A Comprehensive Study of Floor Acceleration Demands in Multi-Story Buildings

Abstract

This paper summarizes the results of a comprehensive study of floor acceleration demands on nonstructural components. The study is based on analytical studies on buildings responding elastically and nonlinearly to earthquake ground motions. Buildings analyzed range from 3 to 18 stories. Parameters evaluated include: fundamental period of vibration, lateral resisting system, damping ratio, level of ground motion intensity relative to the intensity that triggers nonlinear behavior. The study included the following aspects: (1) parametric study of peak floor acceleration demands in buildings responding elastically; (2) parametric study of floor response spectral ordinates in buildings responding elastically; (3) development of response spectrum analysis for estimating peak floor acceleration demands; (4) dynamic interaction between primary and secondary systems; and (5) peak floor acceleration demands in buildings responding nonlinearly. Results indicate that the amplitude of acceleration demands in buildings and their variation along the height are strongly dependent on the period of vibration, lateral resisting system and damping ratio of the building and therefore, current US recommendations that compute acceleration demands that are independent of the period, damping and lateral resisting are inadequate. It is also shown that alternative code procedures based on linear response spectrum modal analysis are equally inadequate. The most important trends are summarized. INTRODUCTION Nonstructural components typically represent a major portion of the total cost of buildings. Furthermore, nonstructural damage is often triggered at response intensities that are smaller to those required to produce structural damage. Therefore, it is not surprising that when losses due to structural and nonstructural components are separated, losses due to nonstructural components have consistently been reported to be far greater than those resulting from structural damage (Ayers et al. 1973a, 1973b; Whitman et al. 1973, Rihal, 1992). Recent investigations have also reported that 616 ATC & SEI 2009 Conference on Improving the Seismic Performance of Existing Buildings and Other Structures