Abstract
The progressive change of modal characteristics due to accumulated damage on an unreinforced masonry (URM) building is investigated. The stone URM building, submitted to five consecutive shakings, has been experimentally studied on the shaking table of EUCENTRE laboratory (Pavia, Italy). The dynamic characteristics of the test specimen are analytically estimated using frequency and state-space modal identification from ambient vibration stationary tests carried out before the strong motion transient tests at various levels of damage. A singular value (SV) decomposition of the cross-correlation matrix of the acceleration response in the frequency domain is applied to determine the modal characteristics. In the time domain, the subspace state-space system identification is performed. Modal characteristics evolve from the initial linear state up to the ultimate collapse state in correlation with accumulated damage. Modal frequencies shorten with increasing intensity, whereas modal damping ratios are enhanced. Modal shapes also change with increasing level of accumulated damage. Comparing the evolution of modal characteristics, it is concluded that modal damping ratio shift can be better correlated with the system’s actual performance giving a better representation of damage than that of natural frequency shift ratio or the modes difference.
Highlights
During strong seismic vibrations, the dynamic characteristics of structures undergo changes. ree properties of a structure, i.e., mass, damping, and stiffness, influence its dynamic parameters which are natural frequencies, modal damping, and mode shapes
Structural damage leads to modification of the modal stiffness and damping and mode shapes and to the dynamic characteristics. is process can take place even due to low to moderate shaking of a structure [1, 2]
The dynamic identification in the frequency domain using, for example, the frequency domain decomposition (FDD) [8, 9] or the peak-picking method (PP) can be sufficient to Advances in Civil Engineering detect the dynamic properties through global modal analysis
Summary
The dynamic characteristics of structures undergo changes. ree properties of a structure, i.e., mass, damping, and stiffness, influence its dynamic parameters which are natural frequencies, modal damping, and mode shapes. Ree properties of a structure, i.e., mass, damping, and stiffness, influence its dynamic parameters which are natural frequencies, modal damping, and mode shapes. Structural damage leads to modification of the modal stiffness and damping and mode shapes and to the dynamic characteristics. A shaking table experiment has been performed applying an incremental and consecutive procedure: five timehistories of a scaled real recording are used to shake the structure up to a near collapse damage state. In this series of tests, damage is accumulated influencing the natural properties. It is similar to the macroseismic intensity which is defined in terms of the response and the observed damage of the buildings. e frequency shift ratio, the damping shift ratio, and the modal shape difference from test phase-to-test phase are compared
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