Sharif Digital Repository

The propagation behavior of Love wave in functionally graded magneto-electro-elastic half-spaces with a quadratic variation is addressed. The magneto-electromechanical coupling factor, the dispersion relations, electric potential, magnetic potential and displacement are obtained analytically for both magneto-electrically open and short conditions. The effect of gradient coefficient on phase velocity, group velocity and magneto-electromechanical coupling factor are plotted and discussed. Research on the wave propagation in magneto-electro-elastic materials is still very limited. This work provides us with a theoretical foundation to design and practically apply SAW devices with high... 

In this study, the interaction between thin plate completely bonded to the transversely isotropic halfspace and a concentrated force applied horizontally (Mindlin-type force) are considered. This problem has been solved analytically. This problem is used as sample for thin solid films and surface coating technology, where the surface of solid is covered by thethin plate for increasing its stiffness. Moreover, this problem is a good sample when homogenous solid is subjected to contact loading and can be seen that mechanical properties of material which is near the solid surface varies; consequently, a two-phase solid is created.Because of the influence of noted inhomogeneity, solid is... 

In this study, a new type of metallic yielding damper called Telescopic damper is proposed and analyzed numerically. The damper comprises of three concentric steel tubes connected together by lead shear keys. The relative axial deformation of steel tubes under axial forces results in shear deformation and yielding in lead shear keys and dissipates energy. The inner steel tube has a lock which limits its movement to some certain extent and beyond this limit the outer tube activates. Therefore, a multi-linear force-deformation behavior with two different yield plateaus is expected for the introduced telescopic damper. The multi-level yield plateaus of damper makes it effective in both low and... 

In this study, a new concrete slab stiffened by concrete pedestals and steel cables is introduced. The slab system is studied by employing both analytical and numerical methods. The steel cables are connected to the edges of slab and the concrete pedestals mounted at the bottom face of slab act as the middle supports of cables. The tension force in the cable and its inclination results in upward forces acting at the bottom face of slab. With the aims of classical theory of thin plates and the superposition technique, the problem of a simply supported rectangular slab stiffened by cables is studied analytically. The obtained results are verified by a numerical modelling implemented in SAP2000... 

The parametric study of a new introduced metallic yielding damper called telescopic damper is addressed. The telescopic damper comprises of three concentric steel pipes connected together by lead shear keys. The inner and outer steel pipes are subjected to axial loading which results in the shear yielding of the embedded lead cylinders. The inner steel pipe has a lock which limits its movement to some certain extent and beyond this limit the outer tube activates. Employing ABAQUS software, the behavior of damper under cyclic loading is studied numerically. The finite element model is verified by available results in the literature. The effects of inner and outer steel pipes thickness,... 

In this thesis, static and dynamic analysis of nano beams based on second strain gradient theory is presented. Due to their small sizes, nano electro mechanical devices (NEMS) hold tremendous promise for novel, versatile and very sensitive devices for different applications ranging from actuators, transducers and also mass, force, light and frequency detectors. Therefore accurate modeling and analysis of such devices has an important role in their design and performance improvement. Neglecting the size effect, traditional theory of elasticity can not be suitable to predict mechanical behavior of these systems and so, it should be used non-classical theories which include size dependency... 

In this study the axisymmetric and asymmetric problem of interaction between a transversely isotropic half-space and various rst order shear deformation plate theories including Mindlin, Reissner and Vasil'ev are addressed. In order to improve the accuracy of solution, the surface boundary conditions of the half-space are modied.Moreover, the results compared with the exact solution and the most appropriate result is identied. The displacement Green's functions are obtained for both cases, modied and unmodied boundary conditions which can be expressed in a closed form and a numerically evaluated part. The latter is calculated exploiting Built-in numerical interrelation function of... 

In this study, elastic analysis of a functionally graded full-space with quadratic variations under various types of loading is addressed. The elastic responses of the medium are obtained in closed-form under various types of loading including point load, concentrated moment, distributed patch load of rectangular and circular shape, normal ring load, and concentrated torsion. The displacement fields are derived by virtue of the appropriate Green’s functions corresponding to the FGMs with a quadratic variation of elastic moduli and constant poisons ratio of = 0.25 .For the special case of homogeneous medium, the results are verified with available solutions. Furthermore, effects of degree of... 

In this research, a homogeneous elastic half-space with transversely isotropic behavior, reinforced by an isotropic thin membrane is investigated under static loading with an analytical approach. The membrane is considered as an infinite plane with a thickness of negligible and buried at the arbitrary depth from the surface of the half-space, also its flexural strength is neglected and only the in-plane stiffness is considered for it. The reinforced half-space is investigated under several concentrated and distributed static loads, which are applied to the surface of the half-space or buried at the depth of the membrane. The membrane is first modeled as a three-dimensional elastic layer and... 

The main purpose of this study is Performance Based Analysis of steel bridges equipped with Telescopic Dampers and also to design a suitable damper in order to improve the behavior of the structural system and, consequently, reduce the damage to the structure after the earthquake. Different models of dampers such as Buckling Restrained Braces (BRB’s), Hydraulic Dampers, Viscous Dampers, Shear Panel Dampers, Visco-Elastic Dampers, etc., are used according to their specifications along with Laminated Rubber Bearings (LRB’s) to control the structural behavior of bridge, reduce deck displacement and base shear. The result of this project is the design of a special type of telescopic dampers,... 

Ordinary structures absorb a large amount of input energy by structural elements whereas failure in these elements causes a huge loss in structure and it’s really difficult to repair or unrepairable. Nowadays a wide range of metallic dampers is used in structures as fuse elements. this research evaluates the response of structures that are equipped with a novel steel damper named Telescopic Lead Yield Damper (TLYD) which was introduced by Eskandari in 2018. As TLYD has a different yielding plateau it can tolerate large deformations. In this research firstly this novel damper was introduced and the performance of the damper under cyclic loading was demonstrated. Then a numerical model of 6,... 

In this thesis, three new metallic-yielding dampers for dissipation of energy in structures are introduced and studied. The advantages of dissipation of energy from torsional yielding in comparison to tensile yielding is verified by performing both monotonic and cyclic tests on three aluminum alloys specimens and a mild steel specimen. The experiments confirm that the energy absorption of steel in torsion is much higher than that in tension. Three different mechanisms are introduced to transform the axial movement into the torsional rotation. Each mechanism is studied in details. The first two mechanisms can be mounted at the end of bracings and the third one is installed at the... 

Expanded polystyrene (EPS) products are mostly manufactured as disposable products, designed for a single use after which are recycled or disposed as solid wastes. EPS products are increasingly used specially in form of food containers and packing blocks and most of the time are left in nature without any kind of processing, causing environmental pollution. This project intends to investigate physical characteristics of lighter cement concrete with acceptable compressive strength for non-structural elements, made with different percentages of recycled EPS beads. A group of concrete samples are made by replacing coarse aggregate with equivalent volume of recycled EPS beads. Properties like... 

This research investigates the presence of banana shaped crack in transversely isotropic media under internal pressure and calculates the stress intensity coefficients. In the beginning, the equations of equilibrium, along with the constitutive equations governing the transversely isotropic media and the boundary conditions of the problem, are determined. Then, by using a three-dimensional mapping, the non-centered banana shaped crack is turned into a centered crack. In the following, we solve the problem analytically by using the Fabrikant's potential functions for transversely isotropic environment, and by the method provided by Fabrikant rewriting the boundary conditions in terms of these... 

The propagation of anti-plane surface waves in an inhomogeneous magneto-electro-elastic MEE) half-space with 6mm symmetry is studied. By virtue of both direct and indirect methods, the dispersion relations corresponding to two general cases of material properties variation are obtained. In the first case, it is assumed that all material properties involving MEE properties and density vary similarly in depth. Whereas, the second case considers different variations for MEE properties and density. The non-dispersive shear surface wave velocities pertinent to homogeneous MEE media under eight different surface electromagnetic boundary conditions are obtained as the limiting cases of the current... 

The propagation of love waves in a one-layered piezoelectric medium with slightly curved boundaries of sinusoidal type have been investigated in this study. Because of the widespread use of piezoelectric materials as surface acoustic wave (SAW) devices, sensors, actuators and in vibration control, the study of Love wave propagation in this Medias has been in the forefront of present studies in this era. But there always will be imperfection on surfaces. By employing the Taylor expansion up to the first order and using perturbation technic on the case with no irregularity and solving the problem, it has been found that along with the usual displacement components for stratified boundaries,... 

In this study, flexural vibration of a functionally graded nanotube under an initial stress is investigated. The small scale effect is taken into consideration based on Eringen’s nonlocal elasticity theory. The material properties are assumed to vary exponentially along the depth direction. The complete effect of the initial stress is taken into account in the problem formulation. The governing equations of motion are derived by using the Hamilton’s principle on the basis of the nonlocal Timoshenko beam theory. An analytical solution of the governing equations, for free vibration of a simply-supported nanotube is presented. Numerical results are presented to investigate the effect of the... 

The purpose of this study is to apply the governing equations of the theory of porous media with the concept of volume fractions to calculate the isotropic half-space responses subjected to a surface and asymmetric loading and to compare the responses with Biot’s theory. For this purpose, each of the components is first considered continuous and the equilibrium equations of mass and momentum for the solid and fluid phases based on the mixture theory are expressed. The concept of volume fractions and the effect of interaction between the two phases, distinguish these equations from the equations of the continuum theory. Thus, the governing coupled partial differential equations of the theory... 

This study proposes a new metallic yielding damper for seismic applications. First, considering the damper proposed by curadelli in 2009 a simple lead yielding damper was manufactured to determine its maximum allowable axial deformation showing that it cannot tolerate suitable axial deformations. To solve this problem a telescopic damper with curadelli damper’s descriptions was manufactured and tested which increased the last damper’s allowable deformation 100%. Although new damper’s allowable deformation is twofold the old one, it was not enough for seismic applications. In the next step 6 dampers called lead shear dampers (LSD) with modified lead section were tested. LSD deformation... 

In Former research we determinate elastic response of Brazilian Test of transversely Isotropic material . In Bio-mechanic science surveying mechanical properties and modeling biological organ such as bone , tooth and bio-material such as titanium, zirconium with application in joint replacement is very important . One of method to determine properties of bio-material which mostly has transversely Isotropic behavior is Brazilian Test. Also most rocks has transversely Isotropic behavior, so choosing efficient test is so important. In current issue , load apply in limited area and it is also considered friction in area of jaw loading area .By use of displacement potential function ...