressive strength and span by itself in construction. The development of CFST arch bridges has been limited by the code absence of design and construction of CFST arch bridges at home and abroad, as well as the existing arch bridge codes are only applicable to bridges with the span less than 200m. Therefore research on static and aseismic behavior of large span CFST arch bridges becomes very important to both theoretical analysis and practical application.In this paper, research on static and aseismic behavior of large span half-through CFST arch bridges is carried out with commercial ANSYS. The main research contents are as follows:(1) According to CFST Unified Theory, material property of CFST arch ribs is specified. With detailed introduction of the element types and techniques adopted, a three-dimensional finite element model of a large span half-through CFST arch bridge is built.(2) Detailed study of influences of main parameters such as load cases, f/L (rise-to-span ratio), inclination angle and lateral braces, on natural vibration characteristic and elastic stability coefficients of large span half-through CFST arch bridges are investigated. With the integration of natural vibration analysis and elastic stability analysis, it can be concluded that the elastic coefficient has different development tendency with the natural frequency after considering both dynamic characteristics and elastic stability. Therefore there are more to consider than to judge structural parameters simply on the basis of natural vibration analysis.(3) The whole failure process of the large span half-through CFST arch bridge under design load is studied with the consideration of both geometric and material non-linearity. The purpose is to analyze the whole bridge model and simplified arch model. In the former case, the loads are applied on the deck; in the later case, the loads are applied on the arch ribs as concentrated forces on hangers. The analysis shows that the large span half-through CFST arch bridge generally attains limit stability failure under design load. Non-conservative forces contribute greatly to both the in-plane and out-of-plane stiffness of the bridge, which will increase the load-bearing capacity of the structure dramatically. Elastic stability coefficient (λ) is greater than elastic-plastic one (λcr) obviously because of nonlinear factors. The ratio ofλ/λcr should not be considered as constant value during design.(4) Elastic time-history analysis of the large span half-through CFST arch bridge under frequent-encounter earthquake is carried out. Influences of geometric non-linearity, earthquake input dimensions, wave travel effect and main structural parameters on seismic responses are analyzed. It is advised that geometric non-linearity should be considered during the aseismic analysis of CFST arch bridges with span over 300m. When wave travel velocity changes between 50m/s-500m/s, influence of wave travel effect on structural seismic response changes with ground conditions, spectral characteristics of the earthquake, dynamic characteristics of the structures; When travel velocity exceeds 1200m/s-1500m/s, the influence decreases and structural response gradually approaches to that one obtained under coincident excitation.(5) Elastic-plastic time-history analysis of the large span half-through CFST arch bridge under severe earthquake is accomplished. According to node displacement of arch rib, displacement ductility factor, strain energy and plastic strain energy, the whole structural failure procedure under severe earthquake is analyzed; the failure mechanism and the structural modes are discussed. It can be concluded that the shape displacement and plasticity development are the main reasons leading to the dynamic failure of the large span CFST arch bridges under severe earthquake. Consequently, multiple response indexes should be used to evaluate the aseismic behavior of the large span CFST arch bridges.