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vol. 9 num. 1 lang. en<![CDATA[SciELO Logo]]>http://www.scielo.br/img/en/fbpelogp.gif
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<![CDATA[<b>Vibration analysis of stiffened plates using finite element method</b>]]>
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This paper presents the vibration analysis of stiffened plates, using both conventional and super finite element methods. Mindlin plate and Timoshenko beam theories are utilized so as to formulate the plate and stiffeners, respectively. Eccentricity of the stiffeners is considered and they are not limited to be placed on nodal lines. Therefore, any configuration of plate and stiffeners can be modeled. Numerical examples are proposed to study the accuracy and convergence characteristics of the super elements. Effects of various parameters such as the boundary conditions of the plate, along with orientation, eccentricity, dimensions and number of the stiffeners on free vibration characteristics of stiffened panels are studied.<![CDATA[<b>Dynamic response of low frequency Profiled Steel Sheet Dry Board with Concrete infill (PSSDBC) floor system under human walking load</b>]]>
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This paper investigates the dynamic response of a composite structural system known as Profiled Steel Sheet Dry Board with Concrete infill (PSSDBC) to evaluate its vibration serviceability under human walking load. For this point, thirteen (13) PSSDBC panels in the category of Low Frequency Floor (LFF) were developed using Finite Element Method (FEM). The natural frequencies and mode shapes of the studied panels were determined based on the developed finite element models. For more realistic evaluation on dynamic response of the panels, dynamic load models representing human walking load were considered based on their Fundamental Natural Frequency (FNF), and also time and space descriptions. The peak accelerations of the panels were determined and compared to the limiting value proposed by the standard code ISO 2631-2. Effects of changing thickness of the Profiled Steel Sheet (PSS), Dry Board (DB), screw spacing, grade of concrete, damping ratio, type of support, and floor span on the dynamic responses of the PSSDBC panels were assessed. Results demonstrated that although some factors reduced dynamic response of the PSSDBC system under human walking load, low frequency PSSDBC floor system could reach high vibration levels resulting in lack of comfortableness for users.<![CDATA[<b>Two efficient hybrid-trefftz elements for plate bending analysis</b>]]>
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This study is devoted to the analysis of the Reissner-Mindlin plate bending. In this paper, the hybrid-Trefftz strategy will be utilized. Two novel and efficient elements are formulated in details. They are a Triangular element (THT) and a quadrilateral element (QHT), which have 9 and 12 degrees of freedom, respectively. In this approach, two independent displacement fields are defined; one within the element and the other on the edges of the element. The internal field is selected in such a manner that the governing equation of thick plates could be satisfied. Boundary field is related to the nodal degree of freedoms by the boundary interpolation functions. To calculate these functions, the edges of the element are assumed to behave like a Timoshenko beam. The high accuracy and efficiency of the proposed elements and absence of the shear locking in these formulations are all proven, using various numerical tests.<![CDATA[<b>Determination of the reinforced concrete slabs ultimate load using finite element method and mathematical programming</b>]]>
http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1679-78252012000100004&lng=en&nrm=iso&tlng=en
In the present paper, the ultimate load of the reinforced concrete slabs [16] is determined using the finite element method and mathematical programming. The acting efforts and displacements in the slab are obtained by a perfect elasto-plastic analysis developed by finite element method. In the perfect elasto-plastic analysis the Newton-Raphson method [20] is used to solve the equilibrium equations at the global level of the structure. The relations of the plasticity theory [18] are resolved at local level. The return mapping problem in the perfect elasto-plastic analysis is formulated as a problem of mathematical programming [12]. The Feasible Arch Interior Points Algorithm proposed by Herskovits [8] is used as a return mapping algorithm in the perfect elasto-plastic analysis. The proposed algorithm uses Newton's method for solving nonlinear equations obtained from the Karush-Kuhn-Tucker conditions [11] of the mathematical programming problem. At the end of this paper, it is analyzed six reinforced concrete slabs and the results are compared with available ones in literature.<![CDATA[<b>A stress-displacement solution for a pressure tunnel with impermeable liner in elastic porous media</b>]]>
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Considering the effects of the changes of the pore water pressure around the opening, the construction sequence of the tunnel and the interaction between the liner and the surrounding geomaterial on the mechanical response of the tunnel and in conjunction with the analyses of the continuity and boundary conditions for the stress and displacement and hydraulic conditions, the elastic problem for a deep pressure tunnel with impermeable liner in a saturated elastic porous media that obeys Terzaghi's effective stress principle is investigated. The influences of the relative liner thickness and rigidity and the relative distance of the point under investigation to the tunnel axis on the stress-displacement fields for various combinations of the mechanical and geometric parameters are evaluated and discussed.<![CDATA[<b>Fuzzy logic for structural system control</b>]]>
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This paper provides some information and numerical tests that aims to investigate the use of a Fuzzy Controller applied to control systems. Some advantages are reported regarding the use of this controller, such as the characteristic ease of implementation due to its semantic feature in the statement of the control rules. On the other hand, it is also hypothesized that these systems have a lower performance loss when the system to be controlled is nonlinear or has time varying parameters. Numerical tests are performed using modal LQR optimal control and Fuzzy control of non-collocated systems with full state feedback in a two-dimensional structure. The paper proposes a way of designing a controller that may be a supervisory Fuzzy controller for a traditional controller or even a fuzzy controller independent from the traditional control, consisting on individual mode controllers. Some comments are drawn regarding the performance of these proposals in a number of arrangements.