Derivation of Fatigue Loading

(1)P Loading for fatigue shall normally be described in terms of a design load spectrum, which defines a range of intensities of a specific live load event and the number of times that each intensity level is applied during the structure's design life. If two or more independent live load events are likely to occur then it will be necessary to specify the phasing between them.

(2)P Realistic assessment of the fatigue loading is crucial to the calculation of the life of the structure. Where no published data for live loading exist, resort shall be made to obtaining data from existing structures subjected to similar effects.

(3)P By recording continuous strain or deflection measurements over a suitable sampling period, loading data may be inferred by subsequent analysis of the response. Particular care shall be taken to assess dynamic magnification effects where loading frequencies are close to one of the natural frequencies of the structure. Further guidance is given in Annex C.l.

(4)P The design load spectrum shall be selected on the basis that it is an upper bound estimate of the accumulated service conditions over the full design life of the structure. Account shall be taken of all likely operational and environmental effects arising from the foreseeable usage of the structure during that period.

(5)P The confidence limit to be used for the intensity of the design load spectrum shall be based on the mean predicted value plus kF standard deviations, where kF = 2. The confidence limit to be used for the number of cycles in the design load spectrum shall be based on the mean predicted value plus kN standard deviations, where kF = 2. See also 3.4(2). The confidence limit to be used for the number of cycles in the design load spectrum shall be based on the mean predicted value plus kN standard deviations, where kN = 2. See also 3.4(2).

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