Computational Methods in Engineering

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A solution technique for the dynamic analysis of asymmetric base-isolated buildings, subject to earthquake ground motion, is presented. To develop the formulation, a yield surface as a function of both shear force and torsion moment of the sliding surface with rigid perfectly plastic behavior is constituted. To achieve the objective, the yield stress is defined by the friction coefficient through a simple relation. Having introduced the mathematical model of the yield surface, the simple conditions of being at the onset of sliding and nonsliding phases of motion are given. Based on the elaborated model, the earthquake dynamic analysis of a 3-D structure is performed. The results are in good agreement with those obtained by the finite-element modeling of the surface.

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A frequency domain dynamic analysis is needed to obtain the response of structures constructed on a system of base isolators on flexible soil when subjected to earthquake ground motion. In such systems, the lateral stiffness of the base isolators is so small, compared to the structural stiffness, that in an earthquake attack the fundamental vibration mode dominates the response. With this in mind, a simple equivalent model is introduced for the assembled structure and its flexible isolators. Next, this simple model is modified to include the effect of soil flexibility. This final model is believed to be appropriate for the frequency domain analysis of the whole system. Frequency independent dynamic characteristics of the model are determined and several response spectra pairs are prepared for both the exact and developed models. The results are in good agreement while the computational efforts for the simplified model is less.

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This paper may be regarded as a new numerical method for the analysis of triangular thin plates using the natural area coordinates. Previous studies on the solution of triangular plates with different boundary conditions are mostly based on the Rayleigh-Ritz principle which is performed in the Cartesian coordinates. Consequently, manipulation of the geometry and numerical calculation of the integrals are time consuming and tedious. In this paper a new approach is developed to analyze triangular plates by the Ritz method, using interpolation functions in the area coordinates. The geometry is presented in a natural way by mapping a parent triangle and the integrals are evaluated analytically. In this approach, the convergence is always assured due to the completeness of interpolating polynomials. Several examples are presented and the results are compared with other available data.

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In the Present study, attempt will be made to propose a new method for prediction of long-term essential creep of concrete utilizing some short-term creep tests under high temperature. To do so, regarding the similarities between essential creep of concrete and creep in viscoelastic materials, the time–temperature equivalence relation in viscoelastic materials is evaluated for concrete. This relation states that experimental curves of creep at different temperatures fit into a single curve when shifted along the axis of logaritmic time. To develop the model, an equation was first developed taking into account the effect of temperature and the maturity of concrete. Then, an appropriate method was proposed for transmission of the creep curve of concrete under a specific temperature to fit in the creep curve of the same concrete under a temperature. The proposed model was verified using existing experimental data which very good agreement was observed.

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Based on classical plate theory, standard and spectral finite element methods are extended for vibration and dynamic stability of axially moving thin plates subjected to in-plane forces. The formulation of the standard method earned through Hamilton’s principle is independent of element type. But for solving numerical examples, an isoparametric quadrilateral element is developed using Lagrange interpolation functions. The spectral method is, in fact, the solution of motion equation for an axially moving plate. Although this method has some limitations concerning boundary condition of plate and in-plane forces, it leads to an exact solution of free vibration and stability of plates travelling on parallel rollers. The method can be used as a benchmark of accuracy of other numerical methods.

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