1,720,974 research outputs found
Dynamic behavior of stay cables with rotational dampers
No full textVibration reduction in stay cables by means of viscous dampers is of great interest in cable damage prevention and serviceability of structural system supported by such cables. The paper presents a study on the effectiveness, as well as the limits, of rotational viscous dampers and springs inserted at the two ends of a bending-stiff taut cable; influence of rotational stiffness of the springs is also investigated. After a nondimensional expression of the equation of motion has been obtained, as in other cases of nonproportionally damped continuous structures, complex modal analysis is pursued, obtaining complex eigenvalues and eigenfunctions. Comparison with intermediate dampers, widely used in bridge engineering, is performed showing the range of nondimensional parameters for which the proposed approach is of interest. Finally, a numerical technique based on complex mode superposition is presented in order to evaluate time domain responses for transversal distributed excitation. As an example, the procedure is applied to a wind-exposed cable. © 2010 ASCE
Vibrations of inclined cables under skew wind
No full textA non-linear finite element model of inclined cables, i.e. cables with non-leveled supports, in the large displacement and deformation fields is proposed for computing the dynamic response to wind loads which blow in arbitrary direction. The initial equilibrium, assumed as the static configuration under self-weight and mean wind component, is defined by a continuous approach, following an iterative procedure which starts from the configuration under self-weight only. The proposed formulation, which accounts for longitudinal inertia forces, allows to spot the circumstances when the simplified small-sag approach, adopting longitudinal mode condensation, becomes too crude. Numerical simulations have been performed employing the Proper Orthogonal Decomposition to lower the computational effort. © 2011 Elsevier Ltd
Statics of elastic cables under 3D point forces
No full textThe catenary problem for elastic cables is extended to the case of uniformly distributed loads and point forces however oriented in space. The equilibrium equation is written in vector form and its solution, i.e. the deformed shape of the elastic cable, is obtained in closed form for the cases of uniformly distributed load, one point force and many point forces. The formulation is suitable to solve straightforwardly cable structure problems, as shown in the numerical applications. © 2011 Elsevier Ltd. All rights reserved
Dynamics of shallow cables under turbulent wind: A nonlinear finite element approach
No full textIn classic cable theory, vibrations are usually analyzed by writing the equations of motion in the neighborhood of the initial equilibrium configuration. Furthermore, a fundamental difference exists between out-of-plane motions, which basically corresponds to the linear behavior of a taut string and in-plane motion, where self-weight determines a sagged initial profile. This work makes use of a continuous approach to establish the initial shape of the cable when it is subjected to wind or fluid flow arbitrarily directed and employed a novel nonlinear finite element technique in order to investigate the dynamics present around the initial equilibrium shape of the cable. Stochastic solutions in the frequency domain are derived for a wind-exposed cable after linearization of the problem. By applying the proper orthogonal decomposition (POD) technique with the aim of reducing computational effort, an approach to simulate modal wind forces is proposed and applied to the nonlinear equations of motion. © 2011 World Scientific Publishing Company
Crack identification in a beam by measure of the response to white noise
No full textThe aim of this paper is to inspect the vibrational response of a beam with an edge non-propagating crack by means of stochastic analysis, in order to detect the presence and the location of structural damage. The non- linear behavior of the beam due to the opening and closing of the crack is fully exploited. The non-linearity measure is based on the response evaluation of the beam subjected to a white noise process. Both numerical and experimental investigations regarding a cantilever beam with a crack are reported in the paper
Experimental tests and seismic performance of a concrete bridge
No full textIn this paper the experimental tests and the evaluation of the seismic behaviour of the seven simply supported spans concrete bridge crossing the Anapo River (Siracusa, Italy) is proposed. The bridge was not designed according to a seismic code and now is affected by visible damages. An experimental investigation was made in order to evaluate the reliability of the bridge regarding the recent seismic Italian code. The materials were characterized by means of tests on specimens extracted in different locations of the structure. Dynamic tests were done in order to update the finite element model
Numerical and experimental verification of a technique for locating a fatigue crack on beams vibrating under Gaussian excitation
No full textThe stationary vibrations of a beam excited by Gaussian noise are strongly affected by the presence of a fatigue crack. Indeed, as soon as the crack arises the system response becomes non-linear due to crack breathing and a non-Gaussian behaviour is encountered. The paper presents both numerical and experimental investigations in order to assess the capability of the non-Gaussianity measures to detect crack presence and position. Monte Carlo method is applied to evaluate in time domain the higher order statistics of a cantilever beam modelled by finite elements. The skewness coefficient of the rotational degrees of freedom appears the most suitable quantity for identification purpose being very sensitive to the non-linear behaviour of the cracked beam
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