Study On Seismic Behavior And Dynamical Stability Of Large Span CFST Arch Bridge

Concrete filled steel-tube (CFST) arch bridge has been widely applied in our country for its good mechanical properties and facilitated in construction et al. Taking 308m span Nanpu Bridge as the object of study, the nonlinear seismic response behavior, the seismic response characteristic under multi-dimensional and multi-support excitation and the dynamical stability properties of long-span CFST arch bridge were investigated in depth. The motion stability practical criterion of arch structure is brought forward on the base of Lyapunov theorem of motion stability.The semi-analytical solution of elastic circular arch under horizontal random stationary and non-stationary seismic excitation was studied by the method combining the pseudo-excitation algorithm with Galerkin algorithm. A numerical example was given to demonstrate the accuracy and efficiency by comparing the results with finite element method.The nonlinear time-history analysis of long-span CFST arch bridge under three-dimensional earthquake excitations was performed. The influence of geometrical non-linearity, material non-linearity, damping ratio and bridge deck was studied by seismic response analysis. The results show that the lateral bending moment and axial force around the springing of arch rib increase greatly taking account of bridge deck. Geometrical non-linearity has some effect on seismic response of CFST arch bridge. The displacement of arch rib and the axial force of most section increase because of the reduction of stiffness. Material non-linearity put the sections of springing of arch rib nearby at a disadvantage.The random seismic response analysis of Nanpu Bridge under multi-support excitations of three-dimensional orthogonal earthquake motion was performed. The seismic response of the arch bridge under one-dimensional P-wave, one-dimensional SH-wave, one-dimensional SV-wave and three-dimensional considering cross-power spectrum of multi-support earthquake excitations were numerically simulated. The results show that the internal forces of arch rib may be greatly changed by considering the spatial variation of seismic motion. The influence of spatial variation of seismic motion on the internal forces of arch rib primarily comes from travel ing-wave. The internal forces of arch rib under three-dimensional earthquake excitations are greater than that under one-dimensional excitation. The random seismic analysis under three-dimensional and multi-support earthquake excitations must be performed for the long-span CFST arch bridge otherwise the seismic design forces of the structure are likely to underestimate seriously.The practical stability criterion of structure motion and the specific steps were proposed. The instable characteristics of arch structure were investigated under step load, cyclic load and earthquake excitation. It is indicated that negative eigenvalue appearing in structure whole stiffness matrix is requirements for structure instability and the lower limit of critical load of structure dynamical instability is estimated. The displacement time-history curve becoming divergent, a change of qualities, a leap taking place or the motion chaos can be basis for structure dynamical instability.The static and dynamic plastical stability analysis of long-span half-through trussed CFST arch bridge were studied. The result indicates that the material non-linearity decreases static stability coefficient of long span arch bridge greatly. The Budiansky-Roth criterion is invalidate in the analysis of elastic dynamic stability of long span arch bridge and the critical load of dynamic stability can be estimated by negative eigenvalue appearing in structure whole stiffness matrix. Lateral earthquake excitation is the most disadvantageous direction in dynamic buckling analysis. Initial geometric imperfection makes no difference on dynamic stability of arch bridge but yet affect static stability of arch bridge deeply. The plastic dynamic buckling mode of arch bridge is partial buckling of arch rib and seismic wave disturbance has little influence on static stability coefficient of arch bridge.