Journal of Engineering for the Maritime Environment, Feb 2015.
Shanshan Li1, Weicheng Cui2, Jeom Kee Paik1
1. The Korea Ship and Offshore Research Institute (The Lloyd’s Register Foundation Research Centre of Excellence), Pusan National University, Busan, South Korea and
2. Hadal Science and Technology Research Centre (Shanghai Engineering Research Center of Hadal Science and Technology), Shanghai Ocean University, Shanghai, China
The load sequence effect has been proved from laboratory tests to be an influencing factor that cannot be neglected in the fatigue analysis of marine structures. To take account of this significant factor, fatigue life prediction should be based on fatigue crack propagation theory rather than the currently used cumulative fatigue damage theory. Accordingly, fatigue loading needs to be provided as the load-time history in the time domain rather than the load spectrum in the frequency domain. A general procedure for generating the standardised load-time history for marine structures based on a short-term load measurement has been proposed by the authors. This article seeks to further improve on this procedure and explain how to apply the determined standardised load-time history in the fatigue life prediction method based on the fatigue crack propagation theory. Finally, generation and application of a standardised load-time history are given for a tubular T-joint of an offshore platform, which demonstrates the practical and effective use of the proposed approach.
Fatigue is considered to be a main failure mode for marine structures such as ships and offshore platforms. Both for economic design and for safe operation, it is very important to accurately predict the fatigue crack growth process under service loading for marine structures. In order to apply the fatigue crack propagation (FCP) theory to a newly designed marine structure, one needs to provide a time-dependent fatigue load history that represents the fatigue loading series encountered. In the present paper, an improved general procedure for generating a standardised load-time history (SLH) for any marine structures based on short-term load measurements is proposed. Additionally, how to apply the determined SLH in the unified fatigue life prediction method is explained in detail. Finally, an example is given to demonstrate the generation and application of the SLH for a tubular T-joint of an offshore platform. The method can be easily implemented into any commercial software for structural analysis and design.