Electric single girder crane girder Common Problems

Electric single girder  eot crane  is widely used in various fields of national economy and sectors, is a modern large-scale industrial production of indispensable equipment. Since the use of electric single girder crane special circumstances in the course of the event of collapse accident will cause plane crash. Author based on several years of testing experience electric single-girder cranes several common issues are analyzed and discussed.

Electric single girder overhead bridge crane  girder severe premature cracking analysis

The base material of the main beam web or weld material yield due to the lower limit of alternating stress under repeated, after a certain number of cycles later, the stress concentration portion of cracks and under certain conditions continue to expand until a final sudden rupture. Actual material fatigue life that is experienced before fatigue stress cycles below the theoretical calculation of cycles greater than one million times, according to the conventional theory of fatigue calculation method. Assuming no initial crack, fatigue test specimens shall be obtained by material fatigue limit of the material or the basis of the curve due to the surface and then consider the shape, size and geometry of the stress concentration caused by other factors. Fatigue test data as discrete large specimen fatigue life and stress level is not one to one relationship between a single value, but with the survival time of the test specimen closely. The higher survival rate in the same fatigue life situations the lower the fatigue strength. According to China's crane design specification requirements of steel because of the importance of the fatigue strength survival rate of 90% shall be S-N curve selection. Electric single-girder crane design stress cycles N is greater than the fatigue limit of the material yield curve corresponding to the number of cycles NS ≈ 105, but less than the stress cycle cardinality NO ≈ 107. N corresponds to the fatigue strength under the main beam finite life fatigue calculation, taking into account stress cycle characteristics and effective stress concentration factor.

Electric single girder bridge crane  is designed to work level A3, A4, A5, theoretical design life of 20 years. Metal Slitting its main girder crane factory weld cracking are open prematurely serious local stress concentration, did not take that stress dispersion strengthening local measures. Studies show that there is higher than the fatigue limit load exists, below the fatigue limit stress, such as weight load stress can also cause fatigue damage, you must apply the cumulative damage theory, considering the damage below the fatigue limit but above the limit of stress injury.