Experimental and Simulation Studies on Deflection–to–Span Ratio Limit of the 25m Simply–Supported Girder for Urban Maglev Transit.

Four commercial urban maglev lines have already been put into operation, demonstrating the safety, comfort, environmental sustainability, and low maintenance of this innovative rail transit system. To further promote and apply this technology, reducing line construction costs has now become a priority. The deflection-to-span ratio limit of the girder plays a significant role in determining the construction cost of commercial lines. According to Chinese standards, the vertical deflection-to-span ratio limit for simply supported girders under maglev train loads is set at 1/3800 to prevent strong coupling vibrations between the maglev train and the girder, which could lead to levitation failure (i.e. the collision between the electromagnet and the rail). However, the current deflection-to-span ratio used in commercial lines is smaller, contributing to the high construction costs of commercial lines. To investigate whether the deflection-to-span ratio can be reduced, a 25 m span variable-stiffness steel girder was designed and manufactured, with the deflection-to-span ratio range between 1/2000 and 1/4500. A coupled dynamic model of the maglev train-controllable electromagnetic force-variable stiffness girder was then established. Tests were conducted to analyze the dynamic responses of a single-car maglev train traveling over the variable stiffness girder at speeds of 20–60 km/h, with the results being used to validate the numerical model. The coupled dynamic simulation analysis was also performed for the three-car maglev train traveling at speeds ranging from 20 km/h to 100 km/h. By focusing on levitation gap fluctuations and ride quality, the study discussed an optimal deflection-to-span ratio for the 25 m span girder. Simulation results indicate that, regardless of the deflection-to-span ratio of the girder, the vertical accelerations of both the levitation bogie and the F-shaped rail initially decrease with increasing speed, then gradually increase. However, the vertical accelerations of both the carbody and the girder increase consistently with speed. As the deflection-to-span ratio decreases, the dynamic response of the coupling system gradually decreases. The deflection-to-span ratio of 1/2970 is optimal, ensuring both the safe and smooth operation of the maglev train while significantly reducing construction costs. [ABSTRACT FROM AUTHOR]