No abstract is provided for this article.
Recently a new technique for Operational Modal Analysis was proposed and validated. This technique makes use of transmissibility measurements only. In general, the poles that are identified from transmissibility measurements do not correspond with the system’s poles. However, by combining transmissibility measurements under different loading conditions, it has been shown that the model parameters still can be identified. For comparison and validation, this new method and an existing output-only technique using the power spectra will be applied to operational data of a bridge. The advantage of the recently proposed technique is that the operational forces are no longer assumed to be white noise. They can be arbitrary (colored noise, swept sine, impact ...) as long as they are persistently exciting in the frequency band of interest.
An augmented Kalman filter for force identification in structural dynamics is developed, in which the unknown forces are included in the state vector and estimated in conjunction with the states. Noise is modeled as a stochastic process and is assumed to be present not only on the measurements, but also on the state variables, thus accounting to some extent for modeling errors. This distinguishes the proposed technique from purely deterministic methods for force identification in which no errors are assumed on the states. To analyze the effect hereof on the quality of the identification, the results obtained with a commonly used recursive least-squares method, the Dynamic Programming algorithm, are compared to those obtained using the augmented filter in a laboratory experiment on an instrumented steel beam. It is shown how, in the collocated case, more accurate results can be obtained with the augmented filter due to its incorporation of modeling errors. In the non-collocated case, however, better solutions are produced by classical deterministic methods as Dynamic Programming in which only the forces are estimated, and not the states as well.
Focusing on the application for diagonal braces, tie-bars and short thick cables, this work proposes a new technique to identify the axial force of a two-dimensional Euler–Bernoulli beam member. Bending stiffness effects are taken into account. On the basis of the dynamic measurements from at least five sensors, the proposed method is capable of estimating the axial force as well as the translational and rotational stiffness at both beam ends. When fixing some end constraints, the required number of sensors can be reduced. Finite element simulations are performed for verification purpose, accounting for a wide range of bending stiffness. A laboratory experiment is conducted to investigate the feasibility and accuracy of the proposed method.
Headed shear studs are commonly used to resist longitudinal shear forces in composite railway bridges. Due to the growth of traffic and increase in train speed, these studs are subjected to high-cycle fatigue loading which may lead to damage, thus affecting the integrity between the steel girder and the concrete slab. Therefore, it is necessary to find a corresponding nondestructive damage detection method. Within the frame of this paper, the occurrence of damage in shear studs is studied by numerical analysis. In the numerical model of a real composite bridge, headed shear studs are represented by spring elements. A damage indicator based on the local modal curvature and the wavelet transform modulus maxima is proposed for stud damage identification. The efficiency of the damage indicator is investigated by means of numerical simulations where different levels of damage are introduced to the stud by decreasing the spring stiffness. It is verified that the proposed damage index can be used to locate and to quantify the damage.
No abstract is provided for this article.
Statistical energy analysis (SEA) is a standard approach to high-frequency vibro-acoustic analysis that relies on a conceptual division of the system into subsystems that are assumed to carry a diffuse field and to be weakly coupled. The weak coupling assumption means that the exchange of energy between subsystems can be described in terms of their uncoupled free vibration modes. In this work, a criterion is derived for assessing the coupling strength in the general case where the subsystems are rigidly coupled and/or via deterministic linear dynamic components. The criterion is elaborated such that it can be directly evaluated from quantities that appear in the SEA power balance. In this process, the hybrid deterministic-SEA approach is employed such that subsystems and connections of arbitrary complexity can be tackled in a rigorous way. In one of its approximate forms, the proposed general coupling strength criterion reduces to the gamma criterion that has appeared in the literature for assessing some special cases of coupling. The criterion is validated with a numerical example involving two diffuse plate subsystems connected via a deterministic beam, whose dynamic behaviour influences the coupling strength.
Among the compendium of highway civil infrastructures built in the last decades, many repetitive or quasi-periodic configurations can be found, such as multi-span simply supported bridges. Structural Health Monitoring (SHM) strategies for this kind of structures should properly consider such structural periodicity. Literature studies already demonstrated that multi-span bridges are particularly challenging target structures for Operational Modal Analysis (OMA) since the modal properties typically appear as dense clusters of poles with closely spaced frequencies and mode shapes with similar wavelengths. Hence, this circumstance considerably hinders the identification of physical poles using standard stabilization diagrams. The imperfect independence between spans is typically due to the presence of a continuous deck over the simply supported girders, weak deck/asphalt connections and/or imperfect expansion joints. In this context, the coupling degree of spans manifests through global mode shapes and frequencies spanning between the limit cases of simply supported and continuous multi-span conditions. In this light, this work proposes a novel method to assist the clustering of modal poles extracted using OMA. The proposed method is based on the analytical modal solution to the free vibration problem of multi-span beams with weak rotational coupling between adjacent spans. The developed method is validated through the modal identification of a real-world in-operation multi-span reinforced-concrete girder bridge.
No abstract is provided for this article.
Railway bridge KW51 in Leuven, Belgium, has been monitored since October 2018 with the aim of validating various structural health monitoring techniques. The displacement and strain measurements on the structure show a nonlinear behavior, which is attributed to friction in the pot bearings. This paper describes and validates a methodology that allows the observed nonlinear behavior of the pot bearings to be modeled. This is important for understanding and reproducing the bridge behavior under combined train and thermal loading as in, e.g., virtual sensing applications. To this end, a previously developed detailed linear finite-element model of the bridge superstructure is augmented with nonlinear Bouc–Wen elements, representing the bearings. A comparison between the measured and predicted bearing displacements under train loading shows a significant improvement of the response prediction in comparison with the case where the bearings are modeled as roller supports, as assumed in the design. In addition, it is also shown that the model enables a qualitative description of the thermal bridge response.
