Internal Force Transmission and Stiffening Effeciencv of Stiffened Joints for Offshore Structures

Abstract

A number of papers on structural mechanics and strength of tubular joints of offshore structures have been published. Most papers of them treated simple nonstiffened joints and only small number of papers treated stiffened joints of members with small diameter, where simple gussets or ring stiffeners were used as stiffening elelmets.Foundamental knowledges are needed, which are useful to initial design of stiffened joints of a large diameter member with small diameter members such as column to brace jojnts in semisubmersibles.In this paper, effects of several kinds of stiffening elements used in joints mentioned above are discussed by both experiments using acrylic models and numerical calculations using a FEM program newly developed for the purpose of behavior analysis of shell structures with complicated construction. The joint models mainly discussed are T type of joints subjected to axial load of brace. A TY type of joint model is also studied experimentally and theoretically. The types of stiffening elements used in the models were diaphragm, vertical bulkhead, ring girder, vertical girder, piercing brace and so on. Each specimen of joint was fabricated as combination of a standard non-stiffened joint structure and a set of stiffening elements inserted in a chord member of the joint.Finally, taking weights of stiffening elements into consideration, stiffening efficiency of joint models treated are compared. This comparison resulted in such a conclusion that a joint stiffened by a diaphragm and a partially piercing brace is the most effective as a T type of jojnt.