Abstract in English:Abstract Bolted end-plate steel connections have become more popular due to ease of fabrication. This paper presents a three dimension Finite Element Model (FEM), using the multi-purpose software ABAQUS, to study the effect of different geometrical parameters on the ultimate behavior of the connection. The proposed model takes into account material and geometrical non-linearities, initial imperfection, contact between adjacent surfaces and the pretension force in the bolts. The Finite Element results are calibrated with published experimental results ''briefly reviewed in this paper'' and verified that the numerical model can simulate and analyze the overall and detailed behavior of different types of bolted end-plate steel connections. Using verified FEM, parametric study is then carried out to study the ultimate behavior with variations in: bolt diameter, end-plate thickness, length of column stiffener, angle of rib stiffener. The results are examined with respect to the failure modes, the evolution of the resistance, the initial stiffness, and the rotation capacity. Finally, the ultimate behavior of the bolted end-plate steel connection is discussed in detail, and recommendations for the design purpose are made.
Abstract in English:Abstract In this work we present a simple, fast technique for generating particle packs at high packing ratios aiming at the simulation of granular compacts via the discrete element method (DEM). We start from a random sequence addition particle generation algorithm to generate a "layer" of non-overlapping spherical particles that are let to evolve dynamically in time under the action of "compacting" or "jamming" pseudo forces. A "layer-by-layer" approach is then followed to generate multiple layers on top of each other. In the end, very dense packs with pre-defined bulk shapes and sizes (e.g. rectangles in two dimensions and prisms in three dimensions) are achieved. The influence of rolling motion (with particle rotation and spin) along with inter-particle friction on the density and ordering of the generated packs is assessed. Both congruent and inhomogeneous packs (with respect to particle sizes) are created and their packing properties evaluated. We believe that simple techniques for fast generation of particle packs at high packing ratios are essential tools for the DEM simulation of granular compacts.
Abstract in English:Abstract A human femur model, submitted to static loads, is analyzed through the utilization of three material constitutive relationships, namely: isotropic, transversally isotropic and orthotropic. The influence of bone anisotropy with respect to principal stress/strain distribution on human femur external surface was accessed through the use of analytical and finite element approaches. The models results show that the principal angles at a medial path bone surface have a good correlation with human femur bone lamellae angles.
Abstract in English:Abstract In this paper, the critical axial speeds of three types of sigmoid, power law and exponential law functionally graded plates for both isotropic and orthotropic cases are obtained via a completely analytic method. The plates are subjected to lateral white noise excitation and show evidence of large deformations. Due to randomness, the conventional deterministic methods fail and a statistical approach must be selected. Here, the probability density function is evaluated analytically for prescribed plates and used to investigate the critical axial velocity of them. Specifically the effect of in-plane forces, mean value of lateral load and the material property on the critical axial speed are studied and discussed for both isotropic and orthotropic functionally graded plates. Since the governing equation is transformed to a non dimensional format, the results can be used for a wide range of plate dimensions. It is shown that the material heterogeneity palys an essential and significant role in increasing or decreasing the critical speed of both isotropic and orthotropic functionally graded plates.
Abstract in English:Abstract In this paper, analytical couple-stress solution for size-dependent large-amplitude vibrations of FG (functionally-graded) tapered-nanobeams is presented. Using the modified couple-stress theory, the small scale effects are accounted for. Employing the Homotopy-Pade Analysis Method, efficient and accurate analytical expressions for the deflection and non-linear frequencies of the both single and double tapered nanobeam are presented. Very good agreement is observed between the present work results and some available results reported in the literature. This study may be helpful to investigate the size-dependent mechanical properties of MEMS\NEMS. Therefore, the proposed analytical solution can be used as an efficient tool for the material or geometrical parametric studies of small scale devices consisting of beams for their design and optimization which involves a large number of simulations.
Abstract in English:Abstract To measure the aerodynamic and hydrodynamic forces and moments acting on scaled models in water and wind tunnel tests, multi-component strain gauge force and moment balance are usually used. Their performance and accuracy largely depends on the rig and calibration method, including the load table (design matrix) and analysis of experimental data. In this article, for the calibration of a six-component balance, a calibration procedure using the Box-Behnken design (BBD) of experiments was developed. In the suggested design matrix, in addition to all possible combinations of the two-component load of the six component load (Test vectors with two active factors), the pure loads (test vectors with one active factor) are also used. The implementation of the design matrixwas done using a calibration rig, which has the ability to perform formal experimental design techniques completely. The obtained experimental data were fitted with second-order equations using regression analysis. The statistical significance of independent variables and interactions was tested using the analysis of variance (ANOVA) with 95% confidence (α = 0.05). The results of residuals indicate that the suggested model sufficiently predicts the responses as a function of input factors. The comparison between the Modified Box-Behnken design (MBBD) and BBD calibrations indicates that the MBBD method estimates the data more accurate. The results show that the MBBD method is the most appropriate method compared to the existing methods for calibrating balance in this paper.
Abstract in English:Abstract In this paper vibration behavior of a fluid-conveying cracked pipe surrounded by a visco-elastic medium has been considered. During this work, the effect of an open crack parameters and flow velocity profile shape inside the pipe on natural frequency and critical flow velocity of the system has been analytically investigated. An explicit function for the local flexibility of the cracked pipe has been offered using principle of the fracture mechanics. Comparison between the results of the present study and the experimental data reported in the literature reveals success and high accuracy of the implemented method. It is demonstrated that the existence of the crack in the pipe, decreases the natural frequency and the critical flow velocity so that the system instability onsets at a lower flow velocity in comparison with the intact pipe. Results indicate that the flow velocity profile shape inside the pipe caused by the viscosity of real fluids, significantly affects the critical flow velocity of both intact and fluid-conveying cracked pipe. For instance, as the flow-profile-modification factor decreases from 1.33 to 1.015, the dimensionless critical flow velocity of intact clamped-clamped pipe increases from 5.45 to 6.24.
Abstract in English:Abstract In this Paper, a theory of single sagging planer weightless elasto-flexible cables is proposed. In reference to the instantaneous natural state, hypoelastic rate- type constitutive equations and third-order nonlinear differential equations of planer motion for massless cables with nodal masses are derived. New concepts like configurational complementary potential and contra-gradient principles are proposed. Typical dynamic response of these elastic cables with different sustained loads, axial rigidity and sag/span ratios is determined. Modal, subharmonic and internal resonances, jump and beat phenomena, etc., a re predicted. A new mode of damping of 'free' vibration of the system perturbed from its equilibrium state is identified. Significance of the proposed theory of weightless sagging elasto-flexible cables is discussed.
Abstract in English:Abstract This study deals with the dynamic behavior of a cracked beam subjected to a concentrated force traveling at a constant velocity. Dynamic analyses for a hinged-hinged cracked beam resting on elastic supports under the action of a moving load are carried out by the finite element method. For the beam having rectangular cross-section, element formulation for crack element is developed by using the principles of fracture mechanics. In the numerical analysis, Newmark integration method is employed in order to calculate the dynamic response of the beam. The effects of crack depth, crack location, elastic support and load velocity on the dynamic displacements calculated for different locations on the beam are investigated. The results related to the dynamic response of the beam are presented in 3D graphs.
Abstract in English:Abstract Based on dynamic direct tensile tests, splitting tests and spalling tests, it is found that the experimental tensile strength of concrete-like materials greatly increases with loading-rate. This kind of dynamic tensile strength enhancement may be caused by the combination influence of the inertia effect, real rate effect and end friction effect (here the end friction effect is only existed in splitting and spalling tests). To further investigate the influence degree of real rate effect for concrete-like materials in dynamic tensile tests, this paper conducts systematically dynamic tensile experiments, viz. dynamic direct tensile tests, splitting tests and spalling tests. At the same time, numerical dynamic tensile tests are employed to analyze the mechanical characteristics of concrete-like materials. A hydrostatic pressure dependent model, the Drucker-Prager constitutive model, is used for concrete-like material specimens, which can consider the influence of inertia effect. In the numerical model, the specimen is set to be rate-independent, thus the predicted dynamic tensile strength of specimens is free of the real rate effect. The end friction effect is also taken into account in the numerical analysis of dynamic splitting and spalling tests. It is found that the dynamic tensile strength of concrete-like materials in numerical simulations does not varies obviously with the loading-rate, indicating that the inertia effect and end friction effect have little contributions to the dynamic tensile strength enhancement of concrete-like materials. Therefore, the real rate effect dominates the dynamic tensile strength enhancement of concrete-like materials in laboratory tests, but the inertia effect and end friction effect do not.