Nadia GREMER

"Vertical acceleration demands in earthquake excited planar steel frames"

"Traditionally earthquake engineering has been concerned primarily with the assessment
of the horizontal response of load-bearing structures, because the structure is in general
in vertical direction relatively stiff. In the last decades, however, the effect of the vertical
ground motion component on buildings has been controversially discussed. While in the
past the focus was on the prediction of relative response quantities (i.e. measured relative
to the motion of the foundation) such as displacement and internal force, more recently
the importance of the total acceleration response has been recognized. The reason is
that seismic induced damage of stiff nonstructural components (NSCs) is directly related
to the total acceleration of their attached point at the load bearing structure. Several
studies examined the horizontal peak floor acceleration (PFA) demand of structural
systems. However, there is no comprehensive study on vertical PFA (PFAv) demands
of frame structures considering also the behaviour of flexible beams.

In this Master’s thesis the PFAv demand of steel moment-resisting frames excited by
earthquakes is assessed. In particular, the PFAv demand at column lines and along the
beams of various appropriate generic planar multistory frame models varying the number
of stories, fundamental periods and di↵erent refinement of discretization of the beams
is predicted based on response history analysis. The outcomes are presented in terms
of ratio PFAv over the vertical peak ground acceleration (PGAv), and they illustrate
the amplification of the PGAv in vertical direction. Assuming that NSCs are rigid, the
PFA of the frames correspond to the peak acceleration of attached NSCs.

An important conclusion of this thesis is that the median PFAv demand is up to five
times larger than the corresponding PGAv. Thus, the examined structures have no rigid
behaviour in vertical direction, and in the seismic assessment of acceleration sensitive
NSCs the PFAv demand should be considered."

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