Vibration Characters Of Middle Length Span Rigid Beam Of High Speed Maglev Transportation

With the development of maglev transportation in china, maglev transportation lines will need crossing the river and main road in city. By the technology introduced from Germany or developed by our country, the guideway in existence nowadays only can cross small distance (not more than 25m) [0]and can't meet the requirement of crossing long distance. [0]It is necessary to study and develop new style moderate span bridge (span 40m~100m). Meanwhile because the three span rigid bridge has a good structural stiffness and steady vehicle traveling, it has some special advantages. Technology introduced from Germany only give two style bridge designing models: simple span bridge and double span bridge. It has a rigid requirement of dynamic performance. According to this requirement , the bridge must have a large rigidity and the cost is high. It is also difficult to construct. So in this thesis, the static and dynamic performance of three span rigid bridge is analyzed.Character of bridge's free vibration is one of the most important dynamic performances. In this thesis, the mass and rigidity of the three span rigid bridge is considered as continuous. And the analysis model for free vibration of the bridge is set up. Compared with the finite element model, the continual structure model is more near to the reality and better to reveal the free vibration rules. In this thesis, the relationship between deflection and frequency with span ratio and pier stiffness are analyzed. And it draw a conclusion that the value of span ratio from 0.5 to 0.7 is fit, ratio of pier stiffness and bridge stiffness fixed as 2.4 is also fit .Under the instruction of above conclusion, and also considering the requirement of free vibration frequency and static loading required stiffness, 12 kinds of status of 3 different span ratios and 4 different stiffness is set up.Vehicle–bridge coupling analysis model of two stage suspension is set up and a simulation calculation program is done. The bridge's vibration with speed from 100km/h to 600km/h is analyzed by using calculation program. The relationship between the bridge vibration with vehicle speed, span ratio, stiffness, damp ratio, mass, frequency is analyzed. It indicates that the bridge vibrates more severely with higher speed. In the analyzed range of span ratio from 0.5 to 0.7, the bridge vibrates more severely with bigger span ratio; so it is better to choose smaller span ratio. Impact factor becomes smaller with the improvement of bridge's section stiffness. So improvement of stiffness can weakens vibration directly. And when the section is smaller, impact factor becomes smaller with the improvement of bridge's section stiffness more directly; when the section is bigger, the trend of impact factor becoming smaller with the improvement of bridge's section stiffness becomes flat.In this thesis, reasonableness of first step frequency requirement f1≥1.1v/L is discussed. Resonance will not happen when f1 is equal to 1.1v/L. And requirement f1≥1.1v/L is considered to be too conservative. Under technology in existence, the method used in this study is suggested. First, set the upper limit and lower limit of section stiffness requirement. And then according to vibration impact of bridge among the stiffness range to set the stiffness which is not alert to change of impact factor. At last choose reasonable section.