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.