Impact of Nonstructural Components on Modal Response and Structural Damping

Abstract

Damping in a building has significant impact on the amplitude of structural response. The trend towards lighter primary and secondary structural elements in modern buildings has led to structures being more susceptible to vibration. The level of vibration is largely dependent on the structure’s total damping, which includes structural and non-structural damping along with other factors. This paper discusses the effect of non-structural elements, on the damping characteristics of a four storey reinforced concrete structure. The dynamic properties of the test structure considered, a new build on the campus of University College Dublin, were determined by post-processing ambient and forced vibration response data measured in-situ on the first floor at various stages of construction, including prior to and post installation of non-structural elements. Post-processing of measured ambient responses was undertaken using a combination of Operational Modal Analysis (OMA) and Frequency Domain Decomposition (FDD) techniques. Three methods to calculate the damping ratio of the structure are discussed, including one in the time domain, Logarithmic Decrement and two in the frequency domain, Half-Power Bandwidth method and Enhanced Frequency Domain Decomposition (EFDD). The level of damping was found to vary as the structure evolved to completion with the highest damping values occurring at completion.