Global and local fatigue concepts

For the fatigue assessment of steel structures SKI Ingenieurgesellschaft uses the following fatigue concepts:

An overview of the fatigue Concepts offers the following representation: 

Fatigue concepts (schema based on Radaj)
Cracking on a specimen after dynamic loading

Evaluation of cracked components

The today's substructure are highly dynamic stressed structures, which must ensure on the one hand a sufficient stability and on the other the fatigue lifetime.

Cracking can occur in both concrete and steel structures. Damage often occurs at notched transitions or at stiffness joints with different materials. Examples are the base of a tower at the transition to the foundationRing flange connections of steel sections, transitions between concrete and steel sections in hybrid towers or the tower top connection to the nacelle. 

Due to the loads can cracks appear in concrete components which do not directly affect the load-bearing capacity of the structure. In this case, the reinforcement can absorb the tensile forces. This can be caused by an extreme load event in which high loads act on the construction and as a result cracks form. An increase in the crack width after this event does not necessarily have to occur or be critical. SKI uses various fatigue concepts based on fracture mechanics, including the Crack growth concept.

Classification of verification format

If cracks can be detected in the structure, it is important to assess whether the crack width increases with increasing operating time (crack propagation) due to the relatively high number of load cycles. The cracks may have a negative effect on the remaining lifetime of the structure. In this case, it may be necessary to develop suitable repair measures.

The SKI engineering company has welding engineers with national and international test certificates as well as publicly appointed and sworn experts for supporting structures of on- and offshore wind turbines.

In this context, SKI can provide technical assessments / appraisals for a wide range of cracked components:

Our services

For dynamically loaded components with a calculated fatigue assessment is to provide for the anticipated operating loads (fatigue analysis). For steel structures, the fatigue analysis is aimed to DIN EN 1993-1-9. Depending on the calculation method used for the internal forces, the calculated fatigue detection at the level of:

be performed in conjunction with appropriate damage accumulation hypothesis . For assessing the security against material fatigue are among experimental methods listed above concepts.

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