| Summary: | 碩士 === 國立交通大學 === 土木工程系所 === 101 === It is common to use static cyclic loading tests to evaluate the seismic capacity of a structure. However, it is believed that different loading history resulting in different structural behavior would lead to a bias assessment of structural capacity. To quantify the effects of loading protocols for static cyclic testing on the structural capacity, we investigate the experimental behavior of brace in concentrically braced frames (CBF) under different loading protocols. Because the current AISC Seismic Provisions does not specifically provide the loading protocols for CBF, we propose one in this research based on the previously conducted nonlinear dynamic analysis of CBF structures. The variables for six brace testing includes two different pipe sections (different slenderness as well) and three loading protocols, namely, Loading Sequence for Beam-to-Column Moment Connections（AISC, 2010）, Loading Sequence for Link-to-Column Connections（AISC, 2010） and Proposed Loading Sequence for CBF. After tests, we compare the performance parameters of different specimens including the strength, deformation, cumulative energy and cumulative deformation of braces when critical failure modes occur. Test results show that the brace specimens fracture at different deformation stages in different loading history; most brace specimens fracture at the displacement corresponding to the drift ratio of 1.5% to 4%. On the other hand, the cumulated energy is less correlated to the loading history; the specimens with the same D/t and KL/r tend to have similar cumulated energy regardless of the applied loading history. It is difficult to estimate the deformation related capacity of the braces by employing the Loading Sequence for Beam-to-Column Moment Connections without any modification. However, it is possible to capture the energy related capacity of the braces by any of the three tested loading protocols. If the deformation related capacity of the braces is the parameter of interest, we can use Loading Sequence for Link-to-Column Connections and Proposed Loading Sequence for CBF to estimate it. While brace specimens under both Loading Sequence for Link-to-Column Connections and Proposed Loading Sequence for CBF show consistent seismic performance, failure modes and energy dissipation behavior, the Proposed Loading Sequence for CBF is more suitable for braces in terms of deformation amplitude, and number of cycles at elastic and plastic deformations.
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