Research On Damage And Life Of Crane Girder Under Rising Load

Hoisting Machinery plays a positive role in promoting national economic construction. During operation, the agencies are often in a state of complex movements such as starting and braking, positive or rhetorical question motion, accompanied by the strong vibration and impact. Due to unstable amplitude stress, structures (institutions) will be damaged in different degrees, which directly affect the overall performance gantry cranes. As a key component of the crane, the damage and life of girder largely determines the crane's life. With the progress and development of manufacturing technology of hoisting equipment, the lifting capacity and transport distance of gantry crane becomes larger which produce a thorny issue that the safety factor of the girder requirements are also increasing. This thesis takes the impact damage and the fatigue life of the girder under the action of the lifting load as the research object, aiming at improving the comprehensive properties of the girder, providing the method for the structure design and optimization of the girder of gantry crane and providing a certain theoretical basis for the safe operation and the improvement of the economic benefit of the gantry crane, which have widely engineering application background and a certain academic research value.To reduce the cost of the simulation, this thesis establishes the simplified virtual prototype model of the girder. The mechanical properties and fatigue damage of the girder are analyzed by finite element software ANSYS Workbench and fatigue analysis software nsoft. The simulation results show that the maximum equivalent stress positions appear in the girder's web, the welded part of the upper cover plate and the web, the diaphragm and the connecting part of the web and the joints of girder and legs where easy to produce fatigue damage. Due to the compressive stress reduction the rigidity of structure by reducing the frequency, the prestressed modal frequency is slightly smaller than without prestressed modal frequency. The reducing of lifting weights will reduce the frequency of elevated. In order to ensure the efficiency of the crane and reduce the damage of metal structures, it is more appropriate that the start time of lifting mechanism is seted to 1-1.5s. Some very large value cyclic will produce fatigue damage, and most of the damage is produced by the generated and limited cyclic. The lifting capacity that more than 40t will significantly causing the damage of the girder. A conservative estimate of the girder under impact loading without repairing can be used for 24.7 years. Overload, residual stress, surface roughness and notch effects have a significant impact on the life of the girder. A mathematical model to calculate the fatigue life was used based on Paris formula and Minerlinear damage theory. The fatigue life of gantry crane girder is 24.59 years which calculated by writing MATLAB program. As can be seen by comparing the results of impact damage with fatigue life that the results are close which illustrates that the results of impact damage have certain credibility.