Study On Fatigue Performance Of Welded Steel Crane Girder Before And After Being Reinforced

With the development of industry and the aging of industrial workshop, the phenomenon that the heavy steel crane beam has appeared fatigue crack of under repeated loads in different degrees is found. The upper part of the crane girders on the fatigue fracture mechanism, the domestic and foreign scholars do a lot of discussion and study, but have not get the satisfied results. No obvious macroscopic deformation and signs of fatigue failure, it often results in a sudden disaster and causes huge economic losses and casualties. Therefore, this paper proposes a reinforcement program, and does the fatigue test on crane beams reinforced before and after. It analysises the fatigue damage mechanism of the crane beam and the feasibility of the reinforcement scheme.This paper reinforces the top flange and web of the steel crane beam by angle steel and high strength bolts firstly. Then contrasts and analysis on the principal stress and direction of the steel crane beam with cracks and the web which is reinforced before and after. The results show that before reinforcement, the outside principal shear stress of the eccentric is two times bigger than the plane principal shear stress. So, the crack form is mainly on tear type (Ⅲ) cracks; At the outside of the eccentric, one million times before, the stress of the crack tip is mainly to the principal tensile stress, the direction of the principal tensile stress almost perpendicular to the crack propagation direction, so the crack form is mainly on open-type (Ⅰ) cracks;1million times later, the stress is mainly to the principal compressive stress, the plane principal shear stress is greater than the outside principal shear stress, and the direction generally parallel to the propagation direction of the crack, cracks form is mainly on slide open type (Ⅱ) cracks. After reinforcement, webs on both sides of the crack tip were not appearing the principal tensile stress which is beneficial to the crack propagation; stress is mainly on compressive stress, and much smaller than the reinforcement before. After reinforcement, the overall stiffness of the upper flange and web greatly increases, the main compressive stress of the eccentric side increases of2%-25%more than the eccentric lateral, the impact of eccentric greatly reduces. Eccentric torsional deformation of the upper flange greatly reduces and the stress amplitude is greatly reduced, it concludes that the reinforcement scheme is feasible and effective."The design of building structures unified standard" gives the limit state design method which is based on reliability theory; the fatigue limit state design is still using the allowable stress method. Therefore, developing the S-N curve of the fatigue loading and structural resistance, drawing the target reliability index of the structure in the state of fatigue and fatigue design expression based on reliability theory has become the main content of future research. This article references literature19that analysis the past crane beam fatigue test data, and calibrations the fatigue reliability of8categories connected and constructed forms in steel specification, and gives recommended values of the fatigue target reliability index. Finally though the formula it draws the remaining fatigue life of the crane beam.