Seismic Energy Response of Multi-Story Steel Rocking Frames Allowing Column Mid-Height At the First Story

Abstract eng:
Observations from past earthquakes suggest that some buildings survived severe ground motion because of accidental uplift at their foundation. Such notion has motivated the development of rocking systems that permit some portion of the structure to uplift and rotate about a pivot. In this paper, the writers propose a rocking frame that allows uplift at the middle of the columns. The column mid-height uplift (CMU) mechanism fully resists shear forces and is generally accompanied by steel dampers. A series of nonlinear time history analyses was conducted on a model of a four, six and ten-story steel buildings equipped with CMU mechanisms. The CMU mechanisms was modeled using (1) a contact element (that permits uplift but resists compression), (2) a linear shear element, and (3) a bilinear element (that models steel dampers). The models were subjected to seventeen recorded ground motions, each scaled to a maximum ground velocity of 1.0 and 1.25 m/s. For comparison, the analyses were repeated for models where the bilinear elements were removed (CMU-ND model), and models where the first-story columns were continuous with no contact element (MF model). The results are summarized as follows: (1) Little difference was observed between the CMU model and MF model in terms of maximum roof acceleration. (2) Maximum roof drift was significantly smaller in the CMU model than in the CMU-ND model, especially if structure have high aspect ratio. (3) Energy dissipated by the steel system was significantly smaller in the CMU model than in the MF model.

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