Experimental assessment of dynamic parameters and vibration behaviour of a reduced-scale steel frame system

The identification of dynamic parameters and vibration control are fundamental to understanding the dynamic behaviour of civil engineering structures and constructing earthquake-resistant systems. Despite previous research, a critical need remains for a deeper understanding of comprehensively determining these parameters experimentally using Frequency Response Functions (FRFs). Furthermore, there is a lack of studies investigating vibration control in multi-degree-of-freedom (MDOF) structures through the modification of their physical properties, specifically mass. This study aims to experimentally identify dynamic parameters using FRFs and investigate the vibration control performance of a three-story reduced-scale steel portal frame by adding masses to its different stories. The model is excited using a white-noise signal from a shaking table, while responses are recorded at each floor using piezoelectric accelerometers. FRFs are computed from input-output signals using spectral analysis techniques, allowing natural frequency identification from resonance peaks. Damping ratios are estimated via the half-power bandwidth method, and mode shapes are extracted using Singular Value Decomposition (SVD) of the FRF matrix. In the second part, the influence of added masses on the model’s dynamic parameters, specifically the natural frequencies and steady-state acceleration responses under harmonic excitation, was analysed. These results are compared with a finite element model (FEM) to evaluate experimental-numerical correspondence. Results show good agreement, confirming the FEM accurately reproduces the model's real dynamic behaviour. It is also observed that both the location and magnitude of added masses affect natural frequencies differently, particularly the first frequency. Moreover, optimal added mass placement significantly reduces response amplitudes under harmonic excitation. This study offers valuable insights into tuning structural frequencies to prevent resonance, especially under intense excitation, and highlights effective locations for Tuned Mass Damper (TMD) systems to improve vibration mitigation and the overall performance of MDOF structures.