Abstract in English:Abstract Free vibration responses of shear deformable functionally graded single/doubly curved panels under uniform, linear and nonlinear temperature fields are investigated in the present article. The micromechanical material model of functionally graded material is computed using Voigt model in conjunction with the power-law distribution to achieve the continuous gradation. The material properties are assumed to be the function of temperatures. The mid-plane kinematics of panel geometry is derived using the higher order shear deformation theory. The governing equation of the vibrated panel is obtained using Hamilton's principle. The desired solutions of free vibrated functionally graded shells are computed numerically using the suitable finite element steps. The convergence behaviour of the numerical results has been checked and validated by comparing the responses with that to available published literatura. The applicability of the proposed model has been highlighted by solving various numerical examples for different material and geometrical parameters and temperature fields.
Abstract in English:Abstract The stress intensity factor (SIF) and the degree of bending (DoB) are among the crucial parameters in evaluating the fatigue reliability of offshore tubular joints based on the fracture mechanics (FM) approach. The value of SIF is a function of the crack size, nominal stress, and two modifying coefficients known as the crack shape factor (Yc) and geometric factor (Yg). The value of the DoB is mainly determined by the joint geometry. These three parameters exhibit considerable scatter which calls for greater emphasis in accurate determination of their governing probability distributions. As far as the authors are aware, no comprehensive research has been carried out on the probability distribution of the DoB and geometric and crack shape factors in tubular joints. What has been used so far as the probability distribution of these factors in the FM-based reliability analysis of offshore structures is mainly based on assumptions and limited observations, especially in terms of distribution parameters. In the present paper, results of parametric equations available for the computation of the DoB, Yc, and Yg have been used to propose probability distribution models for these parameters in tubular K-joints under balanced axial loads. Based on a parametric study, a set of samples were prepared for the DoB, Yc, and Yg; and the density histograms were generated for these samples using Freedman-Diaconis method. Ten different probability density functions (PDFs) were fitted to these histograms. The maximum likelihood (ML) method was used to determine the parameters of fitted distributions. In each case, Kolmogorov-Smirnov test was used to evaluate the goodness of fit. Finally, after substituting the values of estimated parameters for each distribution, a set of fully defined PDFs were proposed for the DoB, crack shape factor (Yc), and geometric factor (Yg) in tubular K-joints subjected to balanced axial loads.
Abstract in English:Abstract Finite element analysis was used to investigate the impact behavior of the foam-cored sandwich shells under the ballistic impact. The ballistic limit, failure mode of the face-sheet and energy absorption of the uniform/graded core were discussed in this paper. Based on the impact phase diagrams, the effects of several factors (i.e. projectile shape and diameter, face-sheet curvature and thickness) on the normal/oblique impact behavior were analyzed in detail. Results indicate that blunter and larger projectiles, higher impact velocity and thicker face-sheets can significantly raise the impact-resistance performance of the targets. In addition, the behavior of ballistic impact becomes more complex as the result of the increasing oblique angle.
Abstract in English:Abstract A transition element is developed for the local global analysis of laminated composite beams. It bridges one part of the domain modelled with a higher order theory and other with a 2D mixed layerwise theory (LWT) used at critical zone of the domain. The use of developed transition element makes the analysis for interlaminar stresses possible with significant accuracy. The mixed 2D model incorporates the transverse normal and shear stresses as nodal degrees of freedom (DOF) which inherently ensures continuity of these stresses. Non critical zones are modelled with higher order equivalent single layer (ESL) theory leading to the global mesh with multiple models applied simultaneously. Use of higher order ESL in non critical zones reduces the total number of elements required to map the domain. A substantial reduction in DOF as compared to a complete 2D mixed model is obvious. This computationally economical multiple modelling scheme using the transition element is applied to static and free vibration analyses of laminated composite beams. Results obtained are in good agreement with benchmarks available in literature.
Abstract in English:Abstract The analytical approach is presented for both symmetric and anti-symmetric local buckling of the thin-plate in finite sizes and with a center crack under tension. An efficient classical solution based on the principle of minimum total potential energy was provided using only 2 and 1 degrees of freedom for symmetric and anti-symmetric modes and the linear elastic buckling loads are evaluated by the means of Rayleigh-Ritz method. In the pre-buckling state, a correction factor for the peak compressive stress in the finite cracked plates is defined with an empirical formula and used in the analytical solution of the buckling. To verify the analytical approach, a wide range of numerical results by aid of finite element method are provided herein and a comparison between theoretical results with the experimental work of other researchers has been done. Both numerical and experimental results accept the accuracy and validity of the presented analytical model.
Abstract in English:Abstract The use of thin-walled composite beams in Engineering has attracted great interest in recent years. Composite beams and other structural elements tend to have thin walls due to the high strength of the material. Other important aspect is that, even without reaching large strains and without overcoming the elastic limit of the material, such as beams present geometric nonlinear behavior due to their high slenderness, leading to large displacements and rotations. In this paper, a three-dimensional frame finite element for geometric nonlinear analysis of thin-walled laminated composite beams is presented. The finite element uses the Total Lagrangian formulation in order to allow the treatment of large displacements, but with moderated rotations. The constitutive matrix of the laminated beams is evaluated through a suitable thin-walled beam theory. In this theory, the effects of the couplings for several layups are considered, but the effects of the warping and transverse shear are neglected. Comparisons with numerical experiments demonstrate the very good accuracy of the proposed finite element.
Abstract in English:Abstract This paper investigates the performance of a three-dimensional multi-storey structure with Buckling Restrained Brace system (BRBs) under fire condition, using a sequentially coupled nonlinear thermal stress analysis. Efficiency of using BRBs in enhancing the strength and stiffness of a structural frame is compared with that of Ordinary Concentrically Bracing system (OCBs) under various fire scenarios. The proposed numerical model is verified by a series of full-scale fire tests carried out on an 8-storey structure at Cardington. The results indicate that the vertical movement of heated (buckled) column in the structural frame with BRBs is lesser than that with OCBs. Consequently, the tensile force and bending moment of the beam adjacent to the buckled column in the former is lesser than the latter. Also, BRB elements can perform better in redistributing the load sustained by heated columns without any buckling occurrence in the bracing member, in comparisons to the ordinary system. In general, it is observed that BRBs manifest an improved performance in re-stabilization of structural frame against fire for a longer period of heating time, such that a better fire resistance is offered to the whole building as compared to OCBs, due to a higher restraint provided onto the structure.
Abstract in English:Abstract The widespread use of tubular sections in regions like Western Europe and North America in addition structural and aesthetical reasons can be attributed to the high degree of development of their production technology. Despite this fact their use in Brazil in the past was limited to a few spatial roofs. Currently, the situation in the Brazilian market begins to change caused by the significant increase in the availability of structural hollow sections. This work presents an analysis of "KK" joints with circular hollow sections. A comparison between the analytical design formulations proposed by the Eurocode 3 Part 1.8, the 2nd edition of the CIDECT tubular joint design guide was performed. A finite element model was developed in the ANSYS program for each analysed joint typology. The modelling of a spatial truss made of circular hollow section elements was also performed to enable a comparison between a single joint and the response of the joint as a part of a full scale truss structure.
Abstract in English:Abstract This paper presents a study on the behaviour of welded "T" joints between RHS sections under brace axial loading. A finite element model was developed to investigate the influence of some geometrical variables on the joint's response. The brace load (always in tension) was incremented up to joint failure, while the chord was kept unloaded. In the companion paper (part II) a complementary study including chord axial loading is presented. The force-displacement curves corresponding to the different geometries are analyzed and compared, focusing on the failure loads and elastic stiffness. Different failure criteria are discussed and applied to the present curves and a comparison of the numerical results with the Eurocode 3 provisions is presented and discussed.
Abstract in English:Abstract This paper deals with the behaviour of welded "T" joints between RHS sections submitted to tension brace loading combined with chord axial loading. In the companion paper (part I) a finite element model and a study without axial load in the chord, focusing on the joint behaviour as a function of the significant geometrical variables, were presented. In this part II paper, tension loading on the brace is incremented up to the joint failure, but is combined with different chord load levels in tension or compression, that are kept constant for each case. The same geometries and geometric variables as in the companion paper are used, and therefore the influence of these features together with the chord load level (in tension or compression) on the connection's response is evaluated. The force-displacement curves from the different geometries and chord load levels are analysed and compared, with a special attention on the influence of the chord load on the joint resistance and stiffness. Finally, a comparison of the numerical results with the (Eurocode 3, 2005) and the newer (ISO 14346, 2013) provisions is presented and discussed.