| Research Abstract |
CFT frames consisting of concrete-filled steel tube (CFT) columns and pure steel beams have become very popular these days, since it has been verified by many investigations since 1970's that GET columns have more benefit compared with ordinary steel columns. This is mainly because of the interactive effects between steel and concrete ; the confining effect of the steel tube on the concrete, and the restraining effect of filled-concrete on the local buckling of the steel tube. The behavior of the beam-to-column connections, including new type of diaphragm system, were also investigated experimentally. However, very few frame tests have been done.
In order to clarify the elasto-plastic behavior of GET frames under seismic loading, portal frame specimens were tested under constant vertical loads on columns and alternately repeated horizontal load. Experimental parameters were as follows : axial load ratio(0.15, 0.3 and 0.5), width-to-thickness ratio (21 [rank A], 39 [rank C]and 54[rank D]
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), and yield mode (column-yielding type and panel-yielding type). The cross sections of columns and beam were *-125x125xt and BH-150x125x6x9, respectively, and column height and beam length were 1,000 and 1,500 mm, respectively, The following observations were made from the test results : 1) Hysteretic behavior was quite stable, except the specimens in which fracture occurred at the welding between the column tube and the connection diaphragm ; 2) The local buckling of either the column or the connection panel did not affect much the maximum strength and the deformation capacity ; 3) The maximum strength of frames consisting of D-rank column tube was determined by the local buckling, and it did not reach the value calculated from the formula specified in AIJ Standard, but the strength deterioration was gentle and the behavior was stable ; and 4) The value of Ds was quite well improved by filling the concrete in the column tube, but this effect was not very clear in the case of panel-yielding specimens.
Test data of CFT beam-columns and frames were collected from the Japanese literatures published in1972 through 1997, and databases were developed and maintained. Number of test data (test specimens)collected were as follows : 1) Columns : 242 square GFT, lll circular CFT, and total 353 ; and 2) Frames : 184square GFT, 52 circular CFT, and total 236. From these databases, evaluation formulas for the deformation capacity and Ds factor and models for the restoring force characteristics were proposed for both GET columns and frames, and the accuracy of those formulas and models was investigated in view of the test results. Less
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