Vertical floor acceleration spectra for regular steel frame structures

Abstract

The scope of this contribution is the assessment of the vertical peak component acceleration of single-degree-of-freedom (SDOF) oscillators attached to elastic moment-resisting steel frames subjected to recorded ground motions. These SDOF oscillators represent nonstructural components (NSCs) flexibly attached to the load-bearing structure whose acceleration demands correlate with their maximum strength demands. The results in terms of floor acceleration spectra show that the interaction between a vertically oscillating NSC and the structure is much more pronounced than for horizontally oscillating NSC of the same mass and natural frequency. This means that even for vertical NSCs with very small mass (in the case of the investigated eight-story frame 0.01% of the frame mass depending on the number of stories) a coupled analysis is required for a realistic prediction of the NSC acceleration demand. In a parametric study of vertical NSCs attached to steel frame structures of different number of stories, a median vertical peak component acceleration was observed up to 5.5 times larger than the vertical peak floor acceleration of the attachment node of the load-bearing structure and up to 20 times larger than the vertical peak ground acceleration. The amplification of the vertical acceleration response is thus of the same order of magnitude as for horizontal NSCs. This means that the vertical dynamic response of flexible NSCs cannot be neglected and should therefore be studied in more detail in the future.