Abstract
The scope of this study is the quantification of vertical peak floor acceleration demands at column lines and along the length of beams of elastic moment-resisting steel frames subjected to recorded ground motions. These demands correlate with the maximum strength demands on rigid nonstructural components attached to a frame structure. Since it is commonly assumed that buildings behave flexibly in the horizontal direction and rigidly in the vertical direction, the assessment of vertical acceleration demands is typically not considered in most cases. The results of this study show that vertical peak floor accelerations can be up to five times larger than the vertical peak ground acceleration, in contrast to horizontal peak floor accelerations that are only up to two times larger than the horizontal peak ground acceleration for the numerical models used in this study. The most significant amplifications estimated in the vertical direction are found at the center of the girders. Further investigations of modified steel frames indicate that the story-wise mass distribution has an influence not only on the vertical acceleration demand, but also on the horizontal component of the response, though to a lesser degree. In contrast, the response in the vertical and horizontal direction is only slightly affected by an increase in the flexural stiffness of the beams. The results of this study strongly indicate that in steel frames it can be considered highly questionable to ignore the amplification of the vertical acceleration component along the height of the structure.
Highlights
Several seismic events of the last decades left many buildings not operational the load-bearing structure remained virtually unimpaired
The analyses are conducted in OpenSees (McKenna et al 2014) by imposing simultaneously the horizontal and vertical ground motion components of the considered horizontal ground motion (HGM) and VGM record sets, respectively
Recent studies have indicated that in elastic mid- and high-rise steel moment resisting structures the filtering effect of the building can significantly amplify the vertical peak ground acceleration (PGAv) along the height. This conclusion is in contrast to the common assumption that the vertical peak floor acceleration (PFAv) demand is constant along the height of a structure
Summary
Several seismic events of the last decades left many buildings not operational the load-bearing structure remained virtually unimpaired. Further research was conducted by Ryan et al (2016), who studied experimentally the vertical peak accelerations of a full-scale, 5-story steel building These few studies, including a preliminary investigation of the authors (Gremer et al 2018), do not provide an in-depth understanding of the relationships between frame parameters (such as number of stories, mass and stiffness distribution, etc.), horizontal and vertical base excitation, as well as horizontal and vertical acceleration response demand in seismically excited buildings. The objective of the present contribution is to evaluate parametrically the vertical peak floor acceleration normalized with respect to the corresponding peak ground acceleration component (PFAv/PGAv) of the column lines and of the beams of elastic steel moment resisting frames. The differences between the vertical and horizontal responses are evaluated
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