جستجوی مقالات مرتبط با کلیدواژه "moving load" در نشریات گروه "عمران"

Civil structures are always considered one of the most valuable properties of each country. Many factors can lead to local damages in different parts of structures during their operational life. These damages are reflected in the vibration responses of structures. This research aims to detect the existence and determine the location of damage in a truss bridge under a moving load using an artificial neural network and experimental wavelet transform. For this purpose, a two-dimensional truss bridge was built in the laboratory to investigate this research's objectives. Earlier experimental studies in damage detection were subjected to excitations such as impact loads and electrodynamic shakers. Since the appearance of damage effects in the vibration responses of the structure mainly depends on the applied location of the impact load, a moving load that crosses the entire length of the bridge can be used as input excitation to detect the presence and location of damages for which there is no available data. After measuring the vibration responses of the bridge, 17 time-domain features were extracted from the raw signals, which were used to detect the presence of damage. Although feature extraction is applied to raw signals, the signal processing stage was not eliminated for damage localization. By processing the response signals of the healthy and damaged state of the bridge using experimental wavelet transform, these signals were decomposed into different modes and 5 non-parametric damage-sensitive features such as Shannon and Tsallis entropies, Root Mean Square (RMS), Shape Factor and kurtosis which are all based on statistical parameters in addition to energy, were extracted. Finally, these damage-sensitive features were presented as input to the neural network whereas the state of the bridge (healthy or damaged) was considered as its target. The obtained results showed that the proposed method can effectively detect the presence and the location of the damage in the truss bridge.

In this paper, formulation of a recently proposed time-weighted residual method has been developed for the vibration analysis of Timoshenko beams under moving loads. Employing pre-integration relations as well as equilibrium equations, is the main idea of this method. In the first step of the proposed method, the time interval is subdivided into a number of sub-intervals and then the acceleration field in each sub-interval is defined as the combination of an unknown function and an exponential series with constant coefficients. Finally, the solution of the problem is estimated by the time-weighted residual method along with exact satisfaction of the initial and the boundary conditions at the two ends of the beam. Storing the information of solution at each time step on the exponential coefficients, is the most important advantage of this method, so that the solution is progressed in time without the need to discretize beams and only by using an appropriate recursive relation to update the exponential coefficients. In order to investigate the accuracy and efficiency of the proposed method, the results of solving three sample problems of constant and accelerated moving load on the beams with different boundary conditions, are compared with the results of finite element method. This comparison illustrates the speed and accuracy of the proposed method in estimating the internal shear forces and bending moments rather than those obtained by the finite element method.

In present study, dynamic analysis of thin circular plates under an orbiting load and mass by employing Boundary Characteristics Orthogonal Polynomials (BCOPs) would be explored. These polynomials would obviate the use of trigonometric or Bessel functions for the Rayleigh-Ritz method. BCOPs are widely utilized in plates with various geometries such as rectangular, circular, triangle and elliptic plates. The boundary conditions are applied to the first polynomial and the rests would be produced by the Gram-Schmidt process. In this regard, after verification of the accuracy and convergence rate of this method in evaluating the static response as well as the natural frequencies of the circular plates with simple and clamped boundary conditions, dynamic deflection of these plates excited by an orbiting load and mass. By introducing the vertical component of the orbiting load acceleration, the inertial effects of the moving load are investigated. The obtained results reveal the importance of the load inertia in dynamic response of the structure, especially near the resonant states.