Investigation of the Distribution of Cumulative Ductility Demand Parameter in Various Stories of Buckling Restrained Braced Frames

Due to the fact that the buckling-restrained brace core yields both in tension and compression, it can absorb energy and exhibit high ductility rendering it proper for tolerating earthquake loads. One of the important objectives of seismic standards is providing the appropriate ductility for the structures, because the structures, in case of being ductile, can depreciate a considerable amount of earthquake energy. According to the importance of the issue, the present study makes use of cumulative ductility parameter as a scale that is practically applied to describe the plasticity demand of the buckling restrained brace (BRB) member to investigate the cyclic behavior of the braces and buckling restrained braced frames (BRBF). For this purpose, nonlinear time history analysis was run on three steel buckling restrained braced frames in three different height rates, namely 5-story, 10-story and 15-story, subject to seven earthquake records in OpenSees Software. Using the results of the analysis, hysteretic curves were delineated for the stories and cumulative ductility demand and hysteresis energy parameters were calculated for each of the obtained curves. The results indicated that the cumulative ductility demand distributions of the stories of the buckling restrained braced frames, designed corresponding to AISC360 guidelines are not identical and that higher ductility demands were scored for the upper stories. The stories with more cumulative ductility demand should be redesigned for larger brace cross-sections, although, in terms of strength, the cross-sectional area of the bracing does not require to be larger.