Damage characterization in waveguides with ultrasonic shear waves

Damage can be viewed as a continuum discontinuity. In order to identify and quantify damage, the present study investigates the dependence of reflection and transmission coefficients from a discontinuity in a waveguide using a finite element model. A parametric study of a fiber reinforced polymer laminate beam is presented with five different ratios of reduced cross-section with two different kinds of geometry: symmetric and asymmetric, in three discontinuity lengths. What is more, finite element results are compared with the corresponding results of a semi- analytical model based on the principle of reciprocity in elastodynamics. The analysis shows that: a) depending on the kind of discontinuity, the diagnostic potential of the used guided wave depends on the mode existence and on the magnitude of its wavelength in relation to the discontinuity extension, b) reflection and transmission coefficients can be used to identify and characterize damage both in symmetrical and asymmetrical damaged cross sections

Dynamic response of a damaging masonry wall

A nonlocal damage-plastic model is adopted to describe the nonlinear structural response of masonry structures. The model, based on a macromechanical approach, accounts for strength and stiffness degradation with hysteretic dissipation typically characterizing the masonry response, when it is subjected to horizontal loads. The stiffness recovery due to the crack closure, under cyclic loading, is also introduced by defining two different scalar damage variables for prevailing tensile and compressive states. To explore the effect of such nonlinear phenomena on the masonry structural response, the behavior of an unreinforced slender wall is investigated in the dynamic field. Special attention is devoted to the analysis of the wall frequency response curves (FRCs), obtained by imposing base harmonic accelerations with slowly time-variable frequency. These curves highlight the complexity of the dynamic phenomenon: due to the stiffness decay exhibited by the wall, a continuous variation of its natural frequencies occurs,which in turn modifies the resonance conditions. Finally, the wall response results strongly path-dependent and the characteristics of the wall restoring force lead to multi-valued FRCs

Effective filtering of modal curvatures for damage identification in beams

In this work, we investigate the effectiveness of a damage identification technique recently proposed in [1] and assess how it is affected by the number and position of the sensors used. Mode shapes and curvatures have been claimed to contain local information on damage and to be less sensitive to environmental variables than natural frequencies. It is known that notch-type damage produces a localized and sharp change in the curvature that unfortunately could be difficult to detect experimentally without the use of an adequate number of sensors. However, we have recently shown that even a coarse description of the modal curvature can still be employed to identify the damage, provided that it is used in combination with other modal quantities. Here, by exploiting the perturbative solution of the Euler-Bernoulli equation, we consider the inverse problem of damage localisation based on modal curvatures only and we ascertain the feasibility of their sole use for recostructing the damage shape. To do so, we set up a filtering procedure acting on modal curvatures which are expressed in a discrete form enabling further investigation on the effect of using a reduced number of measurement points. The sensitivity of the procedure to damage extension is further assessed

Out-of-plane dynamic response of a tuff masonry wall. Shaking table testing and numerical simulation

The out-of-plane dynamic response of a masonry element is investigated, both experimentally and numerically. The results of shaking table tests on a tuff masonry wall, subjected to harmonic acceleration histories, are presented. An isotropic nonlocal damage-plastic model, accounting for the masonry strength-stiffness degrading and hysteresis mechanisms, is introduced in a finite element procedure to numerically describe the masonry structural response. A simplified scheme is analysed, where the wall is completely restrained at the base and free at the top. The measured top displacement history is compared with that numerically evaluated, obtaining a satisfactory agreement. Moreover, the effects of the onset and evolution of the degrading mechanisms in the masonry wall are highlighted

Seismic Retrofit of Low-Rise Reinforced-Concrete Buildings: A Modified Displacement-Based Design Procedure

n/

Extraction of the beam elastic shape from uncertain FBG strain measurement points

Aim of the present paper is the analysis of the strain along the beam that is equipped with Glass Fibers Reinforced Polymers (GFRP) with an embedded set of optical Fiber Bragg Grating sensors (FBG), in the context of a project to equip with these new structural elements an Italian train bridge. Different problems are attacked, and namely: (i)during the production process [1] it is difficult to locate precisely the FBG along the reinforcement bar, therefore the following question appears: How can we associate the strain measurements to the points along the bar? Is it possible to create a signal analysis procedure such that this correspondence is found?(ii)the beam can be inflected and besides the strain at some points, we would like to recover the elastic shape of the deformed beam that is equipped with the reinforcement bars. Which signal processing do we use to determine the shape of the deformed beam in its inflection plane?(iii)if the beam is spatially inflected, in two orthogonal planes, is it possible to recover the beam spatial elastic shape? Object of the paper is to answer to these questions

Crack detection in beam-like structures by nonlinear harmonic identification

The dynamic behavior of beam-like structures with fatigue cracks forced by harmonic excitation is characterized by the appearance of sub and super-harmonics in the response even in presence of cracks with small depth. Since the amplitude of these harmonics depends on the position and the depth of the crack, an identification technique based on such a dependency can be pursued: the main advantage of this method relies on the use of different modes of the structure, each sensitive to the damage position in its peculiar way. In this study the identification method is detailed through numerical examples tested on structures of increasing complexity to evaluate the applicability of the method to engineering applications. The amount of data to obtain a unique solution and the optimal choice of the observed quantities are discussed. Finally, a robustness analysis is carried out for each test case to assess the influence of measuring noise on the damage identification

Investigation of the dynamic response and effect of soil properties of Arroyo Bracea II bridge in Madrid-Sevilla High-Speed railway line through experimental analyses

Faculty of Civil and Industrial Engineering of Sapienza University of Rome Italy, from Sunday 10 to Wednesday 13 September 2017In this contribution the authors include results and conclusions from an experimental and numerical analysis of a railway bridge belonging to the Madrid-Sevilla High-Speed railway line in Spain. This structure is monitored due to its short length and typology, which make it susceptible to experience high transverse vibration levels. During the in-situ tests the soil properties at the site were obtained. Also, the response of the structure under the circulation of railway convoys was measured at several points of the deck and at the abutments. From the experimental measurements the modal parameters of the bridge are identified. Finally the experimental results are compared to those provided by a finite element numerical model in the time and frequency domains. Conclusions are extracted regarding the structure performance and the adequacy of the numerical model implemented.Ministerio de Economía y Competitividad BIA2013-43085-PUniversitat Jaume I P1-1B2015-54Ministerio de Economía y Competitividad BIA2016-75042-C