This paper addresses two important worldwide environmental concerns: disposal of waste tyres and attenuation of trains induced vibration. To this end, use of the waste materials in construction of ...railway concrete slabs for reduction of train induced vibration is investigated in this research. For this purpose, rubber tyre particles with different dosages were used in the concrete mixtures of test specimens. Extensive laboratory tests were conducted on the rubberized concrete specimens to measure their compressive strength, density and damping of the specimens. The effect of rubberized slab track on attenuation of vibration propagated from slab track was investigated by numerical modeling using results of laboratory tests as the input data. The laboratory results obtained indicate that adding rubber particles to the railway slab causes up to 96% increase in damping ratio (for concrete with 10% rubber). Results of numerical analysis elucidates that the rubberized slab track causes up to 21% reduction of the train induced vibration. By compromising between compressive strength and damping of vibration, it is shown that the optimum amount of crumb rubber in the concrete of railway slabs is 2.5% by which the best performance of the railway slabs is obtained.
•This paper addresses two important environmental challenges in the world.•A method for recycling waste tyres and reducing railway vibration is developed.•Optimum amount of crumb rubber integrated into railway concrete slab is derived.•Environment-friendly solution for mitigation of train induced vibration is derived.
This work used free vibration tests based on impulse excitation technique and experimental modal analysis using an impact hammer and an accelerometer to assess the local and global effects of the ...hygrothermal ageing of GFRP specimens exposed to salt-spray environment at 35°C and 60°C over a period of 136 days. Through the change in elastic properties, fifteen natural frequencies and damping ratios, the effects of degradation are associated with reductions in elastic properties and natural frequencies and an increase in damping ratios. In turn, the increase in elastic properties and natural frequencies – associated with a reduction in damping ratios – is mainly attributed to the post-curing effect.
•Hygrothermal ageing of FRP angle members and coupons is reported.•Impulse excitation technique is adopted to monitor reduction of elastic properties.•Experimental modal analysis is used to study variations in natural frequencies and damping ratios.•Combined influence of material degradation and ageing is discussed.
This paper proposes a two-stage approach for damage assessment in beam-like structures using two-dimensional Isogeometric Analysis (IGA) and Finite Element Method (FEM) combined with optimization ...techniques. In the first stage, the Local Frequencies Change Ratio (LFCR) indicator and a newly developed damage indicator based on normalized Modal Strain Energy Indicator (nMSEDI) are introduced to locate effectively the potential damaged elements. In order to verify nMSEDI, different scenarios based on single and multiple damages are studied using numerical experiments. In the second stage, the Teaching-Learning-Based Optimization Algorithm (TLBO) is utilized and its performance is compared with that of Particle Swarm Optimization (PSO) and Bat Algorithm (BA). The three optimizations techniques are combined with IGA using nMSEDI as objective function. In addition, experimental vibration tests using laboratory steel been are conducted to validate the proposed technique. The obtained results clearly indicate that the proposed approach can be used to determine accurately and efficiently both damage location and severity in beam-like structures.
The article introduces a method for selecting the best clamping conditions to obtain vibration reduction during the milling of large-size workpieces. It is based on experimental modal analysis ...performed for a set of assumed, fixing conditions of a considered workpiece to identify frequency response functions (FRFs) for each tightening torque of the mounting screws. Simulated plots of periodically changing nominal cutting forces are then calculated. Subsequently, by multiplying FRF and spectra of cutting forces, a clamping selection function (CSF) is determined, and, thanks to this function, vibration root mean square (RMS) is calculated resulting in the clamping selection indicator (CSI) that indicates the best clamping of the workpiece. The effectiveness of the method was evidenced by assessing the RMS value of the vibration level observed in the time domain during the real-time face milling process of a large-sized exemplary item. The proposed approach may be useful for seeking the best conditions for fixing the workpiece on the table.
The durability and simplicity of the programming of meta-heuristic algorithms make them important in the optimization field. This paper presents a novel application for double cracks identification ...in Carbon Fiber Reinforced Polymer (CFRP) cantilever beams based on experimental and numerical analyses using enhanced optimization techniques. A new hybrid algorithm Particle Swarm Optimization and YUKI (PSO-YUKI) is proposed and combined with Radial Basis Functions (RBF) for solving fast inverse problems. The direct problem is based on the results of the dynamic experimental test of CFRP laminate, measuring the dynamics characteristics of a healthy beam, and the variation in the response corresponding to different scenarios of double cracks with different depths. The Finite Element Method (FEM) is used to simulate this vibrational behavior considering double cracks in different locations. The goal is creating an accurate damage identification method that has a high computational performance, based on the idea of building models that combines the vibrational responses issued from the experiments and simulations. The suggested method is tested based on collected data from numerical and experimental modal analyses in the case of undamaged and damaged CFRP laminates to demonstrate its accuracy and efficiency. The provided results show the robustness of PSO-YUKI compared with PSO for double cracks depth identification. The Matlab Code of PSO-YUKI can be found at https://github.com/Samir-Khatir/Hybrid-PSO-YUKI-.git.
This study develops an efficient method using input–output data on estimating non-parametric and then parametric frequency response functions (FRFs) associated with a dynamic system. Contrary to most ...existing FRF estimation methods that have been theoretically based on the steady-state or stationary responses, the proposed method uses the transient responses that are induced by simple, such as sinusoidal or two-exponential, excitations instead. Its numerical procedure for obtaining a non-parametric FRF is nothing more than solving a set of linear equations in which the unknown variables are individual components of the sought FRF. Furthermore, from the non-parametric FRF, its corresponding poles and residues are extracted through a procedure that involves a usage of the inverse discrete Fourier transform and the Prony-SS method; afterwards, a partial fraction FRF in terms of poles and residues can be achieved. Three numerical examples, including computer simulations and lab experiment, are provided to demonstrate the superior performance of the developed method.
•Report analytical formulae for ID of modal parameters in EMA.•Characterize the difference in ID of modal parameters between EMA and OMA.•Mode shape c.o.v. for EMA shares the same formula as that for ...OMA.•Provide the scientific basis for planning the single-input forced vibration test.
‘Uncertainty law’ aims at closed-form asymptotic formulas for the relationship between the identification uncertainties of modal properties (e.g., natural frequency, damping ratio) and test configuration (e.g., noise level, number and location of sensors, data duration). Existing developments focused on the case of unknown-input (ambient), where it has been found that identification uncertainty does not vanish even for noiseless instruments, essentially because the input is unknown. A natural question is then on how the uncertainty depends on test configuration when the input is known, not to mention how the configuration should be quantified. Motivated by these and related questions, this paper develops the uncertainty laws of modal parameters for well-separated modes with known single broadband input, e.g., vibration test with a single shaker as in experimental modal analysis. Asymptotic expressions for the posterior coefficient of variation of modal parameters are derived via the Fisher Information Matrix for long data and small damping scenarios. Assumptions and theory are validated using synthetic and field test data. Governing factors motivated by the theory are investigated, including the equivalent modal signal-to-noise ratio (for known input), the number of measured degrees of freedom, shaker location, and data duration. By virtue of the Cramér-Rao bound in classical statistics, the developed uncertainty laws represent the lower bound of identification uncertainty with known broadband input that can be achieved by any unbiased estimator. They provide a scientific basis for planning and managing identification uncertainties in vibration tests with known input.
The importance and role of a specific class of global transmissibility matrices (global TFs), here named response-based frequency response functions (R-FRFs), in the areas of the identification and ...continuous monitoring of structures, is discussed and expanded in the present paper. The R-FRFs, as specialized frequency response functions, have been recently introduced in the literature, and, as originally proved, they are able to inherently provide local poles related to the system under investigation, but, virtually, with a different set of boundary conditions; i.e. as if some of the original degrees of freedom, arbitrarily chosen by the analyst, were constrained to ground. In this paper, such a concept is extended, including mode shapes. Herein, we show that the R-FRFs are also able to provide local modes associated with the aforementioned local poles. In this regard, we provide a parametric model of the R-FRFs matrix, suitable for being tackled through frequency-domain estimators from the field of experimental and operational modal analysis, which let these additional modal parameters to be identified. Such a conceptual extension is carried out by both a theoretical and a numerical point of view. We process data sets from numerical and real-world experimental case studies and discuss the corresponding results. The estimated poles and modes are employed to detect structural modifications, in turn confirming the significance of response-based frequency response functions in the field of damage detection and structural health monitoring (SHM).
•Response-based FRFs (R-FRFs) as a tool for analyzing the system in a local sense.•R-FRF modal decomposition in terms of perturbated original system modal parameters.•Modes of the original structure when subjected to virtual boundary conditions.•Modal parameter estimation based on frequency-domain estimator from the OMA field.•Sensitivity of R-FRF modal parameters for enhanced damage localization.
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