Determination Of Reasonable Finished State And Study On Some Problems For Self-anchored Cable-stayed Suspension Bridge

As a new type of bridge structure, self-anchored cable-stayed suspension bridge has not only many advantages as new structure, reasonable load, well wind resistant, safety of construction and low cost, but also has the merits just like that of traditional cable-supported bridge has. Owing to huge anchorage being canceled, this type of bridge structure becomes outstanding superior in soft soil base and strong wind areas, and also highly competitive in large-span bridge construction, especially in the cross-sea bridge construction. At present, there is little related research on self-anchored cable-stayed suspension bridge home and abroad. While because this type of bridge structure has its unique advantages in some special conditions, it is necessary to develop systematic research on it. Combining the scientific research project-the study on cable-stayed suspension bridges, which is the transportation construction scientific item for western regions held by the Ministry of Communications, with the engineering background of Dalian Gulf Bridge to be built, this paper focuses on calculating method for the reasonable finished dead state of the self-anchored cable-stayed suspension bridge and damping optimization design. Moreover, nonlinear stochastic static response and nonlinear dynamic response are both investigated systematically in the paper. The research work mainly covers the following aspects:1. Self-anchored cable-stayed suspension bridge structure is different from other bridge structures, which combines both stress characteristics and structural characteristics of cable-stayed bridge and self-anchored suspension bridge. According to the present available calculating methods for reasonable finished dead state of cable-stayed bridges and suspension bridges, the reasonable result couldn't be got. Under this condition, unreformed pretension principle of how to keep the internal Force of the cable remaining unchanged is deduced in this paper. Based on this principle and geometric nonlinear calculation, the step-by-step calculating method for the reasonable finished dead state of the self-anchored cable-stayed suspension bridge is proposed on the basis of some available methods. Utilizing related finite element calculating program and the self-developed MCFS program, the step-by-step calculating method could be conveniently carried out. It is shown from the practical calculation examples that the stiffening girder under finished dead state drawn through the step-by-step calculating method lies on the design curve and the dead load bending moment is well distributed. Moreover, the bending Moment of main tower is relatively small, horizontal displacement of pylon top is coming to zero and the cable force is even distributed. During calculation, the main cable and the stay cable as well as the sling are all simulated by using elastic catenaries cable elements. The results drawn from the calculation about undeformed pretension or unstressed cable length can be directly used in analyzing construction phases. 2. Considered the randomness in material properties, physical dimensions and other parameters of structural elements, the response surface approach is utilized to analyze mid-span deflection in stiffening girder and the whole stability of self-anchored cable-stayed suspension bridge structure. Taken mid-span deflection in stiffening girder as the research object, the nonlinear finite element calculation model is utilized in the stochastic static analysis. The variation of random variables for the mid-span deflection in stiffening girder and the whole stability of self-anchored cable-stayed suspension bridge structure is also analyzed. The result shows that the parameters of main cable have a great effect on the whole rigidity of self-anchored cable-stayed suspension bridge structure. The parameters of the concrete stiffening girder significantly influence the stability of the bridge structure. The above research results will help designers clearly know how different kinds of random parameters affect the response of self-anchored cable-stayed suspension bridge structure and provide reasonable theoretical evidence for bridge designing.3. Through the space finite element dynamic analysis for Dalian Gulf Bridge, the dynamic characteristic of self-anchored cable-stayed suspension bridge structure is analyzed. The modified response spectrum is utilized to analyze the structural seismic response in longitudinal, vertical, horizontal and under the effect of the two from the above three. Based on the memoir wave commonly used and the seismic wave artificial generated, the nonlinear dynamic time-history is analyzed. The average of the result is taken as the analysis result for the whole nonlinear dynamic time-history analysis. Compared this analysis result with the result from response spectrum analysis, it is obviously shown that the nonlinear dynamic time-history analysis is of great importance for this kind of bridge structure with huge span. The conclusion drawn from the analysis can provide reference for seismic design of the similar bridge structure and the analysis result shows that shock absorption design and isolation design are both necessary.4. Considered both geometric nonlinearity and boundary nonlinearity, the nonlinear dynamic time-history is analyzed by using Maxwell model to simulate damper. Proceeded from parameter variation of damper and option of installation position, the structural response under the effect of seismic load is specifically studied.The result from the study shows that energy dissipation of damper will be enhanced with the increase of damping coefficient C when velocity indexes a keeps certain and the displacement of damper, beam end and tower top will decrease monotonously. But in the area where the damper parameter is higher, the displacements for the lower velocity index are very similar and change mildly. While the variation for bending moment of pylon bottom remains slight only when damping coefficient comes to a certain value. The bending moments corresponding to velocity index are so similar in certain extend that they may affect the curves cross over each other. This suggests that, for bending moment, it doesn't mean that the smaller the velocity index, the better the damping effect. Damper has little effect on shear of Pylon bottom, but it is shown from the change of shear that there is a declining period. When damping coefficient is smaller, shear of pylon bottom will decrease with the increase of damper coefficient. While except the declining period, shear of Pylon bottom will increase along with the damper coefficient. According to this change, the reasonable and efficient shock absorption design scheme is studied. Based on shock absorption design scheme, the longitudinal displacement of gird and pylon under earthquake action can be reduced nearly 60% on the premise of no change static structural performance. The longitudinal bending Moment of Pylon bottom also can be reduced nearly 50%. All of this proves that shock absorption design scheme has significant effect on damping and it can efficiently minimize the harm caused by earthquake on bridge structure.