Nonstructure–structure interaction with respect to mass ratio: Numerical analysis and free vibration tests

Abstract

The dynamic interactions between nonstructural components (NCs) and the main building structure cannot be neglected because the dynamic properties of the main structure are modified, particularly for heavy NCs. The mass ratio (MR) is a parameter that incorporates the nonstructure–structure interaction (NSI) between the NCs and main structure. In this study, to investigate the seismic interaction in terms of the MR, a four-story steel moment frame was constructed and free vibration tests were carried out. The equivalent mass of the NCs was connected to various floor levels, neglecting their stiffness and damping. The vibration mode and period of the steel frame were obtained numerically. At MR = 25 %, the period generally increased with increasing MR. The modal contribution factors in terms of the roof displacement and base shear were analyzed. The findings show that it would be safe to consider the 1st mode only when using the roof displacement, whereas more modes should be considered when the base shear is used. The experimental damping ratios correlated with the magnitude of the MR without a representative trend. The damping ratio generally increases with an increase in the number of floors hosting additional masses. The experimental period increased almost linearly with the MR irrespective of the number of floor-hosting masses. An equivalent single-degree-of-freedom model is developed to predict the frame period. The predicted periods generally matched the experimental results. The normalized height of the equivalent model and period ratio vary with the MR and are correlated with the number of floors hosting the mass. The results of this study will be beneficial for the seismic design of building structures with heavy NCs.