1,720,987 research outputs found
Influence of the objective function in the dynamic model updating of girder bridge structures
No full textIn the context of model updating of bridge structures, dynamic approaches are currently dominant. This is mainly due to the opportunity of performing dynamic tests under environmental and traffic loadings, without putting the bridges out of service. Several techniques have been proposed in the literature to control and address the relevant model updating workflow. These methods typically consider the structural frequencies, or a combination of frequencies with vibration modes. Dissipative properties are, on the contrary, more rarely considered in updating procedures, given their strong dependence on the amplitude of the vibrations and on the type of forcing load. In this work, six ruling objective functions are considered for the dynamic model updating of girder bridge structures. The first one, taken from the literature, is a widely used function based on discrepancies among numerical and experimental frequencies. Two additional functions, also derived from the existing literature, are subsequently considered: one focuses on vibration modes, utilizing the Modal Assurance Criterion (MAC), and the other incorporates both structural frequencies and mode shapes, deploying the Modal Flexibility Matrix (MFM). Three novel objective functions are introduced, which are adaptations of the previously mentioned ones, with alternative applications of MAC and MFM. These six functions are analyzed and discussed through two comprehensive experimental case studies, in which the relative weights of the specific function terms are also investigated. A quantitative selection criterion is proposed and examined in order to choose the most suitable objective function based on identifiability. The method implementation, leveraging second-order derivatives, is executed via a finite difference scheme
A pseudo-modal structural damage index based on orthogonal empirical mode decomposition
No full textA structural damage identification technique hinged on the combination of orthogonal empirical mode decomposition and modal analysis is proposed. The output-only technique is based on the comparison between pre- and post-damage free structural vibrations signals. The latter are either kinematic (displacements, velocities or accelerations) or deformation measures (strains or curvatures). The response data are decomposed by means of the orthogonal empirical mode decomposition to derive a finite set of orthogonal intrinsic mode functions; the latter are used as a multi-frequency and data-driven basis to build pseudo-modal shapes. A new damage index, the so-called pseudo-mode index, is introduced to compare the response obtained for the two states of the structural system and detect potential damages. The performance of the devised index in detecting a localised damage is shown through numerical and experimental tests on two structural models, namely a 4-degrees-of-freedom system and a two-hinged parabolic arch
Dynamic damage identification using complex mode shapes
Full text linkDamage, be it a material or a geometric degradation, modifies some features of the response foreseen by the original structural design. These variations, once the dependence on the damage causing them is established, can be used for
identification purposes. In the literature, vibration-based approaches usually compare some responses of linear elastic structures with dissipative properties that are assumed proportional to the mass and stiffness measures. However, such an assumption is reasonable for new, undamaged structures, but can be unreliable in existing, potentially damaged structures, particularly for damages localised in narrow areas. The eigenmodes of a proportionally damped system can be reduced to the real ones of the relevant ideal undamped system. On the other hand, non-proportional damping exhibits complex eigenmodes that cannot be reduced to those of the ideal, or of the proportionally damped, structure. Thus, we may assume the complexity of the eigenmodes as a measure of nonproportional damping, hence of damage. On this basis, some contributions in the literature verified the relationship among presence of damage and amount of complexity. Here, we propose a perturbation approach and an objective function able to identify presence, location and amplitude of localised damages,intended as sources of non-proportionality in viscously damped linear systems. A prototype naturally discrete structure with four degrees-of-freedom is chosen to test and show capability and accuracy of the proposed method
Finite element modeling of masonry elements reinforced with the CAM system
No full textSince most of the historical building heritage of many countries consists of masonry, such structures are of great interest in civil engineering. Unfortunately, the intrinsic chaotic nature of the masonry material results in poor tensile strength and poor ductility, from the mechanical point of view, and great modeling difficulties, from the engineering standpoint. Moreover, due to seismic events, human interventions and natural aging, masonry structures require the adoption of effective solutions aimed at the conservation, recovery, or preservation. Among the various techniques already available in the literature, this work focuses on the CAM® System. The CAM system is analyzed through a finite element macro-modeling approach, involving nonlinear constitutive laws. The proposed model is an enhancement of a formulation already available in the literature for unreinforced elements: masonry elements consider both plastic and damage effects and are based on a three-dimensional description of the stress–strain relationships, whereas the reinforcing tie ribbons (stainless-steel stripes) are discreetly modeled with truss elements, endowed with a tension-only bilinear constitutive law. In this computational framework, the main novelty regards the introduction of two new control parameters, able to sharply reduce the numerical instabilities revealed during some preliminary sensitivity studies. The outcomes given by the proposed model are also compared with the results gathered with experimental tests and other procedures: from the comparison, significant findings are collected from the perspective of structural modeling and design
Measured properties of structural damping in railway bridges
No full textDissipative properties of a structural system are difficult to be characterized in real structure. Nevertheless, damping features may be dominant in several operating conditions of railway bridges influencing fatigue life or passenger comfort during train passage. Observations treating real data acquired in operational condition on steel and concrete railway bridges belonging to the Italian network permits to highlight dissipative sources and features. Consequently, linearized modal damping ratios are evaluated through a recursive process on the acceleration signals acquired before, during and after train passages and/or in environmental conditions. Stochastic Subspace Identification has been used to identify state-space dynamical models able to reproduce the vibrations. Through these models, characterized by an increasing number of state-space variables, it is possible to extract modal damping ratios. A mechanical interpretation of damping characteristics is pursued through the evaluation of the differences with respect to a classical Rayleigh proportional damping matrix of the viscous matrix belonging to the identified state-space models determined through the system spectral features. A non-proportional damping index is presented as a basis to determine the influence of different sources of non-proportionality in the damping matrix (as the ballast layer under the track) and to justify the high value of damping observed in specific experimental campaigns
Dynamic testing and modeling of span interaction in high-speed railway girder bridges
No full textThis paper presents the results of an extensive experimental campaign conducted on high-speed railway girder bridges along the Rome-Florence railway line. The campaign includes material characterization and in-situ dynamic tests, incorporating vibration signals from both ambient-induced activities and train passages. The study focuses on the modeling and simulation procedures necessary for analyzing existing railway girder bridges, considering the dynamic interaction between adjacent simple supported spans. The degree of coupling caused by railroad equipment can lead to interaction phenomena, such as vibrations corresponding to mode shapes encompassing multiple spans, observed along the bridge. A multilevel modeling strategy is proposed, starting with a single span to identify the most accurate and computationally efficient approaches (frame-based, shell-based, or mixed). Subsequently, full-scale and reduced-order models of the entire structures are developed, considering the connections between rails, superstructure, and piers, to study the interaction between adjacent spans. Three case studies are presented to demonstrate the general validity of the proposed approaches, comparing the numerical results with experimental outcomes obtained from the in-situ tests
Optimal sensors placement in dynamic damage detection of beams using a statistical approach
Full text linkStructural monitoring plays a central role in civil engineering; in particular, optimal sensor positioning is essential for correct monitoring both in terms of usable data and for optimizing the cost of the setup sensors. In this context, we focus our attention on the identification of the dynamic response of beam-like structures with uncertain damages. In particular, the non-localized damage is described using a Gaussian distributed random damage parameter. Furthermore, a procedure for selecting an optimal number of sensor placements has been presented based on the comparison among the probability of damage occurrence and the probability to detect the damage, where the former can be evaluated from the known distribution of the random parameter, whereas the latter is evaluated exploiting the closed-form asymptotic solution provided by a perturbation approach. The presented case study shows the capability and reliability of the proposed procedure for detecting the minimum number of sensors such that the monitoring accuracy (estimated by an error function measuring the differences among the two probabilities) is not greater than a control small value
Effect of local stiffeners and warping constraints on the buckling of symmetric open thin-walled beams with high warping stiffness
Full text linkLocal stiffeners affect the behaviour of thin-walled beams (TWBs). An in-house code based on a one-dimensional model proved effective in several instances of compressive buckling of TWBs but gave counterintuitive results for locally stiffened
TWBs. To clarify the matter, we investigated TWBs with multi-symmetric double I cross-section, widely used in practical applications where high bending stiffness is required. Several samples were manufactured and stiffened on purpose, closing them over a small portion of the axis at different places. The samples were tested with end constraints accounting
for various warping conditions. The experimental and numerical outputs from a commercial FEM code gave a key to overcome the unexpected results by the in-house code, paving the way for further studies
Structural meshes from photographic and laser campaigns: a contribution on retopology-based pipelines
No full textAbstract This contribution proposes workflows that allow the transition from photographic and laser surveys to point clouds and geometric meshes designed for structural analysis. The process is complex and, even today, is typically handled using uncontrolled methods. These methods are often unregulated, relying on the transfer of data across multiple software tools. Such unsupervised workflows frequently jeopardize the accuracy and reliability of the final outcomes. Two experimental tests, a slab of concrete and a small-scale frame structure of steel, are reported in this paper to show the provided pipelines and check the relevant performances through state-of-the-art software. The proposed comparison between the pipelines serves to highlight key considerations for effectively managing the transformation to develop an accurate digital twin of the specified structure. Retopologization and interoperability with BIM environments are also discussed
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