Flexural demand of columns in Special Moment Frames

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2017-01-01
Authors
Hadjiyiangou, Michailina
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Jiehua J. Shen
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Civil, Construction, and Environmental Engineering
Abstract

This study investigates the flexural demand in columns in the following contexts: the demand on the column splice, the flexural demand distribution (bending moment diagram) shape, and the moment distribution at beam-column joints. Incremental dynamic analysis (IDA) was carried out for a 15-story special moment frame subjected to 20 different ground motions. A newly developed demand-chain concept was employed together with IDA in assessing the seismic demand on column splices and strong column-weak beam mechanism, based on inelastic deformation demand on beam-to-column joints at three performance levels, the immediate occupancy (IO) level, the life safety (LS) level and the collapse prevention (CP) level at 2%, 4% and 6% of story drift ratio (SDR) respectively. The demand on column splice was evaluated in terms of peak normalized axial ratio, peak flexural ratio, and maximum combined axial and flexural demand-to-capacity ratio. This investigation concludes, with a combined IDA and demand-chain concept, that the flexural demand on the splice can reach as high as the nominal strength of the smaller section when the structure is subjected to the design earthquake. This study also presents systematically single curvature deformation patterns in the columns in contrast to the perfect double curvature (PDC) assumption used in code-based design of steel moment frames. Furthermore, this work reveals that plastic hinges may occur in the columns near beam-to-column joints when the frame is subjected to the life safety (LS) level of earthquake ground motions. This finding presents a challenge to the current methodology used in enforcing strong column-weak beam behavior in earthquake-resistant moment frames.

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Sun Jan 01 00:00:00 UTC 2017