Study On Parameter Sensitivity And Several Problems Of Self-anchored Cable-stayed Suspension Bridge

Self-anchored cable-stayed suspension bridge is a new type of bridge. It will become a competitive bridge type in the long-span bridge system because of strength rationality, construction safety, good adaptability to poor geological conditions and economy. At present, there are few relevant papers on self-anchored cable-stayed suspension bridge. But this bridge type has a particular advantage under specifically condition. It is necessary to carry out systematic study on this new bridge type. Combined western traffic construction scientific and technological project of Ministry of Communications and under the background of Dalian Gulf Bridge, this paper studies the simplified calculation method, sensitiveness of structure parameter, the influence of fracture of end hanger to the performance of self-anchored cable-stayed suspension bridge and strengthening the existing suspension bridges by changing suspension system into cable stayed suspension system. The main research work covers the following aspects:1. Based on energy principle, a named isolated body approximate method is proposed to calculate the behavior of self-anchored cable-stayed suspension bridge. The main cable, stayed cables and hangers of self-anchored cable-stayed suspension bridge are truncated and replaced by unknown forces in this method. The formulas for calculating the internal forces and deformation of girder and the internal forces of cable system are deduced. Take Construction bridge in Zhuanghe as an example, the calculation results of isolated body approximate method and finite element method is compared and the results of this two methods are matched well.·2. Under the background of Jinzhou Gulf Bridge, the influence of structure parameters to the behavior of self-anchored cable-stayed suspension bridge with steel-concrete mixed girder is researched. The result shows that:the influence of suspension-span ratio is significant. With suspension-span ratio increase the stiffness of structure is decreased and the max deformation and bending moment of the main span is increased greatly. The stiffness of structure can be increased by increasing rise-span ratio of suspension part, but the rise-span ratio has been degraded to be a local parameter. Though the deformation of the main span can be reduced by increasing the flexural stiffness of girder, the moment of girder will be greater. The stiffness of structure is increased greatly with the increase of tension stiffness of the main cable. The max deformation and bending moment of the main span deduce significantly while the tension force of it increase.3. Considering the uncertainties of the material and the physical dimension, the response surface approach is adopted to analyze vibration characteristics and critical wind speed of self-anchored cable-stayed suspension bridge. The nonlinear FEM model is established and the influences of random variables to vibration characteristics and critical wind speed of self-anchored cable-stayed suspension bridge is researched. The result presents that the dense of girder is most sensitive to the low-order frequencies of self-anchored cable-stayed suspension bridge while the dense and section area of girder impact the critical wind speed obviously. The conclusion mentioned above can help the designers to understand the influence extent of each random variable to the performance of self-anchored cable-stayed suspension bridge and supply theoretical foundation to design practice.4. It is one of the most important questions to cable-stayed suspension bridge that the end hanger is always under alternative stress which cause the hanger fatigue. Aiming at this fact, the research on influence law of end hanger fracture to mechanical properties of self-anchored cable-stayed suspension bridge is carried out based on damage theory of hanger. Static analysis of this type bridge under different fracture conditions is performed firstly. Then, considering time effect time-history analysis of mechanical properties under the end hanger fractured is conducted. The investigation indicates that under static effects internal force redistribution of the hangers adjacent of fractured hanger is significantly while the beam deflection, moment and tension of main cable of self-anchored cable-stayed suspension bridge are influenced little. By enhance the safety factor of end hanger and its adjacent hanger of self-anchored cable-stayed suspension bridge the structure will not fail foot by foot when end hanger is fractured.5. Based on transformation project of Shengdao bridge, a method of strengthening the existing suspension bridges by changing suspension system into cable-stayed suspension system is presented. The choice of strengthening manners, the changing of the structural system and the static behavior of the bridge before and after the strengthening is discussed. Besides that the characteristics and economic optimize of the cable-stayed suspension system is preformed also. The results indicate that it is feasible to strengthening the existing suspension bridges and greatly improve capacity of carrying load of it by this way. The mechanical behavior of original bridge is improved while the materials of the original bridge can be used to the greatest degree which makes economic advantage. Comparing the cable-stayed-suspension system by strengthening the existing suspension bridge to the traditional cable-stayed-suspension system, the two systems are formed in different order. The suspension system and stayed cable system bear their dead load independent and bear live load together.