| The vehicle-mounted emergency bridge is loaded and transported by the bridge truck.It canquickly complete the automatic erection in the emergency state,and strive for valuable time for road rushing.During the earthquake relief period,it will play a key role in the rescue and rescue of the people in the disaster area..However,in the recent years,China mainly uses artificially built temporary steel bridges in the disaster area,which has shortcomings such as long erection time and large manpower requirements.The research and design of internationally advanced mechanized bridges(such as vehicle-mounted emergency bridges)is still in its infancy,and only a very small number of companies have invested in certain technical forces for research,design and production.However,even these companies that carry out vehicle-mounted emergency bridge research and development are technically imitating foreign mature products for retrofitting,and the design methods are relatively backward.There is no modern technology design and calculation,and the “bigger” method is often used for structural design.The key indicators such as stress,deformation and life of the bridge are not well grasped,resulting in long design cycles,large material consumption,and unreasonable structure.In this regard,this paper takes an emergency bridge designed by a company as the object,uses the finite element method for strength analysis and structural optimization,reduces the weight by 15% based on the original design,realizes lightweight,and at the same time,fatigue of the bridge.The life calculation ensures the normal service life of the bridge.The main contents and results of this paper are as follows:(1)Based on the 3D model of 25 m emergency bridge,settingup the finite element modeling and finishing pre-processing work in Hypermesh,using the pumping midsurface method to simplify the bridge into a planar structure and then dividing the 2D mesh,select several specifics according to the actual situation.The working conditions are loaded to lay the foundation for subsequent analysis.(2)The static analysis is completed in the finite element software Abaqus,and the stress and displacement of the bridge under different working conditions are analyzed.It is found that the eccentric driving of the vehicle has a great influence on the stress concentration on the bridge surface;The buckling analysis finds the position of the first instability in the structure and calculates the instability adjacent load.The topology optimization method is used to optimize thestructure and obtain the bridge optimization scheme.The material can be reduced by the appropriate position on the web and the bottom of the bridge.Reduce the overall weight,achieve a weight loss of 15%,while ensuring the structural strength requirements.(3)Dynamic simulation analysis of the bridge structure,modal analysis,obtaining the first six-order mode map and natural frequency,judging the vibration condition of the bridge in combination with the driving situation of the vehicle,determining the range of the safe driving speed;calculating the fatigue life,According to the results of static analysis,the reference nodes are selected to analyze the stress time history to determine the dangerous position,and the rain flow counting method is used to calculate and simplify the stress time history of the dangerous nodes.The equivalent stress is calculated according to the Goodman equation,combined with the modified S-N curve of the parts.Miner's linear cumulative damage rule calculates the amount of fatigue damage at dangerous locations in each cycle,and estimates the fatigue life of the bridge to reach the secondary cycle.The results show that the vehicle trajectory and the position of the ribs have a certain impact on the fatigue damage,and the fatigue life of the bridge as a whole meets the actual use requirements. |
PDF Full Text Request