Damping Characteristics And Seismic Performance Of Partial Cable-stayed Bridge

As a new bridge structure, the negative impact of structural damage and collapse of partial cable-stayed bridge is extremely large, because of its complex mechanical system and large project investment. Therefore, it's necessary to study this kind of bridge in-depth.Vibration and damping characteristics is an important aspect to reflect the structure properties, and has very important significance on researches of seismic design, wind-resistant design, coupled vibration and damage identification. Through theoretical and experimental analysis, vibration and damping characteristics is investigated in-depth for PC partial cable-stayed bridge with tower beam consolidation and pier beam separation. In addition, seismic performance of this bridge is studied, because of specificity of large bearings under towers.First, this thesis outlines the development of partial cable-stayed bridge, structural features, and research status at home and abroad. Then it introduces the vibration theory of bridge, the finite element equations considering cable local vibration, damping theory, modal damping identification method (ERA), and calculation of seismic response. On this basis, taking a bridge crossing Jinghang Canal in Kangqiao Road of Hangzhou as an example, the effects of cable local vibration and ground deformation on structural dynamic characteristics are investigated. According to the results of two vibration tests, modes and modal damping ratios are identified using ERA. The applicability of non-orthogonal damping theory and strain energy proportional damping theory is discussed. At last, seismic responses of structure are studied. Some conclusions of this paper are as follows:(1) The effects of cable local vibration on main modes of PC partial cable-stayed bridge are very limited, while ground deformation has significant effects on longitudinal floating mode and lateral bending mode. (2) The average of measurements of modal damping ratio of PC partial cable-stayed bridge is around 1%, which is consistent with foreign measured data. And the results demonstrate again that the modal damping ratio of partial cable-stayed bridge is less than continuous beam bridge.(3) The modal damping ratio can be obtained by superposition of component damping under small damping condition. It also can be approximately estimated with strain energy proportional damping theory, while the material damping ratios of PC beam, concrete pier and tower and steel cable are around 1.0%,1.2%,0.1% and 4.0% respectively. The modal damping ratio can be obtained by superposition of component damping with either strain energy proportional damping theory or non-orthogonal damping theory, but the contribution of components to modal damping ratio is quite different.(4) Maximum of plane bending moment of beam is located in the main pier, and longitudinal displacement of the top of pier with fixed bearings is more significant and the design should have certain safety margin. Value of seismic response of cable tension is small relative to initial cable tension, and has little effect on the seismic safety of structure. Vertical earthquake loading is also small relative to the reaction force under dead load. The level earthquake loading is major passed to the main pier with fixed bearings, and has some influence on the seismic performance of structure.