Structural Health Monitoring with analysis of dynamic characteristics intends to detect stiffness changes caused by damage. It can be performed by vibrational tests resulting to modal parameters, that is, eigenfrequencies, damping, modeshapes, or modal masses. Those parameters are themselves informational and even allow often deducing the stiffness matrix. Based on that, it is possible to identify and to localize changes in the stiffness matrix due to damage, that is, localization and quantification of damage. However, changing test conditions, like ambient temperature or excitation force or existing nonlinearities of concrete, show important influence on damage indicators and hence need compensation prior to damage detection. Considering this background, this article focuses on comparing ambient excitation to forced excitation including appropriate exciters. Furthermore, continuous monitoring is discussed vs discrete testing in distinct time-intervals. The intention of the comparison is to give an overview, that is, helpful for choosing appropriate measurement technique for the sake of correct damage detection subsequently. K E Y W O R D S ambient excitation, dynamic damage indicators, forced excitation, modal analysis, structural health monitoring
Structural Health Monitoring with analysis of dynamic characteristics intends to detect stiffness
changes caused by damage. As local stiffness loss itself cannot directly be measured, the modal
parameters i.e. eigenfrequencies, damping, modeshapes with modal masses allow to obtain residua
of the transfer matrix. One row of transfer matrix is equivalent to physical description based on
mass-, damping- and stiffness-matrix, where the latter is of interest to identify and localize changes
due to damage. Today several practical options for tracking modal parameters are used. Changing
ambient temperature has important influence on modal parameters and hence on stiffness, which
should be separated from damage. Furthermore, reinforced concrete shows dependency on
excitation force, which is a non-linear phenomenon to be considered. After presenting these effects,
the paper will focus on ambient excitation compared to forced excitation including appropriate
exciters. Then continuous monitoring will be discussed versus discrete testing in distinct timeintervals.
The intention is to give an overview to localize and quantify damage later on.
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