Scaled shaking table testing of higher‐mode effects on the seismic response of tall and slender structures

Abstract

AbstractAs structures are built taller and more slender, their response becomes increasingly sensitive to dynamic loads that are induced by the buildings’ higher‐frequency vibration modes. This leads to a more complex seismic response of high‐rise structures when compared to the seismic response of low‐rise structures that are primarily governed by their fundamental modes of vibration. This paper presents the results of extensive shake table testing and finite element analyses of a small‐scale, 1.5‐meter‐tall shaking table specimen that was designed and scaled to experimentally capture the higher‐mode effects of a 125‐meter‐tall reference tall building. The test specimen is comprised of a simplified superstructure with uniform mass and stiffness representing the main structure of the full‐scale reference tall building, and a base‐rocking mechanism to represent the moment‐limiting effect of the inelastic plastic‐hinging mechanism at the base of the reference building. Using the methodology proposed in this paper, the scaled specimen was shown to exhibit similar seismic response characteristics, including the corresponding higher‐mode effects, along the height of the structure as those predicted numerically on the full‐scale reference building. Results of the shaking table tests experimentally provided further evidence that relying only on a moment‐limiting mechanism at the base of a cantilever structure is insufficient in limiting peak seismic loads due to higher‐mode effects. In addition, by comparing test results with predictions obtained using several previously proposed analytical methods, the paper demonstrated that predicting shear force amplifications due to higher‐mode effects is still challenging. The methodology developed in this study can be used to design other similar small‐scale shaking table tests for the development of new analytical methods to predict higher mode effects and experimentally validate the efficiency of new high‐performance systems developed to mitigate higher‐mode effects on tall and slender structures and more generally to assess the ability of these systems to achieve enhanced seismic resilience.