Inversion Of Vehicle Vibration Load For Chongqing Straddle Monorail Transit

With the rapid development of urbanization, urban rail transit, as a kind of way to solve urbanization problems such as traffic congestion, environment pollution, plays an important role, which is becoming increasingly clear. Straddle monorail transit system, as a special rail transit form, with the characteristics such as low vibration, poor influence on urban landscape and daylight, good ability of slope climbing, and so on, is better and better received by the planners in the construction of rail transit. At the same time, the study of problems of straddle monorail transit system such as vibration of structures, the computation of vehicle load and so on, is on the agenda.Based on the engineering background of Chongqing straddle monorail transit system, dynamic load inverse theory in the problem of structure vibration is summarized and developed; the simulation theory and the calculation method for the vehicle load of the straddle monorail is discussed. Besides introduction and conclusion, this paper consists of following content:First, as the calculation method of direct problem in structure vibration, the computation theory of dynamic finite element method was summarized. The formation of the dynamic equilibrium equation, the Newmark implicit integration method for solving the equilibrium equation, and the artificial dynamic boundaries are described in detail.Second, based on the dynamic response computation formula of single degree of freedom system, through the expression of dynamic load into discrete Fourier series in time domain, the dynamic response of single degree of freedom with the form of discrete Fourier series is given. On the base, with the transformation and deduction in discrete Fourier transform method and discrete Fourier series method respectively, the formula is deduced to a method of calculating the amplitude coefficient of steady vibration in discrete frequencies. A numerical case is given to test the feasibility and rationality of the method.Third, for the deviation of baseline from equilibrium position in the displacement time-history integrated from the tested velocity time-history, some correction method for this type of problem is discussed. With one of the methods adopted, the tested velocity time-history and its integrated results are corrected.Fourth, dynamic load inverse formula of single degree of freedom is derived from the amplitude coefficient solving method of steady state vibration. Considering the mode superposition method, the vibration load inverse formula in multi-degree of freedom system is deduced.Fifth, finite element modal of elevated bridge pier is built. The simplified modal of vehicle load in straddle monorail system, the simulation theory and computation method of vehicle load are discussed.Sixth, with the finite element modal of elevated bridge pier, the vertical dynamic load time-history at the simplified support bearing point in the top face of the capping beam is calculated with dynamic load inverse method. The dynamic response at the load point with this vertical dynamic load is computed with vibration theory. And the vehicle load is calculated with the rail acceleration which equals to the acceleration at the same point.