Abstract in English:Buckling of beams made of functionally graded materials (FGM) under thermomechanical loading is analyzed herein. Properties of the constituents are considered to be functions of temperature and thickness coordinate. The derivation of the equations is based on the Timoshenko beam theory, where the effect of shear is included. It is assumed that the mechanical and thermal nonhomogeneous properties of beam vary smoothly by distribution of the power law index across the thickness of the beam. The equilibrium and stability equations for an FGM beam are derived and the existence of bifurcation buckling is examined. The beam is assumed under three types of thermal loadings; namely, the uniform temperature rise, heat conduction across the thickness, and linear distribution across the thickness. Various types of boundary conditions are assumed for the beam with combination of roller, clamped, and simply-supported edges. In each case of boundary conditions and loading, closed form solutions for the critical buckling temperature of the beam is presented. The results are compared with the isotropic homogeneous beams, that are reported in the literature, by reducing the results of the functionally graded beam to the isotropic homogeneous beam.
Abstract in English:Concrete multicell box-girder bridges are a common choice among the designers for various ranges of bridges. In order to provide safer and greater speed of traffic, the roadway is built as straight as possible. The use of skewed bridges has increased considerably in the recent years for roadway. The skewed bridges have quite different mechanical behavior from the straight bridges, although for skew angles less than 20 degrees, it is reasonably safe to ignore the effect of skew angles and analyze that at the straight bridge. In this study, in developing an analytical solution, an extensive parametric study was carried out to determine the maximum positive and negative stress distribution factors and to calculate the maximum distribution factor of deflection along the mid-span of skewed multicell box-girder bridges. A total of 240 representative bridges numerical models were selected and analyzed using SAP2000 finite element software. It was found that the span length, number of boxes, number of lanes and skew angles significantly affected the distribution factors of stress and deflection. Finally, several equations were proposed for stress and deflection distribution factors of multicell box-girder bridges for the application of American Association of State Highway and Transportation officials load and resistance factor design live loads.
Abstract in English:A procedure involving spectral Galerkin and integral transformation methods has been developed and applied to treat the problem of the dynamic deflections of beam structure resting on bi-parametric elastic subgrade and subjected to travelling loads. The case of the response to moving constant loads of this slender member is first investigated and a closed form solution in series form describing the motion of the beam while under the actions of the travelling load is obtained. The response under a variable magnitude moving load with constant velocity is finally treated and the effects of prestressed, foundation stiffness, shear modulus and damping coefficients are investigated. Results in plotted curves indicate that these structural parameters produce significant effects on the dynamic stability of the load-beam system. Conditions under which the beam-load system may experience resonance phenomenon are also established some of these findings are quite useful in practical applications.
Abstract in English:This paper focuses on a metamodel-based design optimization algorithm. The intention is to improve its computational cost and convergence rate. Metamodel-based optimization method introduced here, provides the necessary means to reduce the computational cost and convergence rate of the optimization through a surrogate. This algorithm is a combination of a high quality approximation technique called Inverse Distance Weighting and a meta-heuristic algorithm called Harmony Search. The outcome is then polished by a semi-tabu search algorithm. This algorithm adopts a filtering system and determines solution vectors where exact simulation should be applied. The performance of the algorithm is evaluated by standard truss design problems and there has been a significant decrease in the computational effort and improvement of convergence rate.
Abstract in English:The dynamic response to moving masses of rectangular plates with general classical boundary conditions and resting on variable Winkler elastic foundation is investigated in this work. The governing fourth order partial differential equation is solved using a technique based on separation of variables, the modified method of Struble and the integral transformations. Numerical results in plotted curves are then presented. The results show that as the value of the rotatory inertia correction factor Ro increases, the response amplitudes of the plate decrease and that, for fixed value of Ro, the displacements of the plate decrease as the foundation modulus Fo increases for the variants of the classical boundary conditions considered. The results also show that for fixed Ro and Fo, the transverse deflections of the rectangular plates under the actions of moving masses are higher than those when only the force effects of the moving load are considered. For the rectangular plate, for the same natural frequency, the critical speed for moving mass problem is smaller than that of the moving force problem for all variants of classical boundary conditions, that is, resonance is reached earlier in moving mass problem than in moving force problem. When Fo and Ro increase, the critical speed increases, hence, risk is reduced.
Abstract in English:In this paper, a new 12-node triangular element is developed for the analysis of composite plates. Moreover, the stress-strain relations of laminated bending plates, along with the characteristics of composite and piezoelectric materials have also been investigated. Following this, a finite element formulation for smart composite bending plates is proposed. The capability of the suggested element in analyzing both composite plates and smart ones is studied via numerical examples. These analyses demonstrate that the proposed element is capable of yielding accurate results for the given problems. In addition, it is also concluded that in comparison to the elements developed by other researchers, this new formulation leads to more precise outcomes.
Abstract in English:This paper presents effects of boundary conditions and axial loading on frequency characteristics of rotating laminated conical shells with meridional and circumferential stiffeners, i.e., stringers and rings, using Generalized Differential Quadrature Method (GDQM). Hamilton's principle is applied when the stiffeners are treated as discrete elements. The conical shells are stiffened at uniform intervals and it is assumed that the stiffeners have similar material and geometric properties. Equations of motion as well as equations of the boundary condition are transformed into a set of algebraic equations by applying the GDQM. Obtained results discuss the effects of parameters such as rotating velocities, depth to width ratios of the stiffeners, number of stiffeners, cone angles, and boundary conditions on natural frequency of the shell. The results will then be compared with those of other published works particularly with a non-stiffened conical shell and a special case where angle of the stiffened conical shell approaches zero, i.e. a stiffened cylindrical shell. In addition, another comparison is made with present FE method for a non-rotating stiffened conical shell. These comparisons confirm reliability of the present work as a measure to approximate solutions to the problem of rotating stiffened conical shells.
Abstract in English:This paper presents analytical and mathematical modeling and optimization of the dynamic behavior of the fiber metal laminates (FMLs) subjected to low-velocity impact. The deflection to thickness (w/h) ratio has been identified through the governing equations of the plate that are solved using the first-order shear deformation theory as well as the Fourier series method. With the help of a two degrees-of-freedom system, consisting of springs-masses, and the Choi's linearized Hertzian contact model the interaction between the impactor and the plate is modeled. Thirty-one experiments are conducted on samples of different layer sequences and volume fractions of Al plies in the composite Structures. A reliable fitness function in the form of a strict linear mathematical function constructed. Using an ordinary least square method, response regression coefficients estimated and a zero-one programming technique proposed to optimize the FML plate behavior subjected to any technological or cost restrictions. The results indicated that FML plate behavior is highly affected by layer sequences and volume fractions of Al plies. The results also showed that, embedding Al plies at outer layers of the structure significantly results in a better response of the structure under low-velocity impact, instead of embedding them in the middle or middle and outer layers of the structure.
Abstract in English:This paper investigates the behaviour of axially loaded stiffened concrete-filled steel composite (CFSC) stub columns using the finite element software LUSAS. Modelling accuracy is established by comparing results of the nonlinear analysis and the experimental test. The CFSC stub columns are extensively developed using different special arrangements, number, spacing, and diameters of bar stiffeners with various steel wall thicknesses, concrete compressive strengths, and steel yield stresses. Their effects on the columns behaviour are examined. Failure modes of the columns are also illustrated. It is concluded that the parameters have considerable effects on the behaviour of the columns. An equation is proposed based on the obtained results to predict the ultimate load capacity of the columns. Results are compared with predicted values by the design code EC4, suggested equation of other researchers, and proposed equation of this study which is concluded that the proposed equation can give closer predictions than the others.
Abstract in English:This article intends to achieve a new formulation of beam vibration with quintic nonlinearity, including exact expressions for the beam curvature. To attain a proper design of the beam structures, it is essential to realize how the beam vibrates in its transverse mode which in turn yields the natural frequency of the system. In this direction, new powerful analytical method called Parameter Expansion Method (PEM) is employed to obtain the exact solution of frequency-amplitude relationship. Afterwards, it is clearly shown that the first term in series expansions is sufficient to produce a highly accurate approximation of mentioned system. Finally, preciseness of the present analytic procedures is evaluated in contrast with numerical calculations methods, giving excellent results.