Font Size: 

Vibration-based Structural Health Monitoring methodologies have been developed in many different applications for the aim of damage diagnosis. Recently, completely data-driven methods have been used because these methods do not assume any linearity or model in their analysis. Data-driven methods use the measured vibration signals as a data-input to subtract features that can conclude in useful information for damage diagnosis. In this work is presented a methodology based on Singular Spectrum Analysis (SSA) which decomposes the vibration responses in a certain number of principal components having in consideration all rotational patterns at any frequency. One of the steps of the methodology is to create a reference state where the observations can be compared for damage assessment. The data used to create the reference state determines how the information is represented in the reference state and therefore how meaningful and informative are the feature vectors for damage assessment. Therefore, this study presents the effects on the creation of the reference state when the data is introduced in the time or frequency domain. The results obtained are different for each case and hence they should have different interpretation when the state is created based on vibratory signals represented in the time or frequency domain.