Study On Seismic Response Nonlinear Time-History Analysis And Simplified Approach Of Self-Anchored Suspension Bridge

As the development of city bridge is changing to beautiful and long, the construction of self-anchored suspension bridge is more and more. To study on structure mechanics behavior and performance of this bridge structure is becoming hot point and the thesis that studies on seismic response of self-anchored suspension bridge is based on this background. Considering bridge structure as life-line and disastrous consequence after seismic and the current specified criteria to be not fit for analysis seismic of this style bridge, the thesis roundly analyzes current situation research of dynamic feature and seismic response and studies on resistance seismic analysis method of self-anchored suspension bridge in detail, and it summarizes recently-researched achievement of self-anchored suspension bridge free vibration and seismic response. Aimed at free vibration and structure response under seismic excitation of self-anchored suspension bridge, the thesis achieves differential equation of self-anchored suspension bridge free vibration, and under different excitation deep analyzes response of non-linear time-history, and brings forward simplified approach that analyzes seismic response of self-anchored suspension bridge. The chief research works of the thesis are as follows:(1) Application of generalized variation principle and classic analytical method, the thesis presents differential equation of self-anchored suspension bridge free vibration, and studies on boundary constraint conditions (such as connection of stuffiness girder, tower and side pier each other) affection to free vibration. Considering self-anchored suspension bridge characteristic, which is different to ordinary suspension bridge, synthetically taking into account longitudinal displacement of cable, coupling effect of stiffness girder axial and flexural action, shearing and ratio of rise to span etc., according to Hamilton principle, the thesis applies of generalized variational principle to present differential equation of self-anchored suspension bridge free vibration. Aimed at structural feature of usual three-span continual self-anchored suspension bridge, simplified differential equation, free vibration frequency formulas of longitude and vertical is achieved, and the thesis still presents formula of torsional vibration style and simplified differential equation of transverse vibration.(2) Considering geometric non-linearity and initial load, the thesis presents element stiffness matrix expression of stiffness girder and cable. When based on FEA to analyze seismic response of self-anchored suspension bridge, it studies on stiffness girder and cable element stiffness matrix's component. Taking into account structural characteristic that stiffness girder bears axial compression, it presents expression of girder element stiffness matrix. Neglecting large-displacement stiffness matrix, considering linear and geometric stiffness matrix, it presents expression of cable element stiffness matrix. The thesis still studies on conversion of cable element stiffness matrix under global coordinates. In the analysis of seismic response, aimed at structural element stiffness matrix's characteristic that the structure to be supported by cable is different to others, for geometric nonlinear factors which is brought forth by structural large-displacement, self-load's rise to span of cable and initial load etc., the thesis applies to Newton-Raphson's iterative method, Ernst's formula and addition geometric stiffness matrix which is brought forth by initial load to take into account, respectively.(3) Based on 2D-coherence function model and triangular series method, the thesis programs to produce artificial seismic wave, and under different seismic excitations to apply of great mass method, it analyzes nonlinear time-history response of self-anchored suspension bridge in detail. Based on 2D-coherence model, assumed static nonlinear balance to be as initial state of bridge structure seismic response analysis, after studying on PSD (power spectral density) function model of artificial seismic wave and incoherence function model, considering effect of vertical seismic wave promulgating direction to other supported points, selecting Hao's 2D-coherence model, applying of triangular series method and MATLAB the thesis achieves artificial seismic wave program and produces six points artificial seismic acceleration waves of the actual bridge. Considering geometric non-linearity, wave passage effect and incoherence effect, it studies on multi-support excitation. Applying of great mass method and artificial seismic wave, under strong shock, the paper analyzes seismic response character of towers and piers in detail. At last, considering material and geometric nonlinear, it analyzes self-anchored suspension bridge structural response under multi-dimension uniform and non-uniform excitation. Under static nonlinear balance state, it shows that the effect of geometric nonlinear is little to seismic response; the time that the moment occurs to crest value can be lagged and the girder mid-span displacement will increase as seismic wave promulgating velocity increase; comparing with uniform excitation, when taking into account wave passage effect, moment of tower and girder is larger than that of uniform excitation; considering every support point's coherence effect each other which their connecting lines are vertical with seismic wave promulgating direction, it will affect moment of tower bottom and girder tower's interface and displacement, but 2D coherence effect is not obvious, so 2D coherence effect may be neglected and only considered 1D coherence effect in the seismic response analysis; plastic material may disseminate energy, and it can affect structural crest value of seismic response.(4) Summarizing four dimensionless parameters which affect seismic response of self-anchored suspension bridge, studying on reference value of girder and ratio of rise to span parameters, presenting design curves and tables which corresponding tower girder parameter and tower parameter. Studying on effect of parameters, which include main-span, girder's width and height, tower's height, area of single tower bottom, ratio of rise to span and damping ratio etc. parameters. Through analyzing those parameters' affection current and relativity and furthermore optimum seeking to constitute, the thesis presents four dimensionless parameters, which are girder parameter k₁, tower girder parameter k₂, tower parameter k₃ and ratio of rise to span ratio k₄. Adequately considering variation range of bridge's dimension and different seismic excitation model, based on girder parameter and ration of rise to span parameter to be 0.037 and 0.125 respectively, through enough analyzing, calculating tower girder and tower parameters in detail, the thesis achieves curves and tables that are correlation with the above-mentioned two parameters, and the curves and tables may be used in structural plan design or initial design.(5) Studying on amended parameters correlation with girder and ration of rise to span, presenting simplified approach to analyze seismic response of self-anchored suspension bridge and checking its feasibility. Analyzing affection of girder and ration of rise to span parameters to seismic response, through two structural amended parameters, that is, girder width amended parameter k_B and ration of rise to span amended parameter k_λ, the thesis achieves correlation tables. Based on elastic concept and applied of stress and displacement to estimate seismic response, presenting simplified approach that applies of girder, tower girder, tower and ration of rise to span parameters to analyze seismic response of self-anchored suspension bridge. The approach may expediently calculate amplification factor of tower bottom that is specific value total stress to be produced by dead-load stress and seismic stress with dead-load stress, and amplification factor of tower and girder interface that is specific value total stress to be produced by dead-load stress and seismic stress with dead-load stress, and under seismic effect it may still calculate maximal vertical displacement of mid-span and maximal horizontal displacement on the tower top. Through five actual self-anchored suspension bridges to check, it may draw a conclusion that simplified approach is feasible to analyze seismic response of self-anchored suspension bridge.