Abstract in English:In the present paper, an exponential shear deformation theory is used to determine the natural frequencies and critical buckling loads of orthotropic plates. The theory accounts for a parabolic distribution of the transverse shear strains across the thickness, and satisfies the zero traction boundary conditions on the top and bottom surfaces of the plate without using shear correction factors. The in-plane displacement field uses an exponential function in terms of thickness coordinate to include the effect of shear deformation and rotary inertia. Governing equations and boundary conditions are derived from the dynamic version of principle of virtual work. The Navier type solution is employed for solving the governing equations of simply supported square orthotropic plates. The results obtained using present higher order shear deformation theory are found to be agree well with those obtained by other several existing higher order theories for analyzing the buckling and free vibration behaviour of orthotropic plates.
Abstract in English:Carbon nano-tube (CNT) is applied to fabricate nano-probes, nano-switches, nano-sensors and nano- actuators. In this paper, a continuum model is employed to obtain the nonlinear constitutive equation and pull-in instability of CNT-based probe/actuators, which includes the effect of electrostatic interaction and intermolecular van der Waals (vdW) forces. The modified Adomian decomposition (MAD) method is applied to solve the nonlinear governing equation of the CNT-based actuator. Furthermore a simple and useful lumped parameter model was developed to investigate trends for various pull-in parameters. The influence of the vdW force and the geometrical dimensionless parameter on the pull-in deflection and voltage of the system is investigated. The obtained results are compared with those available in the literature as well as numerical solutions. The results demonstrate that our developed continuum based model is in good agreement with experimental results.
Abstract in English:Thin-walled structures like crash boxes may be used as energy absorption members in automotive chassis. There have been many studies addressing the behaviors of energy absorption members on frontal crash. These researches have attempted to predict the energy absorption and maximum impact load in shell structures. The energy absorption and maximum impact load depend on many parameters including boundary condition, history of plastic deformation during metalworking, geometry; and material and impact energy (i.e. mass and velocity of the striker). This study examined the crash behavior of square tube made of the extruded aluminum alloy 6063T4 using an elastic boundary condition -instead of rigid boundary condition- on the bottom of a crash box, In addition, the effect of elastic boundary condition on energy absorption of square tubes under the impact load was investigated both numerically and experimentally. Results showed that using elastic boundary could change the deformation mode and decrease the maximum impact load. Further, a high correlation between the numerical and experimental results validated the findings of the study.
Abstract in English:Constrained optimization is very important issue in engineering design. The problem of constrained optimization contains the objective function with linear and nonlinear constraint equations. In this paper the Improved Cuckoo Search (ICS) algorithm has been applied for solving problems of constrained engineering optimization, which gives better solutions than the standard CS algorithm and the other optimization algorithms used in solving engineering problems from the literature. In the proposed ICS algorithm, dynamic change of parameters of probability and step size is introduced, which are constant in the standard algorithm.
Abstract in English:The buckling behaviour of pin ended cold-formed steel lipped channel columns affected by local / distortional / global buckling mode interaction under axial loading is simulated by using finite element software ABAQUS, and the results are compared with the test results available in the literature. The comparisons show that the proper analysis model can simulate the buckling behaviour and ultimate capacity of cold-formed steel columns. Then a parametric analysis is carried out for 15 column geometries of 3 yield stress values of different dimension, thickness and lengths. The cross sectional dimensions and length of the specimen have been chosen such that to have almost equal local, distortional and global critical buckling stresses by using the CUFSM software. The selected sections also satisfied the limitations given for pre-qualified sections in Direct Strength Method (DSM). After comparing the FEM column ultimate loads with the estimates predicted by the current Direct Strength Method (DSM) design curves against local, distortional and global failures, which clearly shows that they lead to inaccurate and often very unsafe ultimate load estimates. At the end, a design recommendation is made for current design practice of evaluating the ultimate strength of the lipped channel columns.
Abstract in English:In this work it is presented a coupling between the Boundary Element Method (BEM) and the Finite Element Method (FEM) for two-dimensional elastostatic analysis of frame-solid interaction. The BEM is used to model the matrix while the reinforcement is modeled by the FEM. Regarding the coupling formulation a third degree polynomial is adopted to describe the displacement and rotations of the reinforcement, while a linear polynomial is used to describe the contact force among the domain (matrix) and the reinforcement. Perfect bounding contact forces are improved by means of redundant equations and Least squares method. Slip-bounding with two and three paths written as function of relative displacement are used to calculate the transmitted contact forces. Examples are used to demonstrate that the proposed slip-bounding procedure regularizes the contact force behavior.
Abstract in English:The pre-existing cracks in the brittle substances seem to be the main cause of their failure under various loading conditions. In this study, a simultaneous analytical, experimental and numerical analysis of crack propagation, cracks coalescence and failure process of brittle materials has been performed. Brazilian disc tests are being carried out to evaluate the cracks propagation paths in rock-like Brazilian disc specimens containing single and double cracks (using rock-like specimens which are specially prepared from Portland Pozzolana Cement (PPC), fine sands and water in a rock mechanics laboratory). The failure load of the pre-cracked disc specimens are measured showing the decreasing effects of the cracks and their orientation on the final failure load. The same specimens are numerically simulated by a higher order indirect boundary element method known as displacement discontinuity method. These numerical results are compared with the existing analytical and experimental results proving the accuracy and validity of the proposed numerical method. The numerical and experimental results obtained from the tested specimens are in good agreement and demonstrate the accuracy and effectiveness of the proposed approach.
Abstract in English:Depending on the type of structural analysis required, any moment-rotation curve representation can be used; these include linear, bilinear, multi-linear and nonlinear representations. The most accurate representation uses continuous nonlinear functions. In this study, two distinct approaches are proposed to account for the complex hysteretic behavior of column-base connections. The performance of the two approaches is examined and is then followed by a discussion of their merits and deficiencies. To capitalize on the merits of both mathematical and informational representations, a new approach, a composed modeling framework, is developed and demonstrated through modeling column-base connections.In the composed framework, a conventional mathematical model is complemented by the informational methods. The role of informational methods is to model aspects that the mathematical model leaves out. The potential of the composed method is illustrated through modelingcomplex hysteretic behavior of column-base connections.
Abstract in English:In this paper, a numerical method for solution of the free vibration of beams governed by a set of second-order ordinary differential equations of variable coefficients, with arbitrary boundary conditions, is presented. The method is based on numerical integration rather than the numerical differentiation since the highest derivatives of governing functions are chosen as the basic unknown quantities. The kernelsof integral equations turn out to be Green's function of corresponding equation with homogeneous boundary conditions. The accuracy of the proposed method is demonstrated by comparing the calculated results with those available in the literature. It is shown that good accuracy can be obtained even with a relatively small number of nodes.
Abstract in English:This study presents a numerical investigation into the behaviour of short concrete filled steel tubular (CFST) columns. Three Dimensional Nonlinear finite element analysis of the compression process is performed using commercial software ABAQUS v6.9 (2009). Steel tubes of different geometries and in-filled with different grades of concrete are chosen for modelling from literature. The proposed FE model is validated by comparing its results with those of the corresponding experimental specimens. The model is further used to study the variation of radial confining pressure f cp provided by the steel tube to the concrete core. It is observed that the value of f cp varies widely throughout the length of the CFST, with the values in the area adjacent to top and bottom platens being markedly higher than the values in-between due to the end restraint provided by the machine platens. This is in contrast to the present confined concrete model which uses a uniform value of confining pressure throughout the height. Effect of effective length of column and interfacial friction present between the platen and specimen are found to be negligible on behaviour of short CFST column.