Resumo em Inglês:

In this paper, nonlinear behavior analysis of an asymmetrically laminated composite beam (LCB) on nonlinear foundation under axial and in-plane thermal loading is considered. To solve the obtained governing equation, a novel method based on Laplace transform is used. The resulted approximate analytical solution allows us the parametric study of different parameters which influence the nonlinear behavior of the system. The numerical results illustrate that proposed technique yields a very rapid convergence of the solution as well as low computational effort. The accuracy of the proposed method is verified by those available in literatures.

Resumo em Inglês:

A simple efficient algorithm based on compressive diagonal strength of unreinforced masonry walls is presented to determine capacity curve of unreinforced masonry building. The compressive strength is calculated based on a new close form solution. The new close form solution is determined based on predicted results using interface elements for modeling of mortar joints. Finite element method with two-noded linear elements is used for analyses. Different masonry structures, including low- and high-rise unreinforced masonry buildings, are analyzed using the new closed-form solution and the presented algorithm. A comparison of results of the present work with experimental data and other methods similar to the discrete element method show proper accuracy of the analyses in the present work. Consequently, the closed form solution with proposed algorithm can be used to satisfactorily analyze unreinforced masonry structures to predict the ultimate base shear force and the pushover curve. Hence, practicing engineers can determine the behavior of an URM building and its performance level with proper accuracy under seismic excitation using concepts described in the present work.

Resumo em Inglês:

A general symplectic method for the random response analysis of infinitely periodic structures subjected to stationary/non-stationary random excitations is developed using symplectic mathematics in conjunction with variable separation and the pseudo-excitation method (PEM). Starting from the equation of motion for a single loaded substructure, symplectic analysis is firstly used to eliminate the dependent degrees of the freedom through condensation. A Fourier expansion of the condensed equation of motion is then applied to separate the variables of time and wave number, thus enabling the necessary recurrence scheme to be developed. The random response is finally determined by implementing PEM. The proposed method is justified by comparison with results available in the literature and is then applied to a more complicated time-dependent coupled system.

Resumo em Inglês:

This paper presents a numerical study devoted to the evaluation of the possibility of monitoring and controlling the dynamic behavior of a rotating machine with a cracked shaft by using an Electro-Magnetic Actuator (EMA). The EMA is located at the mid-span of the rotor to provide active control. The opening and closure (breathing) of the crack is determined by the stress field over its cross section resulting from the dynamic bending moment. The system is nonlinear due to the fact that the crack parameters must be determined for each time step and the EMA introduces forces that are inversely proportional to the square of the gap value between the stator and the rotor. The model developed takes into account the behavior of the crack and the in uence of the EMA. Simulations were carried out to access the possibility of controlling the breathing mechanism. The results obtained demonstrate the possibility of using the EMA in order to keep the crack closed along the rotation of the rotor, thus forming a self-healing scheme for the cracked rotor.

Resumo em Inglês:

In this paper we present an experimental study of a three dimensional physical model of a three-floor structure subjected to forced vibrations by imposing displacements in its support. The aim of this work is to analyze the behavior of the building when a dynamic vibration absorber (DVA) is acting. An analytic simplified analysis and a numerical study are developed to obtain the natural frequencies of the structure. Experiments are carried out in a vibrating table. The frequency range to be experimentally analyzed is determined by the first natural frequency of the structure for which the DVA damping effects are verified. The equipment capabilities, i.e. the frequencies, amplitudes and admissible load, limit the analyses. Nevertheless, satisfactory results are obtained for the study of the first mode of vibration. The effect of different amplitudes of the imposed support motion is also analyzed. In addition, the damping effect of the DVA device is evaluated upon varying its mass and its location in the structure. The characteristic curves in the frequency domain are obtained computing the Fast Fourier Transformation (FFT) of the acceleration history registered with piezoelectric accelerometers at different checkpoints for the cases analyzed.

Resumo em Inglês:

This paper proposes a strategy to achieve robust optimization of structures against high-cycle fatigue when a potentially large number of uncertain load cases are considered. The strategy is heavily based on a convexity property of some of the most commonly used high-cycle design criteria. The convexity property is rigorously proven for the Crossland fatigue criterion. The proof uses a perturbation technique and involves the principal stress components and analytical expressions for the applicable fatigue criteria. The multiplicity of load cases is treated using load ratios which are bounded but are otherwise free to vary within certain limits. The strategy is applied to a notched plate subject to traditional normal and shear loadings that possess uncertain or unspecified components.