No abstract

It is well established that the fatigue performance of materials and structures may be very sensitive to the specifics of the loading encountered. Beside constant amplitude testing, therefore, tests with realistic load sequences are often requiered in order to to assess any susceptibility to the specifics of variable amplitude loading and to demonstrate the in-service integrity for given materials and sructures .For these purpose standardised load-times histories (SLH`s) have been developed for 30 years since it has been recognised that the use of SLH`s a series of adventages - both for studies of a more generic nature and practical applications. Starting with Gassner`s block programm test, some features of standardised load-time histories availible at present and their relevance for fatigue behaviour of materials and structures are reviewed

WASH 1 is composed of a defined series of six seastates for a yearly return period; the two lowest seastates 1 and 2 being eliminated, because they do not influence the fatigue life of offshore structures, and the three highest seastates 8, 9 and 10 were combined. The sequence and the duration of the resultant six seastates correspond also to long term observations in the North Sea. A generated load history with the power spectrum of the strain measuremnts used as a basis, is the result for each seastate. The return period of the standardized load history WASH 1 decided upon is 5 x lo5 cycles coresponding to one year of wave loads. It is fixed sequence of peaks recorded on tape. Testing frequency and signal shape are optional. The basis for the derivation of standardized load histories is always formed by strain histories measured in operation. WASH 1 was derived on the basis of strain measurements on the FRIGG DP2 platform of IFREMER, Brest, supplemented by measurements of Germanischer Lloyd, Hamburg, on the Research Platform NORDSEE. As even comprehensive measurements can only be samples over a limited period of time, the strain measuremments were supported by the results of long-term observations of seastates in the North Sea.

Structures and their components are often loaded multiaxially and stochastically under operational conditions. Load assessments must be done for both the theoretical fatique life estimation and/or for experimental fatique life determination of components in the laboratory; moreover for experimental laboratory testing the load assessments must be realized in an effective way. The Simultaneous Procedure offers the methods to solve both problems in the best possible way