Mathematical background for applying multiple axes random stress histories in the fatigue testing of offshore tubular joints

Abstract

Fatigue testing of large scale tubular joints has progressed to the point where a realistic in-service stress history can be used to obtain more representative fatigue data. In order to establish some standard histories to correlate data colleted by different laboratories and to characterize the in-service load histories for fixed offshore structures in the North Sea, an international committee on Wave Action Standardized History (WASH) was set up. After several years of collaboration, the first set of WASH recommendations has been finalized. These recommendations include the establishment of a standard stress-time history generation framework and three sets of input data for different configurations in the North Sea. While the WASH development is being continued for more complex stress histories, enhancement of the first standard framework has also been undertaken for application in multiple axes fatigue testing of tubular joints. This paper outlines the standard WASH generator and reports the enhancement required for generating and applying multiple axes of stress histories to fatigue testing. The spatial arrangement and mechanical interaction of the multiple actuators will be discussed and analysed. Sample histories are used to demonstrate the applications in tubular T joints.