Abstract in English:Abstract This paper presents a series of results with respect to the mean values of shear, base moment and torsion acting in a building obtained through an experimental wind tunnel study using the standard building proposed by the Commonwealth Advisory Aeronautical Research Council (CAARC) as building reference. In the loading determination, the interference of a neighboring building with similar geometric characteristics to the CAARC was simulated, considering variations of positioning and spacing in relation to the reference building. It was concluded that the presence of the neighboring building increased the mean loads in the reference building for a significant number of directions considered. In the case of the considered deviations and the proposed provisions by this study, it was concluded that the vicinity factor that would contemplate the majority of the results obtained in the tests should increase the wind loads by at least 60% in relation to the values obtained for the building reference considered in isolation.
Abstract in English:Abstract A one dimensional finite element model is presented to assess the effect of position and size of the piezoelectric layer of a hybrid beam. The efficient layerwise (zigzag) theory is used for making the finite element model. The 1D beam element has eight mechanical and a variable number of electrical degrees of freedom. The codes are developed in Matlab based on the FE formulation. The beams are also modelled in 2D planar modelling space as a deformable shell using FE package ABAQUS for comparison of results. An 8-noded piezoelectric quadrilateral element is used for piezo layers and an 8-noded quadrilateral element with reduced integration is used for the elastic layers of hybrid beams for making the finite element mesh in ABAQUS. The accuracy of the used elements are assessed for static response. Cantilever hybrid beams with a piezoelectric layer bonded on top of the elastic substrate are considered for the analysis. The beams are subjected to electromechanical loading. A detailed study is conducted to highlight the influence of positon and size of piezoelectric layer on the deflection profiles, tip deflections and through the thickness distribution of displacements and stresses of hybrid composite/sandwich beams. The shape control using various numbers of piezoelectric patches is also studied. The 1D-FE results are compared with the 2D-FE results.
Abstract in English:Abstract Thermal damage in rock engineering occurs in the air-filled and quasi-vacuum environments of rock mass located near or far from the free surface. Meanwhile, dynamic loads are encountered frequently in engineering practice. In this study, 39 limestone samples are prepared, and a series of laboratory tests, including split Hopkinson pressure bar (SHPB), nuclear magnetic resonance (NMR) and optical microscopy analyses, are conducted to investigate the effects of temperature and the environment on the dynamic mechanical properties of limestone. The results show that the macro-physical and dynamic mechanical properties of limestone after thermal treatment can be divided into two stages by a critical temperature of 450°C, at which the thermal damage factor is 0.71 and 0.75 in the quasi-vacuum and air-filled environments, respectively. In the first stage, with temperatures varying from 25°C to 450°C, the thermal damage due to expansion and fracturing slightly influences the related parameters, except the P-wave velocity. However, in the second stage, with temperatures ranging from 450°C to 900°C, the thermal damage caused by mineral decomposition and hydration leads to a remarkable decrease in the dynamic bearing and anti-deformation capacities. The environment plays a negligible role in the first stage but an important role in the second stage, and the dynamic compressive strength and modulus of samples after thermal treatment in the air-filled environment are much lower than those in the quasi-vacuum environment. Both the temperature and environment of thermal treatment should be considered in engineering practice, especially when the temperature exceeds 450°C.
Abstract in English:Abstract A three-dimensional theoretical model for predicting the maximum force sustained by a flexible line wound around a rigid cylindrical body is developed based on Clebsch-Kirchhoff equilibrium equations, considering its bending rigidity, no sliding, modified non-linear frictional law in terms of stress and an external pressure exerted on the line. Likewise, this model is extended to solve the constraint problem of superposed counter wound helical wires. Results given by 4th order Runge-Kutta numerical algorithm show that, except for the line thickness, the constraint ability grows with an increase of other geometric parameters and external pressure. However, it cannot be significantly enhanced by applying external pressure for large initial forces, especially when there is an initial binormal force.
Abstract in English:Abstract Circular hollow sections are usually used in long-span roof truss systems. One of the typology for connecting elements in such structures involves the flattening of bar ends. This article presents the numerical analysis of a plane truss composed of circular hollow sections, in which diagonal bars have flattened ends. In this sense, a new flattening typology called stiffened flattening is proposed, characterized by a non-flat geometry, with the creation of stiffeners in the lateral edges of the diagonal flattened ends. The diagonal connecting system with the chord members uses connecting plates. The plates are welded to the chords and the diagonals are connected to latter through a single bolt. The numerical analysis using finite elements method was developed in two stages through ANSYS software with the Parametric Design Language (APDL), in which parameters such as geometry, materials, element types, boundary conditions and loads are specified. A non-linear analysis was performed using shell elements on the chords, diagonals, plates and welds, and contact elements between the diagonals with stiffened flattened ends and the connecting plates. Initially, a numerical study of the connecting node and the stiffened flattened end was performed, and the results directed the modeling of the plane truss. The numerical results were calibrated with the experimental truss results in full scale. The numerical result of the plane truss was also compared to a theoretical study, considering the axial load eccentricity applied in the diagonal with stiffened flattened ends. The study was based on the consideration of combined effects of axial force and bending moment provided by the Brazilian standard ABNT NBR 8800:2008. The final results indicate that the numerical model proposed is efficient and has good correlation with the experimental and theoretical results.
Abstract in English:Abstract In recent years, modal analysis has become one of the essential methods for modification and optimization of dynamic characteristics of engineering structures. This is the first published study to identify modal parameters of a complex four-stage centrifugal compressor using Operational Modal Analysis (OMA). Vibrational response was measured continuously with sampling frequency of 44100(Hz) by four noncontact eddy current sensors. Applied loads in actual working condition during compressor’s operation were considered as excitation forces. In this study, modal parameters were extracted and compared using various OMA methods, including Frequency Domain Decomposition (FDD), Enhanced Frequency Domain Decomposition (EFDD) and Stochastic Subspace Identification (SSI). PULSETM commercial software as well as an in-house MATLAB code employed to data analysis. The results show that SSI method has a higher accuracy compared to FDD and EFDD methods. However, FDD shows better results when system damping is low in one of the modes.
Abstract in English:Abstract This paper presents the fundamentals for prediction of a more realistic behavior of planar steel frames with semi-rigid connections under dynamic loading. The majority of the research in this area concentrates on the nonlinear static analysis of frames with semi-rigid connections. Indeed, few studies have contributed to the nonlinear dynamic and vibration analyses of frames. Therefore, this article first describes the frames’ semi-rigid connection behavior under monotonic and cyclic loads, and presents the independent hardening technique adopted to simulate the joint behavior under cyclic excitation. In a finite element context, this paper presents an efficient numerical methodology that is proposed in algorithmic form to obtain the nonlinear transient response of the structural system. The paper also presents, in algorithmic form, a complete description of the adopted connection hysteretic model. Satisfying the equilibrium and compatibility conditions, and assuming only the connection’s rotational deformation due to bending as variable, this work obtains the tangent stiffness and mass matrices of the beam-column element with semi-rigid connections at the ends. The study concludes by verifying and validating the proposed numerical approach using four structural steel systems: a L-frame, a two-story frame, a six-story frame, and a four-bay five-story frame. The analyses show that the hysteresis of the semi-rigid connection has a strong effect on the frames’ responses and is an important source of damping during the structural vibration.
Abstract in English:Abstract Estimation of mode II fracture toughness (KIIC) in composite materials is known as a troublous and crucial problem. Dissipated values of KIIC that are reported in different fracture mechanics references is the evidence of the mentioned claim. This problem can signify the necessity of modification on common test methods and fixtures. The present study focuses on the causes of shear test results scattering in composite materials and presents some solutions in the form of necessary corrections that should be performed on the common test fixtures. Mixed mode I/II fracture limit curves are employed to show that the scattering in test results have strong relation with the creation of a considerable Fracture Process Zone (FPZ). It is shown that common test fixtures are blind in confrontation with FPZ and are not able to active toughening mechanisms in pure mode II, correctly. Therefore, estimation of KIIC with available test fixtures has considerable standard deviation. After that, by employing some structural modifications on common fixtures, a new scheme of a shear fixture is proposed that in addition to include the FPZ effects, prepare suitable condition in order to activate the mode II toughening mechanisms. In this regard, it could be found that by applying these reforms, shear load concentration as well as the accuracy of empirical test and repeatability and reproducibility are enhanced. Furthermore, a 3D finite element method (FEM) was considered as the numerical method in which the Iosipesque and new fixture’s specimens were analyzed by ANSYS software. It was found that by applying major amendments in the new shear test fixture, a remarkable precision in results can be obtained in comparison with the previous Iosipesque one
Abstract in English:Abstract This paper presents a synthesis of a spherical parallel manipulator for a shoulder of a seven-degrees-of-freedom prosthetic human arm using a multi-objective optimization. Three design objectives are considered, namely the workspace, the dexterity, and the actuators torques. The parallel manipulator is modelled considering 13 design parameters in an optimization procedure. Due to the non-linearity of the design problem, genetic algorithms are implemented. The outcomes show that a suitable performance of the manipulator is achieved using the proposed optimization.
Abstract in English:Abstract Dynamic simulation of human eye movements can significantly improve our understanding about the visuomotor system and also may be used for clinical applications. In this study we have developed a 3D finite element model of the eye orbit. The major novel issues which are considered in this work are using dynamic finite element method for properly mass distribution modelling during simulation and active motion simulation by employing muscle activation parameter. In this modelling, extraocular muscles are modelled using a continuum constitutive hyper-elastic energy function. Simulation results of force duction and active motion are presented and compared with the experimental results to verify the accuracy and reliability of the proposed modelling. Then, orbital fat deformation during eye motion is studied through various simulations and compared with experimental results. Finally, the proposed eye model and available experimental data are exploited to investigate more details about eye suspension deformation and extraocular muscles characteristics.