Analytical and experimental investigation into dynamic properties of glued–laminated (glulam) beams reinforced with various lay ups of e-glass reinforced epoxy polymer (GRP) composites are discussed. Three unreinforced glulam (control) beams and 11 glulam beams reinforced with GRP on their bottom surface were clamped in a cantilever condition and tested using an instrumental hammer. The natural frequencies of all beams determined by the impact dynamic (hammer) method using power spectral density (PSD) were used to estimate damping ratio of all the beams through both time domain and frequency domain methods. In the time domain analysis, the method of logarithmic decrement analysis (LDA) and the Hilbert transform analysis (HTA) were considered; in the frequency domain analysis, both moving block analysis (MBA) and half-power bandwidth (HPB) were applied to the data and a new approach HPB method with a polynomial correction function was numerically established. A comparison between the results obtained from all the methods of analysis and a new approach shows that this method may improve the accuracy of the HPB method in evaluation of vibration damping properties of glulam reinforced composite beams because glulam beams have high level damping ratios and that this method should be modified especially when used with materials having high level damping ratios.
Mixed Time/Frequency-Domain Based Robust Identification
