Code-oriented floor acceleration spectra for building structures

Abstract

In the seismic design and assessment of acceleration-sensitive equipment installed in buildings, floor acceleration spectra, which are based on an uncoupled analysis of the structure and the equipment, are usually used. However, in order to obtain an “accurate” determination of floor spectra, a complex and quite demanding dynamic response-history analysis is needed. Recently a method for the direct generation of floor acceleration spectra from ground motion spectra, taking into account the dynamic properties of the structure, has been developed and validated. It is based on the theory of structural dynamics, in combination with empirically determined values for the amplification factors in the resonance region. The method can be used for both elastic and inelastic multi-degree-of-freedom structures and equipment modelled as an elastic or inelastic single-degree-of-freedom oscillator. In the case of inelastic primary structures, the method is coupled with the pushover-based N2 method. The variant of the method which is presented in this note is intended for practical applications, e.g. for implementation in guidelines and codes, and it represents a simplified version of the original method. In addition to some simplifications, the option of taking into account the inelastic response of the equipment was added. In the note, the method is summarized, and all the formulae needed for the calculation of floor acceleration spectra are provided. A description of all steps of the analysis, together with all the relevant numerical data, is presented in a test example.