Dynamics Of Beams Of Truss Structure Bridge Inspection Vehicle

Truss structure bridge inspection vehicle is a special vehicle that can provide work pass and plat for bridge maintenance, playing an important role in bridge engineering. The beams of truss structure bridge inspection vehicle deploy and extend to the bottom of bridge during work. Then the work staff and equipment go into the work plat through the pass. Therefore, the safety and reliability of the beams directly relative to the safety of the staff and equipment. The inspection range of the truss structure bridge inspection is expected to be larger with the construction of bridges with larger span, length and depth. The beams deploy to form a longspan, suspended structure, to be susceptible to environmental stimulations. Besides, the telescopic mechanism, vertical beam and loads need to start and stop or move frequently to adjust work position. Additionally, the beams are vulnerable to vibration due to severe work condition, reducing work comfort of the staff and safety of the beams. According to the industrial standard currently carried out, ‘QC/T286-2010’, the velocity of the beam motion is slow, which makes the operation inefficient. Hence, the operation speed should be improved to reduce operation time as well as impacts on the traffic. However, this makes the beams more susceptible to shocks and loads, further reducing the stability and increase the risk of accidents. Therefore, to reduce vibration of the beams, improve operation efficiency, enhance dynamic capacity and finally improve the safety and reliability, urgently attention should be paid to the dynamic characteristics of the beams for truss structure bridge inspection vehicle.First, dynamic characteristics of telescopic mechanism during free telescopic motion are investigated. The overlap part in the telescopic beam is equivalent to time-dependent mass at the end of the constant beam. The equations of motion for the telescopic mechanism are derived using the Hamilton’s principle, transformed into discretized equations and solved by employing the Galerkin’s method. The eigenfunctions of the two-stage and multi-stage axially telescopic beams are derived based on the time-dependent kinetic and dynamic boundary conditions. The partial derivatives of the eigenfunctions to time are acquired by taking the impact of the change in length of the telescopic mechanism on the dynamic model. Influence of the time-dependent eigenfunctions to the dynamic characteristics of the telescopic mechanism is revealed.Then, dynamic responses of the telescopic mechanism during forced telescopic motion are investigated. Dynamic model of the telescopic mechanism under moving mass is established based on the equations of motion for free telescopic motion. The influence of different mass and telescopic mechanism strategies on the dynamics are studied. Considering the gravity center shift, impulses at the step transformation and human-structure interaction, dynamic model of the telescopic mechanism under pedestrian is established by employing inverted pendulum model. Additionally, dynamic model of the telescopic mechanism under beginning excitation is established. The deformation of telescopic mechanism in this condition is derived and influence of the beginning excitation on the dynamic responses is presented.Third, dynamic characteristics of the beams during vertical beam lift are investigated. Dynamic model when vertical beam lifts separately is established. The eigenfunctions are acquired based on the boundary conditions of the vertical beam, constant beam and telescopic beam and the partial derivatives are derived. Influence of the lift for vertical beam on the dynamics of the beams is obtained. Dynamic model when telescopic mechanism and vertical beam move axially and synchronously is established. The influence of motion strategy for telescopic mechanism and vertical beam on the vibration are presented to explore motion strategy that can avoid large vibration and improve work efficiency. The dynamic model is verified by way of experiment.Last, dynamic characteristics of the beams during telescopic mechanism roatation are investigated. The rotating telescopic mechanism is described from the kinematics based on the principle of gyroscope with the lateral deflection and axial flip of the telescopic mechanism considered. Lateral-transverse-torsional coupling dynamic model is establised in this condition. Influence of the angles for lateral deflection and axial flip, rotation velocity and acceleration on the dynamics are analysed. The dynamic model is verified by way of experiment. Considering the influence of telescopic mechanism rotation on the unbalance load of the vertical beam and dynamic load from the vibration, measurement of the extension for the vertical beam cylinder in real time is presented. Improvement strategy of the hydraulic system to avoid dynamic and static buckling instability is developed.