Modelling effect of non-structural partitions on floor modal properties

Abstract

Non-structural cladding and partitions can have significant stiffening effects on the vertical vibration behaviour of floors in buildings. Such effects are currently difficult to quantify and use in design. To quantify them, modal properties of two structurally identical full-scale floors in a real fitted-out building were measured and compared to results for the same floors prior to installation of the internal partitions and cladding panels. In its bare frame state the modal properties of both floors were found to be nominally identical. However, when tested after the installation of internal partitions and external cladding panels, it was found that the addition of these non-structural elements increased the stiffness of both floors and also altered significantly their modes of vibration, in particular natural frequencies and mode shapes. The fundamental natural frequencies increased by 30% for both fitted out floors relative to their bare state. However, the change in modal properties varied from floor to floor and this difference was attributed to the differing partition layouts on and below each floor. This paper also proposes a numerical modelling approach to account for these effects. The measured modal properties of the structural system in its bare frame state were used initially to update a three dimensional Finite Element (FE) model of the bare multi-storey frame system featuring the tested floors. Linear elastic spring elements were subsequently included representing the internal partitions and external cladding panels. The bare frame FE model was further updated to determine appropriate spring constants by correlation with modal parameters measured on the fully completed building. For the particular type of cladding and partitions used, it was found that the cladding vertical stiffness is about twice its partitions counterpart. Also, and as expected, the vertical stiffnesses estimated through this process were lower than, but comparable with, the stiffnesses of these elements based on their ideal cross-sectional properties.