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The fracture mechanics approach to design of steel structures uses the stress range distribution function as the main parameter that governs crack propagation and possible failures. It is an accepted fact that all welded structures contain existing small cracks that propagate as a function of varying stress ranges and stress intensity factors. The main problem is to predict correctly the nature of the varying stresses and to analyze them for fatigue evaluation.
Crane structures are exposed constantly to different static and dynamic loads and their stress distribution is quite complex. In this study, stress distributions in an overhead travelling bridge crane beam are evaluated by computer simulation and by monitoring real structures with a specially developed test setup.
The simulation starts with generating beta distributed random loads, and random loading and unloading places in the service area. These points are generated by means of a new general distribution model. Stress peaks and ranges are calculated and counted per each loading cycle.
The test setup uses regular load cells, with specially designed fixtures and A/D converters, to record data on perforated tapes.
The simulations were used to plot general distributions of stress peaks and ranges. The test results are special cases of the general distributions.
The results of this study are being used currently to evaluate fatigue lives and safe stresses in crane structures, and to update design codes.
peak stresses, crack propagation, fatigue damage, crane beams, service loads, stress history, fatigue tests
Adjunct professor of Mechanical Engineering, Technion, Israel Institute of Technology, Haifa,