1,720,979 research outputs found
Vibrations of steel-concrete composite beams with partially degraded connection and applications to damage detection
No full textVibrational methods are frequently used as diagnostic tools to detect damage in structures. One of the main
difficulties connected with the use of such methods lies in the small sensitivity of the dynamic parameters to
damage. This is an intrinsic feature of structural diagnostics based on dynamic data. It represents a source of
important indeterminacy, such as the strong dependence of the results of identification on the experimental errors
and on the accuracy of the structural model that is chosen to interpret measurements. Application of dynamic
techniques to the case of steel-concrete composite beams, in addition, makes the problem more complicated, owing
to the uncertainty about the mechanical behaviour of the connection and damage modelling. Previous research on
vibrational methods for damage detection in composite beams was concerned with the identification of severe levels of
damage. In this paper we present an Euler-Bernoulli model of composite beam which accurately describes the dynamic
response measured on composite beams with either severe or intermediate levels of damage. A diagnostic technique
based on frequency measurements is then applied to the suggested model and gives positive results. A Timoshenko
model of composite beam is also derived and used for diagnostic purposes
A damage analysis of steel-concrete composite beams via dynamic methods. Part II: Analytical models and damage detection
No full textThis paper is the second part of an experimental-analytical investigation on the dynamic behavior of damaged steel-concrete composite beams. In the first part of the research, experimental results of a comprehensive series of dynamic tests performed on composite beams with damage in the connection were presented and discussed. Experimental observations suggested the formulation of a composite beam analytical model, where the strain energy density of the connection also includes an energy term associated to the occurrence of relative transversal displacements between the r.c. slab and the steel beam. A comparison with experimental results shows that the model enhances accuracy in describing the undamaged state of composite beams and that it is also appropriate to accurately predict the dynamic behavior under damaged conditions. A damage detection technique based on the measurement of variation in the first flexural frequencies was then applied to the suggested model and gave positive results
Damage detection in discrete vibrating systems
No full textThis paper deals with the identification of a single defect in a
discrete spring-mass or beam-like system by measurements of
damage-induced shifts in resonance frequencies and antiresonance
frequencies. For initially uniform discrete systems, it is shown
how the measurement of an appropriate set of frequencies and
antiresonances permits unique identification of the damage. The
theoretical results are confirmed by comparison with numerical and
experimental tests
Damage identification in beams from changes in nodes of mode shapes
No full textIt is known that the effect of a single crack in an axially vibrating rod is to cause the nodes of the mode shapes move toward the crack. In this paper an investigation of the analogous problem for a beam in bending vibration is presented. The monotonicity property linking changes in node position and crack location does not hold in the bending case. The analysis of the direct problem, however, shows that the direction by which nodal points move may be useful for predicting damage location. Analytical results agree well with experimental tests performed on cracked steel beams
Identification of crack location in vibrating beams from changes in node positions
No full textIt is known that the effect of a single crack in an axially vibrating thin rod is to cause the nodes of the mode shapes move toward the crack. This paper is an analytical/experimental investigation of the analogous problem for a thin beam in bending vibration. The monotonicity property linking changes in node position and crack location does not hold in the bending case. The analysis of the direct problem, however, shows that the direction by which nodal points move may be useful for predicting damage location. Analytical results agree well with experimental tests performed on cracked steel beams
Detecting cracks in a longitudinally vibrating beam with dissipative boundary conditions
No full textThis paper focuses on detecting a small open crack in an axially vibrating beam with viscous boundary conditions by using non-destructive dynamical measurements. The damage is simulated by an equivalent linear elastic spring. It is shown that the measurement of the changes in a suitable pair of eigenvalues leads to the solution of the diagnostic problem, namely identification of crack location and severity. Results apply to uniform beams under various sets of boundary conditions
On point mass identification in rods and beams from minimal frequency measurements
No full textThis paper deals with the identification of a small mass point in a vibrating rod based on the knowledge of the variations induced in a pair of natural axial frequencies. The analysis is based on an explicit expression of the frequency sensitivity to point mass variations and allows consideration of non-uniform bars under general boundary conditions. The inverse problem is generally ill-posed, that is, even if the system is not symmetrical, mass points in different locations can still produce identical changes in a pair of natural frequencies. Despite this ill-posedeness, it is found that there are certain situations concerning uniform rods in which the effects of the non-uniqueness of the solution may be considerably reduced by means of a careful choice of the data. Some of the results are also valid for beams in bending and the identification technique can be extended to include the case of two equal point masses. The theoretical results are confirmed by a comparison with dynamic measurements on steel beams with one and two point masses
Structural health monitoring of rods based on natural frequency and antiresonant frequency measurements
No full textIn this paper it is shown that natural frequency and antiresonant frequency shifts induced by a structural damage in an axially vibrating rod contain information on certain generalized Fourier
coefficients of the stiffness variation caused by the degradation.
This property is used to define a reconstruction procedure based on iterative updating of the undamaged configuration. The results
of numerical simulations on rods with localized or diffuse damages are in good agreement with the theory, provided that average frequency and antiresonant frequency shifts due to degradation are
bigger than the shifts due to modeling/measurement errors.
Experimental results obtained on cracked steel rods showed that, in the inverse problem solution, noise and modeling errors on antiresonances are usually amplified strongly with respect to cases in which natural frequency data is used
The use of antiresonances for crack detection in beams
No full textThis paper deals with the identification of a single open crack in a vibrating beam, either under axial or bending vibration, based
on measurements of damage-induced shifts in natural frequencies and antiresonant frequencies. It is found that an appropriate use of frequencies and antiresonances may avoid the non-uniqueness of the damage location problem, which occurs in symmetrical beams
when only frequency data are employed. The theoretical results are confirmed by a comparison with dynamic measurements on cracked
steel beams under free-free boundary conditions
Reconstruction Method for Damage Detection in Beams Based on Natural Frequency and Antiresonant Frequency Measurements
No full textThis paper deals with a dynamic method for damage detection in
beams. Under the assumption that the damaged beam is a
perturbation of the undamaged one, it is shown that natural
frequency and antiresonant frequency shifts induced by structural
damage contain information on certain generalized Fourier
coefficients of the stiffness variation caused by the degradation.
A reconstruction method based on this property is proposed to
solve the inverse problem. Cases with pseudoexperimental and
experimental data are discussed. The results are in good agreement
with the theory, provided that average frequency and antiresonant
frequency shifts are bigger than modeling/measurement errors
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