Effect of Vertical Accelerations on Steel Frame Structures

Abstract eng:
It is a well-known fact that all earthquakes have three orthogonal components of acceleration including two horizontal and one vertical acceleration. Current design practice for design of structures in the United States only focuses on the impact of the horizontal component of earthquakes. However, according to previous research, vertical peak ground acceleration (PGA) can be higher than the horizontal peak acceleration in the same earthquake, which may contribute to structural damage or collapse. Further research is needed to investigate the impact of vertical ground motion on seismic response of structures. In this paper, a six-story steel frame structure is chosen to investigate and represent this problem. Two special moment frames with reduced beam section (RBS) connections are designed by the equivalent lateral force (ELF) method based on ASCE 7-10 and analyzed using nonlinear dynamic analysis. In this study, a suite of 20 ground motions were selected from the far-field and near-field suites of recorded ground motions from FEMA P695 which include horizontal and vertical ground motions. The range of the ratio of vertical to horizontal acceleration in this study is from 0.5 to 1.2. All the structural models are analyzed under two different loading cases: 1) Horizontal Only and 2) Horizontal plus Vertical. The impacts of the vertical accelerations had little impact on the lateral drift of the structure but had a significant impact on the axial forces in the columns.

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