Vibration Response And Damage Analysis Of Cable-stayed Bridges With Lower Towers Under Earthquake Excitation

Concrete is a common material used in the modern civil engineering. Thereasonable anti-seismic design method is vital to prevent earthquake disasters. It isalso a basis to find the effective anti-seismic ways.Damage degree of reinforced concrete bridges structures would rapidly increase in avery short time with the application of the seismic loads, and the loading capacity ofstructures would loss partly or completely. If the damage effect of concrete material isnot considered, the results from the traditional structural dynamics are oftenunsatisfactory, especially in the period near the structural failure. By the considerationof damage effect of concrete material, the theoretical analysis accuracy would beincreased, especially for the analysis of the complicated non-linear behaviors near thestructural failure. The development of damage theory for concrete structures canprovide a scientific basis for the structural dynamic analysis, the safety assessmentand reinforcement design. The deep investigations for the damage failure problems ofreinforced concrete structures have the significant scientific meaning and engineeringapplication value.The damage mechanisms of concrete material are investigated in this work. Severalcommon damage constitutive models are discussed and compared. The general elasticdamage theory based on the strict irreversible dynamics is employed, and then thelimitations of the traditional damage theory are overcome. By taking the second-orderform of the general elastic damage theory, a practical concrete damage constitutivemodel is then developed. The main work in this thesis is listed in the follows.(1) The classical damage theories are introduced. The description of concretedamage mechanisms is discussed. The research approaches of damage mechanics areintroduced. The limitations of classical damage theories are indicated. In addition, thekey points of damage theory based on the strict irreversible dynamics are explained.(2) Finite element analytical model of Xijiang Large Bridge (a cable-stayed bridgewith low towers) is established by using the commercial software ANSYS. Thedynamic characteristics analysis is then performed. The vibration modes are obtained.The influence factors for the dynamic characteristics are discussed. (3) According to the location of Xijiang Large Bridge, the maximum seismicintensity is prescribed. The time-history response analysis under the seismic excitationis performed. The corresponding seismic wave that cause the structure failure and thestructural failure location are then determined.(4) By using the commercial software ABAQUS, the3-D FEM model for the mainpier is established. The damage constitutive model is introduced into the softwareABAQUS. The damage evolution history of the main bridge pier under the seismicexcitation is numerically simulated. The anti-seismic characteristics of the bridge areassessed according to the numerical simulation results. The result by this work can betaken as a useful reference for the anti-seismic design for ones similar to this bridge.