Abstract. In the course of manufacturing and operation, there can appear cracks in loadcarrying metal structures which are hard to be detected till a definite moment. That is why in the course of designing metal structures, it is necessary to ensure their durability during possible existence of cracks up to the next routine inspection of a structure. For the prognostication of the durability of a structure with a crack, a research of coefficients of stress intensity on end-element models with crack-like defects of different length is carried out. As a result of this, a procedure for the definition of crack-resistance resource allowing the supposition of safe operation of a metal structure with a crack within the limits of recurrent routine works is developed. IntroductionBoth technological and fatigue cracks can appear in parts of load carrying metal structures in hoisting machines during production or operation processes. The resistance of metal to structure crack propagation is called fracture toughness.The known concept of secure damage is based on the assumption that in any metal structure, even in new, there are always defects that may remain long undetected. Dimensions of detected defects are determined by resolution of applicable testing aids. All defects which are beyond the scope of testing aids remain undetected and, when present in the metal structure, they are potentially dangerous for metal structure operation.To assess the vitality and the remaining life of metal structures, as well as to assess the impact of technological and operational defects on their load-bearing capacity, we must have a calculation device to predict behavior of metal structures with cracks under operational loads, which includes methods of fracture mechanics using the stress intensity factor (SIF) as the main characteristics of the stress and strain state of the material near the crack tip. The value of SIF may be found, for example, by reference data [1,2] or by numerical methods. However, SIF guides do not contain practically any solutions to the cracks in the spatial objects of box-section typical for parts of metal structures of hoisting machines. In the paper presented this problem is solved on the basis of the end-element modeling of structures with crack defects with the purpose of the assessment of metal structure durability at the stage of designing.

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