Application of industrial by-products as mineral admixtures for self-compacting concrete

Upotreba otpadnih materijala kao mineralnih dodataka samozbijajućem betonu može pridonijeti rješavanju problema njihovog odlaganja, ali je potrebno utvrditi njihovu djelotvornost. Ispitan utjecaj elektrofiltarskog pepela, mljevenih otpadnih opekarskih elemenata – crjepova, flotacijske jalovine i silicijske prašine na konzistenciju betona i njihove tlačne čvrstoće, vlačnu čvrstoću pri savijanju i vlačnu čvrstoću pri cijepanju. Dobiveni rezultati ispitivanja mješavina samozbijajućeg betona su uspoređeni s mješavinom konvencionalnog betona.Although the use of waste materials as mineral admixtures for self-compacting concrete can contribute to solving the problem of their disposal, the effect of such use should be further explored. The influence of fly ash, powdered waste brick elements - roof tiles, flotation tailing and silica fume, on the consistency, compressive strength, bending tensile strength, and tensile splitting strength of concrete, is studied. Self-compacting concrete mixtures test results are compared to a common concrete mixture

A novel approach for vibration analysis of fractional viscoelastic beams with attached masses and base excitation

The Galerkin method is widely applied for finding approximate solutions to vibration problems of beam and plate structures and for estimating their dynamic behavior. Most studies employ the Galerkin method in the analysis of the undamped systems, or for simple structure models with viscous damping. In this paper, a novel approach of using the Galerkin method and Fourier transform to find the solution to the problem of vibration of fractionally damped beams with an arbitrary number of attached concentrated masses and base excitation is presented. The considered approach is novel and it lends itself to determination of the impulse response of the beam and leads to the solution of the system of coupled fractional order differential equations. The proposed approximate solution is validated against the exact solution for a special case with only one tip mass attached, as well as against the Finite Element Method Solution for a special case with classical viscous damping model. Numerical analysis is also given, including the examples of vibration analysis of viscoelastic beams with different fractional derivative orders, retardation times, and the number, weight and position of the attached masses

PREDLOG NOVOG NUMERIČKOG MODELA ZA ODREĐIVANJE ČVRSTOĆE BETONA OJAČANOG VLAKNIMA

An alternative numerical model for fiber reinforced concrete (FRC) compressive and bending tensile strength determination is presented in this paper. Fibers are modeled explicitly by using the Extended Finite Element Method (XFEM). An alternative method for modeling the fiber-matrix interaction, without the need for additional subroutine definition, is proposed. The presented numerical model was evaluated by experimental tests and results are in good agreement. The model was developed for Simulia ABAQUS software, but the proposed modeling procedure is generally applicable. In the end, some possible model improvements and suggested applications are included.U ovom radu je prikazan alternativan numerički model za određivanje čvrstoće betona ojačanog vlaknima na pritisak i na zatezanje savijanjem. Vlakna su modelirana diskretno, koristeći Prošireni Metod Konačnih Elemenata (Extended Finite Element Method – XFEM). Predložen je i  novi način modeliranja interakcije između vlakana i betonske matrice, bez potrebe za definisanjem dodatnih podrutina.Predloženi numerički model proveren je prema ekxperimentalnim ispitivanjima i rezultati se slažu u zadovoljavajućim granicama. Model je razvijen za rad u Simulia Abakus softveru (Simulia ABAQUS), ali je prikazana procedura opšte primenljiva. Na kraju su izložena i moguća unapređenja modela i predlozi njegove primene

Vibration of a coupled fractional viscoelastic multi-nanobeam systems

This paper shows the transverse vibration analysis of complex multiple coupled nanobeams system. Observed system is composed of an arbitrary number of aligned nanobeam structures embedded in viscoelastic medium where damping features of nanobeams and viscoelastic medium are represented by the fractional viscoelastic models while small-scale effects are considered using the Eringen’s nonlocal elasticity. In addition, non-homogeneities of the system such as different nanobeams cross-sections or density are observed within the paper. Governing equations are derived using using the d’Alembert’s principle, differential form of nonlocal stress relation and local stress-strain viscoelastic constitutive equation of fractional Kelvin-Voigt type. Semi-analyitical solutions for the transient response of simply supported nanobeams in the system are obtained using the separation of variables method, Laplace and Mellin-Fourier integral transforms, residue theory and modal expansion method. The problem of decoupling the governing equations of a non-homogenous system is solved by adopting the methodology from the literature. Several numerical examples are given to show the effects of different physical parameters on the transient response of such a system. Presented dynamic analysis and results could be used in future theoretical studies with additional physical effects included into the model. There is also a potential for use of this type of analysis in design procedures of modern nanodevices for calculation of their dynamic behavior that is much faster compared to atomistic based models

Nonlinear energy harvester with coupled Duffing oscillators

Structural vibrations are very common in aerospace and mechanical engineering systems, where dynamic analysis of modern aerospace structures and industrial machines has become an indispensable step in their design. Suppression of unwanted vibrations and their exploitation for energy harvesting at the same time would be the most desirable scenario. The dynamical system presented in this communication is based on a discrete model of energy harvesting device realized in such a manner as to achieve both vibration suppression and harvesting of vibration energy by introducing the nonlinear energy sink concept. The mechanical model is formed as a two-degree of freedom nonlinear oscillator with an oscillating magnet and harmonic base excitation. The corresponding mathematical model is based on the system of nonlinear nonhomogeneous Duffing type differential equations. To explore complex dynamical behaviour of the presented model, periodic solutions and their bifurcations are found by using the incremental harmonic balance (IHB) and continuation methods. For the detection of unstable periodic orbits, the Floquet theory is applied and an interesting harmonic response of the presented nonlinear dynamical model is detected. The main advantage of the presented approach is its ability to obtain approximated periodic responses in terms of Fourier series and estimate the voltage output of an energy harvester for a system with strong nonlinearity. The accuracy of the presented methodology is verified by comparing the results obtained in this work with those obtained by a standard numerical integration method and results from the literature. Numerical examples show the effects of different physical parameters on amplitude-frequency, response amplitude - base amplitude and time response curves, where a qualitative change is explored and studied in detail. Presented theoretical results demonstrate that the proposed system has advanced performance in both system requirements - vibration suppression, and energy harvesting

Non-reciprocal wave propagation in time-modulated elastic lattices with inerters

Non-reciprocal wave propagation in acoustic and elastic media has received much atten- tion of researchers in recent years. This phenomenon can be achieved by breaking the reci- procity through space- and/or time-dependent constitutive material properties, which is an important step in overcoming the limitations of conventional acoustic- and phononic-like mechanical lattices. A special class of mechanical metamaterials with non-reciprocal wave transmission are latices with time-modulated mass and stiffness properties. Here, we in- vestigate the non-reciprocity in elastic locally resonant and phononic-like one-dimensional lattices with inerter elements where mass and stiffness properties are simultaneously modulated through inerters and springs as harmonic functions of time. By considering the Bloch theorem and Fourier expansions, the frequency-band structures are determined for each configuration while asymmetric band gaps are found by using the weighting and threshold method. The reduction in frequency due to introduced inerters was observed in both phononic and locally resonant metamaterials. Dynamic analysis of finite-length lat- tices by the finite difference method revealed a uni-directional wave propagation. Special attention is given to phononic-like lattice based on a discrete-continuous system of multi- ple coupled beams. Moreover, the existence of edge modes in the discrete phononic lattice is confirmed through the bulk-edge correspondence and their time evolution quantified by the topologically invariant Chern number. The proposed methodology used to inves- tigate non-reciprocal wave transmission in one-dimensional inerter-based lattices can be extended to study more complex two-dimensional lattices