| Summary: | 碩士 === 國立成功大學 === 土木工程學系碩博士班 === 100 === In this study, the structural steel SN490B was heated to 900℃, and then was cooled down by air and water respectively to simulate two kinds of cooling situations for steel structures after fire. Three groups of round bar specimens, including non-fire damaged group, air-cooling group and water-cooling group, were manufactured for cyclic loading test. The two specimens in each group were tested by constant-strain and increased-strain cyclic loading histories respectively to understand the possible cyclic behaviors of high-temperature fire damaged SN490B steel and to acquire the related hardening parameters. The test results showed that cyclic hardening occurred in the non-fire damaged and air-cooling steel and the yield stress of the air-cooling steel decreased 16.75%. Cyclic softening occurred in the water-cooling steel and the yield stress of the water-cooling steel increased 47.62%. Besides, this study also developed the nonlinear finite-element models for five common beam-to-column connections, i.e. traditional connection, cover-plate connection, side-plate connection, radius-cut flange profile connection and tapered flange profile connection, in Taiwan. The hardening parameters acquired from the previous cyclic loading tests were substituted into the nonlinear finite-element models to perform the numerical simulations of the cyclic loading experiments for the five common beam-to-column connections after high-temperature fire. The numerical simulation results showed that the beam flexural resistance at the column face for each air-cooling connection was lower than the nominal plastic moment at column face (Mf) of each associated non-fire damaged connection for the reason of slightly decreased strength of air-cooling steel, but still could meet the two AISC deformation and flexural strength requirements for beam-to-column connections in special moment frames. All the water-cooling beam-to-column connections fractured at the beam-to-column welds, and could not meet the AISC plastic deformation requirement for beam-to-column connections in special moment frames.
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