Abstract in English:This paper presents both the analytical and theoretical investigations on ultimate load carrying capacity and behaviour of CFS unlipped channels with their ends fixed and subjected to axial compression. The numerical studies have been carried out in the elastic as well as in the plastic ranges of loading. The slenderness ratio of the channels chosen is 40, 80,100 and 120. Three different web depths [shallow, medium and deep] with five thicknesses have been chosen. In addition to the numerical studies, comparison with the design strengths predicted by using North American Standards for CFS structures. It is observed that the design strength predicted by the specifications are conservative for axially loaded columns. In the present investigation, an attempt is made to study the ultimate load carrying capacity and the mode of failure. Load versus axial shortening behaviour has been studied for various slenderness ratios for a few specimens.
Abstract in English:The uniform deformation theory (UDT) is a relatively new concept in structural seismic design optimization. However, the results of optimization based on this theory have not yet been compared with other optimization techniques such as metaheuristics, and the optimality of the designs has been proved only by comparing the results with the conventional designs. This paper presents a new algorithm based on the UDT to performance-based design optimization (PBDO) of steel moment frames. In order to verify robustness of this method, the achieved results of PBDO for two baseline steel moment frames are compared with three metaheuristics consisting of genetic algorithm (GA), ant colony optimization (ACO), and particle swarm optimization (PSO). The results indicate that the optimization based on UDT provides a much higher convergence rate to the optimum design compared with metaheuristics.
Abstract in English:An experimental procedure is carried out to investigate response features of semi-deep reinforced concrete (RC) beams with dominant static shear failure subjected to low-velocity impact dynamic load both in intact and retrofitted cases. Built specimens have scaled geometry and material properties preserving physical similarity with full-scale members and are strengthened using externally bonded carbon fiber reinforced polymer (CFRP) sheets. Conducted tests gather reliable and robust data revealing notable stiffness and strength recovery within skin attachment. Desired performance criterion is detected here as concrete flexural cracking along span only when brittle shear collapse is prevented. Peak absorbed impulse capacity is attained for unidirectional carbon fiber retrofit. Stiffness is recovered initially during first impacts and then starts degrading due to rupture of horizontal fibers in cross-ply retrofit, but provided stiffness is stable for unidirectional retrofit during all impacts.
Abstract in English:In this paper, squeeze film damping in a micro-beam resonator based on micro-polar theory has been investigated. The proposed model for this study consists of a clamped-clamped micro-beam bounded between two fixed layers. The gap between the micro-beam and layers is filled with air. As fluid behaves differently in micro scale than macro, the micro-scale fluid field in the gap has been modeled based on micro-polar theory. Equation of motion governing transverse deflection of the micro- beam based on modified couple stress theory and also non-linear Reynolds equation of the fluid field based on micropolar theory have been non-dimensionalized, linearized and solved simultaneously in order to calculate the quality factor of the resonator. The effect of micropolar parameters of air on the quality factor has been investigated. The quality factor of the of the micro-beam resonator for different values of non-dimensionalized length scale of the beam, squeeze number and also non-dimensionalized pressure has been calculated and compared to the obtained values of quality factor based on classical theory.
Abstract in English:In the current research to model anisotropic asymmetric sheet metals a new non-AFR criterion is presented. In the new model, Modified Yld2000-2d proposed by Lou et al. (2013) is considered as yield function and Yld2000-2d proposed by Barlat et al. (2003) is considered as plastic potential function. To calíbrate the presented criterion, the yield function which is a pressure dependent criterion requiers ten directional yield stresses such as uniaxial tensile stresses in three directions of 0º, 45º, 90º, uniaxial compressive yield stresses in six directions of 0º, 15º, 30º, 45º, 75º, 90º from the rolling direction along with biaxial yield stress. Moreover, the plastic potential function which is a pressure indepedent criterion needs eight experimental data points such as tensile R-values in seven directions of 0º, 15º, 30º, 45º, 60º, 75º, 90º from the rolling direction and also biaxial tensile R-value. Finally with comparing the obtained results with experimental data points, it is shown that the presented non-AFR criterion predicts compressive yield stress, biaxial tensile yield stress and R-values more accurately than Modified Yld2000-2d and it would be considered as a new criterion for anisotropic asymmetric metals.
Abstract in English:A three-dimensional finite element model used to simulate the bolted joint is created using ABAQUS package. The stress concentration factors at the roots of the thread are first studied with a preload of 38.4 kN. Under harmonic transverse shear displacement, not only the stress variations at ten specified points of the first thread but also contact conditions between the contacting surfaces are studied. By changing the preload value, relative displacement, the coefficient of friction between the two clamped plates successively and the loading frequency, their effects on the hysteresis loops of the transverse load versus the relative displacement of the joint are then analyzed. Finally the hysteresis loops are produced by the Masing model. It is found that due to the greatest stress concentration factor, fatigue failure will occur at the root of the first thread. With the increase of preload value, the amplitude of displacement and the coefficient of friction, frictional energy dissipation of the joint increases. Very good agreement is achieved between the hysteresis loops produced from the fourth-order Masing model and the detailed ABAQUS model and therefore the fourth-order Masing model can replace the time-consuming finite element model.
Abstract in English:This paper presents low velocity impact response of functionally graded pretwisted conical shells. The modiﬁed Hertzian contact law which accounts for permanent indentation is utilized to compute the contact force and other impact parameter. The time dependent equations are solved by Newmark's time integration scheme. An eight noded isoparametric quadratic element is employed in the present ﬁnite element formulation. A parametric study is carried out to investigate the effects of triggering parameters like initial velocity of impactor, twist angle, oblique impact angle, location of impact for Stainless Steel-Nickel functionally graded conical shell subjected to low velocity impact.
Abstract in English:The convergence characteristic of the conventional two-noded Euler-Bernoulli piezoelectric beam finite element depends on the configuration of the beam cross-section. The element shows slower convergence for the asymmetric material distribution in the beam cross-section due to 'material-locking' caused by extension-bending coupling. Hence, the use of conventional Euler-Bernoulli beam finite element to analyze piezoelectric beams which are generally made of the host layer with asymmetrically surface bonded piezoelectric layers/patches, leads to increased computational effort to yield converged results. Here, an efficient coupled polynomial interpolation scheme is proposed to improve the convergence of the Euler-Bernoulli piezoelectric beam finite elements, by eliminating ill-effects of material-locking. The equilibrium equations, derived using a variational formulation, are used to establish relationships between field variables. These relations are used to find a coupled quadratic polynomial for axial displacement, having contributions from an assumed cubic polynomial for transverse displacement and assumed linear polynomials for layerwise electric potentials. A set of coupled shape functions derived using these polynomials efficiently handles extension-bending and electromechanical couplings at the field interpolation level itself in a variationally consistent manner, without increasing the number of nodal degrees of freedom. The comparison of results obtained from numerical simulation of test problems shows that the convergence characteristic of the proposed element is insensitive to the material configuration of the beam cross-section.
Abstract in English:In many engineering structures different energy absorption systems may be used to improve crashworthiness capability of the system and to control damages that may occur in a system during an accident. Therefore, extensive research has been done on the energy-absorbing cells. In this paper, energy absorption in tapered thick walled tubes has been investigated. As a practical case, studies have been focused on the crush element of Siemens ER24PC locomotive. To investigate performance of this part at collision time, it has been modeled in Abaqus software and its collision characteristics have been evaluated. Considering that the crash element is folded at time of collision, an analytical approach has been presented for calculation of instantaneous folding force under axial load. Basis of this method is definition and analysis of main folding mechanism and calculation of average folding force. This method has been used for validation of the results of numerical solution. Since sheet thickness of the crash element is high and may be ruptured at time of collision, some damage models have been used for numerical simulations. One of the three damage models used in this paper is available in the software and coding has been done for two other damage models and desirable damage model has been specified by comparing results of numerical solution with results of laboratory test. In addition, authenticity of the desirable damage model has been studied through ECE R 66 standard. To improve crashworthiness characteristic some attempts, such as use of metal foam and creation of trigger in suitable situations to reduce maximum force resulting from collision, have been performed. Finally though different simulation optimal crush element has been introduced and its performance and efficiency have been evaluated.