Abstract in English:In this paper, two efficient elements for analyzing thin plate bending are proposed. They are a triangular element (THS) and a quadrilateral element (QHS), which have 9 and 12 degrees of freedom, respectively. Formulations of these elements are based on hybrid variational principle and analytical homogeneous solution of thin plate equation. Independent fields in hybrid functional are internal stress and boundary displacement field. The internal stress field has been calculated using analytical homogeneous solution and boundary field is related to the nodal degree of freedoms by the boundary interpolation functions. To calculate these functions, the edges of element are assumed to behave like an Euler-Bernoulli beam. The high accuracy and efficiency of the proposed elements are demonstrated in the severe tests.
Abstract in English:This study examines the effect of electric and magnetic field on torsional waves in hetrogeneous viscoelastic cylindrically aeolotropic tube subjected to initial compression stresses. A new equation of motion and phase velocity of torsional waves propagating in cylindrically aeolotropic tube subjected to initial compression stresses, nonhomogeneity, electric and magnetic field have been derived. The study reveals that the initial stresses, nonhomogeneity, electric and magnetic field present in the aeolotropic tube of viscoelastic solid have a notable effect on the propagation of torsional waves. The results have been discussed graphically. This investigation is very significant for potential application in various fields of science such as detection of mechanical explosions in the interior of the earth.
Abstract in English:Generally, Railway bridges are long structures which have different responses against different loads of train. Applied loads of train on railroad bridges are different in terms of axle loads speed, and annual passed tonnages and they have quite different dynamic behavior in comparison with road bridges. Most researches are basically focused on the quasi-static analysis. Therefore in these researches, the effect of load speed has been neglected. Nowadays with the development of rail transport systems, the study of dynamic behavior of bridges under the different load speed is necessary. Also, the dynamic behavior of curved bridges is different than straight ones. In this paper, vertical and torsional vibrations of a curved beam have been studied with considering vertical, horizontal load and eccentricity of load than centerline of bridge. Also the considered parameters in this research are radius of curvature, track irregularity, vehicle speed and bridge span.
Abstract in English:Reduction in traffic congestion and overall number of accidents, especially within the last decade, can be attributed to the enormous progress in active safety. Vehicle path following control with the presence of driver commands can be regarded as one of the important issues in vehicle active safety systems development and more realistic explanation of vehicle path tracking problem. In this paper, an integrated driver/DYC control system is presented that regulates the steering angle and yaw moment, considering driver previewed path. Thus, the driver previewed distance, the heading error and the lateral deviation between the vehicle and desired path are used as inputs. Then, the controller determines and applies a corrective steering angle and a direct yaw moment to make the vehicle follow the desired path. A PID controller with optimized gains is used for the control of integrated driver/DYC system. Genetic Algorithm as an intelligent optimization method is utilized to adapt PID controller gains for various working situations. Proposed integrated driver/DYC controller is examined on lane change manuvers andthe sensitivity of the control system is investigated through the changes in the driver model and vehicle parameters. Simulation results show the pronounced effectiveness of the controller in vehicle path following and stability.
Abstract in English:This paper presents a new approach to simultaneously obtain the optimal design parameters of tensegrity structures, including pre-stress force and sectional area of elements. The proposed method is based on minimizing the static compliance in terms of some linear and nonlinear constraints using a genetic algorithm tool. This work is devoted to optimize the concurrent cross sectional area of element and pre-stress of a tensegrity system which works under the applied external loading along with a fixed topology and shape. An increase in the rigidity of systems is one of the outcomes of modifying of tensegrity structures according to optimal design parameters. The validation, efficiency and characteristics of proposed algorithm to find the optimum values for design variables of tensegrity structures is tested through three known tensegrity structures.
Abstract in English:Here Fundamental Frequency is the main factor used to calculate the vibration of a vehicle when passing across a bridge. With knowledge of the fundamental frequency, bridges can be evaluated and designed in such a manner so as to avoid the critical range of 1.5 Hz to 4.5 Hz, which is occupied by most vehicles. Therefore it is crucial to develop a reliable method to estimate the fundamental frequency of bridges. To overcome the above issue, numerical analysis combined with a theoretical method is applied to estimate the fundamental frequency of multicell box-girder bridges. The effect of span-length, number of boxes and skew angle on the estimation of this factor is discussed. Finally, reliable expressions are proposed to predict the first fundamental frequency of this type of bridge, and the accuracy of the expressions is verified. The results indicate that the fundamental frequency decreases when span length increases, due to development of crack as well as decrease stiffness of girders.
Abstract in English:In this study, the vibration behavior of annular and circular graphene sheet coupled with temperature change and under in-plane pre-stressed is studied. Influence of the surrounding elastic medium 011 the fundamental frequencies of the single-layered graphene sheets (SLGSs) is investigated. Both Winkler-type and Pasternak- type models are employed to simulate the interaction of the graphene sheets with a surrounding elastic medium. By using the nonlocal elasticity theory the governing equation is derived for SLGSs. The closed-form solution for frequency vibration of circular graphene sheets lias been obtained and nonlocal parameter, inplane pre-stressed, the parameters of elastic medium and temperature change appears into arguments of Bessel functions. The results are subsequently compared with valid result reported in the literature and the molecular dynamics (MD) results. The effects of the small scale, pre-stressed, mode number, temperature change, elastic medium and boundary conditions on natural frequencies are investigated. The non-dimensional frequency decreases at high temperature case with increasing the temperature change for all boundary conditions. The effect of temperature change 011 the frequency vibration becomes the opposite at high temperature case in compression with the low temperature case. The present research work thus reveals that the nonlocal parameter, boundary conditions and temperature change have significant effects on vibration response of the circular nanoplates. The present results can be used for the design of the next generation of nanodevices that make use of the thermal vibration properties of the graphene.
Abstract in English:Numerical study of concrete-filled steel composite (CFSC) stub columns with steel stiffeners is presented in this paper. The behaviour of the columns is examined by the use of the finite element software LUSAS. Results from nonlinear finite element analyses are compared with those from corresponding experimental tests which uncover the reasonable accuracy of the modelling. Novel steel stiffeners are used in the CFSC stub columns of this study. The columns are extensively developed considering three different special arrangements of the steel stiffeners with various number, spacing, and widths of the stiffeners. The main variables are: (1) arrangement of the steel stiffeners (C1, C2, and C3); (2) number of the steel stiffeners (2 and 3); (3) spacing of the steel stiffeners (50 mm and 100 mm); (4) width of the steel stiffeners (50 mm, 75 mm, and 100 mm); (5) steel thickness (2 mm, 2.5 mm, and 3 mm); (6) concrete compressive strength (30 MPa, 40 MPa, and 50.1 MPa); (7) steel yield stress ( 234.3 MPa, 350 MPa, and 450 MPa). Effects of the variables on the behaviour of the columns are assessed. Failure modes of the columns are also illustrated. It is concluded that the variables have considerable effects on the behaviour of the columns. Moreover, ultimate load capacities of the columns are predicted by the design code EC4, suggested equation of other researchers, and proposed equation of the authors of this paper. The obtained ultimate load capacities from the analyses are compared with the predicted values. It concludes that EC4 gives more conservative predictions than the equations.
Abstract in English:Recently, graphene sheets have shown significant potential for environmental engineering applications such as wastewater treatment. Different non-classical theories have been used for modeling of such nano-sized systems to take account of the effect of small length scale. Among all size-dependent theories, the nonlocal elasticity theory has been commonly used to examine the stability of nano-sized structures. Some research works have been reported about the mechanical behavior of rectangular nanoplates with the consideration of thermal effects. However, in comparison with the rectangular graphene sheets, research works about the nanoplates of circular shape are very limited, especially for the buckling properties with thermal effects. Hence, in this paper, an axisymmetric buckling analysis of circular single-layered graphene sheets (SLGS) is presented by decoupling the nonlocal equations of Eringen theory. Constitutive relations are modified to describe the nonlocal effects. The governing equations are derived using equilibrium equations of the circular plate in polar coordinates. Numerical solutions for buckling loads are computed using Galerkin method. It is shown that nonlocal effects play an important role in the buckling of circular nanoplates. The effects of the small scale on the buckling loads considering various parameters such as the radius of the plate, radius-to-thickness ratio, temperature change and mode numbers are investigated.
Abstract in English:The paper compares and discusses displacement ductility ratios of reinforced concrete walls typically used in one- and two-story houses. Ductility is investigated by assessing response measured on 39 walls tested under shaking table excitations and quasi-static lateral loads. Variables studied were the height-to-length ratio and walls with openings, type of concrete and, steel ratio and type of web reinforcement. An equation to estimate the available ductility of a wall is proposed. Based on statistical analysis of data, values of displacement ductility capacity are recommended. Displacement ductility ratios can be used to compute both strength modification and displacement amplification factors for code-based seismic design.