Abstract in English:Abstract In this paper, the fatigue behavior of the metallic welded U-shape specimens subjected to cyclic loading have been investigated via experimental and numerical analysis. To do so, two sets of the spot welded specimens with different sizes were prepared and fatigue tests were conducted under the various cyclic loads. The crack propagation is numerically examined by using the stress intensity factor values achieved from FE analyses. The modified Paris and Forman-Newman-De Koning models were used to estimate the fatigue crack growth rate. The results indicate that the fatigue life of specimens decreases with any increase in load level.
Abstract in English:Abstract Over the past decades a growing demand and interest has stimulated many researchers to investigate different aspects of steel plate shear walls (SPSWs). The structural performance of steel shear walls with sinusoidal corrugated plate infills is investigated in this study. Finite element (FE) analysis was adopted using ANSYS software, wherein flat and corrugatedshear walls - with different thicknesses, various corrugation numbers and angles - were modeled under monotonic and cyclic loads. Results and findings of this study indicate that geometrical variations developed through corrugation can be effective on the capacity, rigidity, and post-yielding responses of such corrugated-web lateral force-resisting systems. In addition, proper design and detailing can result in desirable structural behavior and seismic performance of SPSWs with sinusoidal corrugated infill plates.
Abstract in English:Abstract Clearance always exists in actual joint due to many uncertainties such as machining tolerance, assemblage and load deformation. The main purpose of this paper is to propose a computational and experimental study on the dynamic characteristics of a planar multibody mechanical system with joint clearance. For this purpose, a suitable dynamic model plays a crucial role in simulating the overall performance of the mechanical systems. To describe the interaction in joints with clearance, the normal contact model is established based on the Lankarani-Nikravesh contact force model, while the friction effect is conducted using the Coulomb friction model. Meanwhile, the experimental platform is set up and a planar mechanism with clearance joint is employed as a model mechanism. The obtained results demonstrate that the dynamic behavior of the mechanism can be effectively predicted by this method. Furthermore, the effects of the rotational speed of crank shaft and size of joint clearance on the dynamic response of the mechanism are investigated.
Abstract in English:Abstract The good damping performance and inherent stability of viscoelastic materials in relatively broad frequency bands, besides cost effectiveness, offers many possibilities for practical engineering applications. However, for viscoelastic dampers subjected to dynamic loadings superimposed on static preloads, especially when good isolation characteristics are required at high frequencies, traditional design guidelines can lead to poor designs due to the rapidly increasing rate of temperature change inside the material. This paper is devoted to the numerical and experimental investigation in the degradation of the stiffness and capacity of a viscoelastic material induced by the thermal runaway phase, when it is subjected to dynamic and static loads simultaneously. After the theoretical background, the obtained results in terms of the temperature evolutions at different points within the volume of the material and the hysteresis loops for various static preloads are compared and the main features of the proposed study are highlighted.
Abstract in English:Abstract This work addresses an accurate and detailed axial static load dependence linearly elastic free vibration analysis of cylindrical helical springs based on the theory of spatially curved bars and the transfer matrix method. For a continuous system, governing equations comprise coupled vibration modes namely transverse vibrations in two orthogonal planes, torsional and axial vibrations. The axial and shear deformation effects together with the rotatory inertia effects are all considered based on the first order shear deformation theory and their effects on the frequencies are investigated. The effects of the initial stress resultants on the frequencies are also studied. After buckling, forward-shifting phenomenon of higher frequencies is noticeably demonstrated. It is also revealed that a free/forced vibration analysis with an axial static load should not be performed individually without checking buckling loads.
Abstract in English:Abstract The projectile impact resistance of sandwich panels with cellular cores with different layer numbers has been numerically investigated by perpendicular impact of rigid blunt projectile in ABAQUS/Explicit. These panels with corrugation, hexagonal honeycomb and pyramidal truss cores are impacted at velocities between 50 m/s and 202 m/s while the relative density ranges from 0.001 to 0.15 The effects of core configuration and layer number on projectile impact resistance of sandwich panels with cellular cores are studied. At low impact velocity, sandwich panels with cellular cores outperform the corresponding solid ones and non-montonicity between relative density and projectile resistance of sandwich panels is found and analyzed. Multiplying layer can reduce the maximum central deflection of back face sheet of the above three sandwich panels except pyramidal truss ones in high relative density. Hexagonal honeycomb sandwich panel is beneficial to increasing layer numbers in lowering the contact force and prolonging the interaction time. At high impact velocity, though corrugation and honeycomb sandwich panels are inferior to the equal-weighted solid panels, pyramidal truss ones with high relative density outperform the corresponding solid panels. Multiplying layer is not the desirable way to improve high-velocity projectile resistance.
Abstract in English:Abstract The general mathematical model of a flexible connection of links by means of spring-damping elements is presented in the paper. The formalism of homogeneous transformation matrices is used to derive formulas for the energy of spring deformation and the Rayleigh dissipation function of the spring-damping elements. The formulas have convenient forms to connect them to Lagrange equations of the second order. The replacement models of the spherical and revolute joint are presented as a particular case of the general model and are used for dynamics analysis of a one-DOF RSRRP linkage mechanism. The numerical results obtained here using the replacement models were compared with the results from the cut-joint technique.
Abstract in English:Abstract This paper presents a Backtracking Search Optimization algorithm (BSA) to simultaneously optimize the size, shape and topology of truss structures. It focuses on the optimization of these three aspects since it is well known that the most effective scheme of truss optimization is achieved when they are simultaneously considered. The minimization of structural weight is the objective function, imposing displacement, stress, local buckling and/or kinematic stability constraints. The effectiveness of the BSA at solving this type of optimization problem is demonstrated by solving a series of benchmark problems comparing not only the best designs found, but also the statistics of 100 independent runs of the algorithm. The numerical analysis showed that the BSA provided promising results for the analyzed problems. Moreover, in several cases, it was also able to improve the statistics of the independent runs such as the mean and coefficient of variation values.
Abstract in English:Abstract In this paper, free vibration analysis of rotating functionally graded cylindrical shells with orthogonal stiffeners is presented. Based on Love's first approximation theory and smeared stiffeners technique, the governing equations of motion which take into account the effects of initial hoop tension and also the centrifugal and Coriolis forces due to rotation are derived. The influence of the power law index, the stiffener's height-to-width ratio, the circumferential wave numbers, the shell length-to-radius ratio, and the shell radius-to-thickness ratio on the natural frequencies of the simply supported rotating stiffened functionally graded cylindrical shell are investigated. To validate the present analysis, comparisons are made with those available in the literature for particular cases; very good agreements are achieved.
Abstract in English:Abstract This paper presents results of eight experimental tests carried to evaluate the mechanical performance of unconnected "W" stirrups. Reinforced concrete wide beams were tested and their characteristics were idealized to represent column strips in flat slab buildings. The main variables were: the type of shear reinforcement; the shear span to effective depth ratio (a v/d); and the flexural (ρl) and shear (ρw) reinforcement ratios. In general, both the response and the shear resistance of the structural elements with unconnected "W" stirrups was similar to those elements with vertical closed stirrups. Increments of shear resistance of up to 84% were achieved, indicating that they have high potential for use as shear reinforcement in slab-column connections.