No abstract is provided for this article.
Vibration-based monitoring (VBM) is widely applied for assessing the structural health of bridges, where tracking changes of modal characteristics is used for damage assessment. Natural frequencies are the most commonly employed modal characteristic for this purpose, but have the drawback that they are sensitive to temperature changes and not very sensitive to local stiffness variations. Recent case studies, primarily on steel railway bridges, have demonstrated that strain mode shapes offer a much higher sensitivity to local damage and are significantly less influenced by temperature. This study investigates the impact of temperature and solar irradiation on the natural frequencies and strain mode shapes of a post-tensioned concrete bridge used for vehicle traffic. For this purpose, a long-term monitoring campaign is performed, measuring operational dynamic strains and temperature. In agreement with existing case studies in literature, a significant impact of temperature and solar irradiation on the natural frequencies is observed. However, contrary to previous findings, also the strain mode shapes are found to be substantially temperature-dependent. This dependency is attributed to several factors: (1) the composite nature of the structure, where different materials have differing relationships between material properties and temperature, (2) the non-uniform temperature distribution caused by solar irradiation, and (3) the potential impact of changing support conditions and connections with varying temperatures. A finite element model was developed to capture these temperature-dependent effects, successfully replicating the observed temperature-induced changes in both natural frequencies and strain mode shapes. These findings suggest that composite bridges composed of diverse materials exhibit inherent variability in strain mode shapes, primarily due to their temperature dependency. For vibration-based damage detection, this implies that damage has to be sufficiently large to be detected through changes in strain mode shapes or neutral axis positions, if environmental variability is not accounted for.
The Zoned Finite Strip method, where one strip can have several different materials in the horizontal direction, has been extended for dynamic problems. Eigenfrequencies and eigenmodes are calculated e.g. in order to perform a response spectra analysis in the case of an earthquake loading. Besides the new dynamic capabilities, some improvements are proposed for the static case. Also some very efficient solution methods, specially for finite strip problems, are included and commented upon. The extensions have been applied to three different problems and the results are compared with analytical and numerical (finite element) methods. The examples show good agreement between the different methods.
Although the use of fibre reinforced concrete (FRC) for structural applications is continuously increasing, it is still limited with respect to its potentials.This can be mainly attributed to the lack of international building codes for FRC structural elements.This paper aims to contribute to the development of suitable design principles for shear in FRC elements by presenting the preliminary results of 6 full-scale pretensioned steel-fibre reinforced concrete members.The main investigated parameters are the amount of prestressing, the amount of shear reinforcement and the fibre dosage respectively.All specimens are subjected to a four-point bending test until failure.Traditional mechanical measurement devices are used in combination with advanced optical measurement systems (i.e.stereo-vision digital image correlation 3D DIC and Bragg grated optical fibres).Apart from the full-scale tests, a number of small-scale experimental investigations are performed to characterize the material properties.The experimentally determined results are compared to predictions using analytical models found in Eurocode 2 (EC2) and Model Code 2010 (MC2010).Based on the obtained full-field data from the DIC systems and the detailed deformation information obtained from the Bragg grated optical fibres, an assessment is made of the mechanical behaviour.
Statistical energy analysis (SEA) and related approaches to the high-frequency analysis of vibro-acoustic systems rely on a conceptual division of the system into subsystems that are assumed to carry a diffuse field and to be weakly coupled. Weak coupling in this context means that the exchange of energy between any two subsystems can be described in terms of their uncoupled free vibration modes. In this paper, a criterion is derived for assessing the coupling strength in the general case where the subsystems are rigidly coupled and/or via a deterministic linear dynamic component. First, the subsystems are taken to be deterministic and in a subsequent analysis they are taken to be diffuse subsystems in an SEA setting. The criterion is then 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 is shown to be identical to the γ criterion that has appeared in the literature for the coupling strength assessment of some special cases. The use of the criterion is illustrated with instructive validation examples involving two diffuse plate subsystems rigidly connected and/or via a deterministic beam, whose dynamic behaviour influences the coupling strength.
In Operational Modal Analysis (OMA) of large structures, it is often necessary to measure the Degrees Of Freedom (DOFs) of interest in different setups, which are processed separately, resulting in different modal parameter estimates for each of the setups. Subsequently, the DOFs that are common to the different setups are used to combine the different parts of the mode shapes, while the eigenfrequencies and damping ratios are averaged. This strategy is named the PoSER approach. If the number of setups is large, this approach is tiresome, especially if some modes of interest are not well excited and hence might be difficult to extract from the data. Therefore, there is an increasing interest towards processing all setups at once, which results in so-called ‘global’ modal parameter estimates. In this article, two strategies for achieving this goal, named the PoGER and PreGER approaches, are presented, both in the time and in the frequency domain. The PoSER as well as the global strategies are then used for the extraction of the modal parameters from data measured on the steel Luiz I arch bridge in Porto, Portugal, using both the SSI-cov/ref and the pLSCF system identification methods. From the comparison of the obtained results, it is concluded that the PoGER strategy is the most robust global approach.
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A three-dimensional (3D) finite element analysis on a newly developed type of coupler for glass-fibre-reinforced plastic (GRP) pipes under an internal pressure loading is presented. The stress distribution within the coupler is inhomogeneous with apparent stress concentrations located at the pipe and the coupler edges. Delamination and debonding are the main failure modes. Therefore, a fracture mechanical approach is preferred in the design of the coupler instead of a purely strength-based failure criterion evaluation. The strain-energy release rates evaluated at the critical delamination sites are used as a performance measure of the coupler. A comparative parametric study is carried out to allow for the dimensioning and shaping of the coupler as well as for the choice of an optimal stacking sequence.
A new efficient global optimization technique, named Coupled Local Minimizers (CLM), is presented in the paper. The CLM method uses a set of search points, initially spread over the search space. In each search point the function and derivative values are calculated and used to direct the search process. But instead of performing separate, independent searches from each of these points (i.e. multi-start local optimization), the set of optimizers are coupled during the search process in order to create interaction between them, which results in a cooperative search mechanism. The combination of a fast convergence—due to the derivative information that is used—with the capability of finding the global minimum — resulting from the parallel strategy — guarantees an efficient global optimization algorithm. The paper proposes an implementation based on the second-order Newton method in order to increase the convergence speed. The CLM method and its implementation are described extensively in the paper and are illustrated with a test function containing several local minima. The paper focusses on low-dimensional optimization problems only.
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No abstract is provided for this article.
No abstract is provided for this article.
