A STUDY ON ASEISMIC PROPERTIES OF MOMENT-RESISTANT FRAMES WITH CONCRETE-FILLED TUBULAR BRACINGS

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The objectives of this study are (1)to make clear the proper details of joints for concrete-filled tubular bracings (CFT bracings) ; and (2) to discuss about an estimation method of the aseismic properties of moment-resistant frames with the CFT bracings. In l996, monotonous compression and tension tests have been conducted for the models of fiat gusset plate joints, cross-shaped gusset plate joints, and flange joints. The experimental parameters are the wadged lengths of the gusset plates and the diameter-to-thickness ratios (D/T ratios) of tubes. The test resulted that every type of the joint could have the joint effciency of 85%, if the wedged length would be larger than the specified values for the joints ofhollow tubular members. The deformability of the CFT bracings could be also realized by every type of joints. In l996 and l997, a cyclic loading test has been conducted for the CFT bracings. In the test, the cracks or breaking failures were observed in tubes but not in the joint … More s. Therefore, it can be said that every type of joints stands the cyclic axial loading. Adding to that, the loading cycles at which the crack or breaking happened in tubes could be accurately predicted by the Authors, estimation method. In l997, a horizontal cyclic loading test has been performed for the two moment-resistant portal frames with CFT bracings which tubes' D/T ratios were 20 (frame A) or 30 (frame B). The frame A specimen showed an anti-symmetrical one of the plastic collapse mechanisms. In the mechanism, one of a pair of bracings buckled but the other never buckled. The frame B specimen formed a symmetrical mechanism in which both of the bracings buckled. The symmetrical mechanism may be preferable because the energy dissipation could be expected for both the bracings. The anti-symmetrical mechanism is an unique phenomenon in a frame with CFT bracings but never in a frame with hollow tubular bracings. In terms of the energy dissipation, a frame with CFT bracings may be more advantageous than that with hollow tubular bracings, because one of a pair of bracings would contribute the energy dissipation at least. Less