1982 年 1982 巻 152 号 p. 439-449
Among various offshore structures, semi-submersible rigs constructed of large diameter steel tubes have been given various types of reinforcement at their brace connections to insure their fatigue strength, which is one of the important problems directly related with the integrity of such structures
The rapid growth in development of marine resources has led to severer design conditions of a semi-submersible rig to be built for operation in deeper waters subject to higher waves and polar atmosphere. On the other hand, the pursuit of economy in the development is also an essential problem. This paper presents, as an approach to the above problems, a fatigue strength assessment method obtained through the development of a highly fatigue-resistant connection with considerations given to some problems involved therein.
For higher fatigue strength, one of the measures to be taken is to reduce stress concentration. With the new connection, it was possible to limit the stress concentration factor below 2 for welds at bracket toes, intersections, etc. From this fact, the fatigue life will be expected to sufficiently exceed the endurance period of 20 years.
Unexpectedly great influence on fatigue strength has been observed depending on the determination method of the stress frequency pattern and the wave direction, which are considered to be thoroughly clarified for future improvement of the design accuracy.
