In order to ensure sufficient structural safety of offshore floating structures under severe environment, it is important to clarify the buckling and collapse strength of joints between structural elements such as columns, lowerhulls, decks and bracings. Especially, joints between columns and bracings are in higher stress-level in waves and their collapse may lead to overall collapse of structures. In general, as columns and bracings, thin-walled tubular members with large diameter are used. So, joints between them are reinforced by several reinforcements such as girders, diaphragms, bulkheads and inserted bracings et cetera. The purposes of this study are investigation of buckling and collapse strength of several types of reinforced tubular joints and evaluation of effective patterns of reinforcement. In the present paper, as a first step, experimental and theoretical studies on the buckling and collapse behavior of T-type tubular joints reinforced by girders and/or inserted bracings under compression are carried out. Basic mechanism of transference of loads into interior of joints are also investigated and simplified model for calculation of internal forces in ring girders is proposed.