Vertical System Identification of a 52-Story High-Rise Building Using Seismic Accelerations

Abstract

In this study, various system identification approaches are utilized to estimate the dominant,
vertical-component modes of a 52-story, steel, moment-and-braced frame building in downtown Los
Angeles resulting from vertical seismic accelerations. Tall buildings exhibit complex threedimensional
responses during an earthquake due to the varying material and geometric properties
along the building’s height. For high-rise buildings, the dynamic response during shaking events is
often sensitive to multiple vibration modes, and multiple-mode structural behavior under horizontal
ground motion has been extensively studied. However, the vertical component of ground motion can
also excite higher modes and vertical-polarity propagating seismic waves. Their effects are seldom
studied due to the scarcity of data. Still, they are important because they can provide information on
the axial loads on columns or stresses at floor slab connections. The 52-story high-rise, with its dense
triaxial sensor array distributed vertically along the height of the building, provides a suitable basis
for examining vertical responses. System identification is performed using state-space methods with
low-amplitude earthquake data. Given the high spatial density of the building recordings, we show
how we can detect modal characteristics and identify the type of deformation that can occur when
considering the vertical component of seismic responses.

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