A Study on Structural Standardization of Connections of Floating Offshore Structure

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Based on results of survey of structural reinforcements at connections of actual semisub- mersibles, two cases were inverstigated in this study; a case wher a brace is directly welded to outer surface of column and a case where a brace penetrates a column shell wall.On the other hand, based on results of analyses of actual semisubmersibles subjected to design waves, 12 kinds of foundamental load patterns were proposed to express loading conditions of connections by linear superposition of these foundamental load patterns. It was also confirmed that exial force applied to brace is dominant in structural strength of connection. Therefore, axial forces were mainly applied to braces in this study.Tests using several Kinds of small scale acrylic models and calculations by the FEM were carried out in order to discuss transmission mechanism of load between internal reinforcement members of connection. It was clearified by thid study that such a case where a brace penetrates column shell wall and it is supported by a hrizontal diaghragm is the most effective from stress flow and weight minimizaing view points.Buckling-collapse strength was studied by samll scale steel model tests and FEM calculations on specimens with differenct internal reinforcement members. It was concluded by these investi- gations that connections with brace penetration and internal supporting memberf of horizontal diaghragm or ring girder have relatively high resisntance to buckling-collapse. In the latter case, selection of face plate and appropriate allocation of tripping brackets for web platge of ring girder are important.By using both small and large scale steel models, fatigue tests were carried out. It was clarified that the reinforcement method mentioned above showe high resistance to fatigue. Moreover, significance of crack initiation life, through-thickness life and failure life was discussed as a general aspect of the case of specimens with complicated reinforcement members.