| Spanning the Lancang River, the Lancang River Bridge with a main span of 342m, which is located in Dali-Ruili Railway with a design speed at 140km/h, is a deck arch bridge reinforced with concrete-filled steel tube. The stiff skeleton is a steel truss structure, which turns into a single cell and single box section of the main arch structure by filling and outsourcing concrete after swivel construction. The bridge has characteristics of long span and complexity in structure and construction techniques. According to the construction needs of this great bridge and requirements of Railway Ministry technology developing programs, this paper tentatively studies free vibration characteristics and seismic behavior of this bridge. The main research work and results are summarized as follows.1. On the basis of the construction characteristics and structure characteristics of the Lancang River arch bridge reinforced with concrete-filled steel tube, beam unit and plate unit are adopted, and the static and dynamic force analysis finite element module is set up via large finite element program. And then the precision of the built modules is compared and explored by the author. It comes to a conclusion that the influence of approach bridge should be considered in the earthquake proof analysis.2. With the assistance of multiple Rize vector, this paper analyses this bridge's free vibration characteristics and studies dynamic performance. The results indicate that this bridge has stronger stiffness than other congeneric bridges.3. Based on vibration mode superposition method, response spectrum method and time history analysis method are separately used to Lancang River Bridge's simultaneous incentive earthquake proof analysis. Then two different internal force and stress of the main arch's crucial section which are calculated by two different ways are compared in this paper. The allowable stress is adopted to evaluate vertical and transverse seismic behavior on the influence of three kinds of seismic force:the seismic frequent intensity, the seismic fortification intensity, seismic seldom intensity. The results tell us that outsourcing concrete and steel pipe stress is within the limit of allowable stress;the steel pipe stress of crown of arch exceeds allowable stress in the condition of rare earthquake transverse (both of consider live load or not), but it is less than ultimate strength. Calculation of ultimate bearing capacity of arch crown section indicates that, with an impact of rare earthquake, the internal force of arch crown section is less than ultimate bearing capacity; the safety factor surpasses 2, consequently, it can meet the design requirements of earthquake proof.4. As we all know, filling concrete contraction creep has an influence on redistribution of stress. To take the reduction of filling concrete modulus of elasticity into consideration, this paper discusses the changes of main arch crucial section's internal force and stress with different reducing coefficients. The results turn out to be that, the more reduction of filling concrete modulus of elasticity, the smaller of the section's internal force and stress. And what's more, the change is basically of linear relationship.5. Earthquake proof analysis with progressive wave effect considered is presented in this paper. The analysis result illustrate that the effect considered progressive wave is unfavorable to the internal force of main arch. In the analysis of bridge direction, internal force and stress decrease according to the accretion of seismic wave speed, eventually, approach the simultaneous incentive results. In the study of cross-bridge direction, the stress has a few changes; at the meantime, the impact of seismic progressive wave effect in the cross-bridge direction of this bridge is less than that in the bridge direction.From what has discussed above, we may safely draw the conclusion that seismic behavior of Lancang River Bridge can meet the design requirements under frequent earthquake, design and rare earthquake conditions. |
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