Sharif Digital Repository

Nowadays functionally graded materials (FGM's) are widely used in different engineering applications such as aerospace, solid mechanics And biomechanics among others. FGM's are inhomogeneous composites made of two different materials, usually a metal and a ceramic with continuous variation of properties. Recently these materials according to their special characteristics are used in micro and nano electro mechanical systems. As size decreases in mechanical systems due to interatomic forces, energy balance law won't be valid locally and therefore classical equations of elasticity may not be used anymore. To overcome this problem,nonlocal theories of elasticity were initiated in works of... 

Free-Space Optical (FSO) communication has received an increasing attention in recent years with its ability to achieve ultra-high data rates (at the order of multiple gigabits per second) over unlicensed optical spectrum. A major degrading factor, particulary in long links is the stmospheric turbulence induced fading. In this thesis, we use spatial diversity and use and make several contributions to the performance analysis of MIMO (Mutli Input-Multi Output) FSO systems. We use MRC(Maximum Ratio Combining),EGC(Equal Gain Combinig),SC(Selection Combinig) and yield significant performance improvments. Finally we import the charectristic of different beamshapes and yields performance... 

The purpose of this project is to model a rotating beam with variable properties of the cross section and also to present an active control method for suppressing the undesired vibrations due to external loading. The beam is modeled as a cantilever Euler-Bernoulli beam with nonuniform physical and geometrical properties. For a practical example, the characteristics of a wind turbine blade was used to solve the problem. The analyzed blade in this study is NREL 5-MW wind turbine blade. But the method can be extended to be used for other blades as well . First the natural frequencies and modeshapes were computed by MATLAB. Then by applying pole placement method, a control strategy was designed... 

Due to tremendous growth in usage of electron beams in different applications like VLSI, welding, chemical processes, Polymer industry and medical applications, precise study of these beams is of great importance. One of the most important parameters in studying electron beams characteristics is the phenomenon and effect of space charge. Although in most methods of analyzing electron optical systems, this effect is neglected, however in high density beams, this effect is bold. Space charge effect is due to interaction and electrostatic repulsion force between each of the electrons in the beam, which results in a change in shape and also divergence of beam. It is worth to mention that in... 

Traditional continuum theory of elasticity becomes remarkably inaccurate in the vicinity of singularities, and when the size eect is of concern. For example in the study of ultra-small objects and ultra-thin lms, near defects, near point of application of a concentrated load and as such, the classical solutions are not reliable. This work focuses on determination of the elastic elds of an edge dislocation near the grain boundary of two perfectly bonded nano-size crystals. It is proposed to study this problem in the context of surface/interface elasticity, and incorporate the eect of the grain boundary on the elastic elds. In contrast to the surface/interface elasticity theory, traditional... 

In this thesis, the formulation of beams and plates in the micro- and nano scales is presented based on the second strain gradient theory (SSGT) introduced by Mindlin. The SSGT is a non-classical continuum theory that includes the second-order gradients of strain tensor in its formulation and this leads to more accurate modeling for mechanical behavior of materials than the strain gradient theory. On the other hand, due to the ever-increasing use of micro- and nano-electromechanical systems, analysis of the mechanical behavior of their deformable components for design and construction is of particular importance. For this purpose, analysis of Timoshenko beams and Euler-bernoulli beams made... 

Thin Walled Beams are widely used in engineering applications with the minimum weight design criteria, ranging from civil to aerospace and many other industrial fields. The weight reduction of the beam leads to importance of the dynamic behavior of the structure. Frequently used thin walled beams have low torsional stiffness and their torsional deformations may be of such magnitudes that it is not adequate to treat the angles of cross section rotation as small. When the vibration amplitudes are moderate or large, the geometric nonlinearity must be included and some new phenomena which do not exist in linear torsional dynamic come into play. Unfortunately, the equations of motion of nonlinear... 

Glass Fiber Reinforced Polymer (GFRP) bars with significant corrosion resistance lead to an improvement in the performance of concrete structures and a significant reduction in costs. High ratio of tensile strength to weight, non-conductive, and non-magnetic properties are other features of GFRP bars. Recent international design standards, such as ACI 440.1R-15 do not recommend including FRP reinforcement in compression, so they replace them by concrete in calculations. The purpose of this study was to investigate the effect of concentric and excentric axial loading on the axial capacity and ductility of GFRP reinforced concrete columns compared to steel reinforced concrete columns,... 

Multiple-Input Multiple-Output (MIMO) communications at millimeter-wave (mm-wave) frequencies (e.g., in the 60 GHz band) is a modern technology recently considered for various applications, such as emerging 5G services for multi-user MIMO (MU-MIMO) and high-resolution frequency-modulated continuous wave (FMCW) MIMO radars to support multi-gigabit throughputs in short-range environments via spatial multiplexing-diversity. Nevertheless, the impairments of communication channels in this frequency band, including significant propagation loss and severe blockage effect, are quite challenging to allow an efficient communication link. Hence, beamforming/beam steering can play a crucial role in 60... 

Nowadays, according to increasing development of construction industry in the world especially in the building area, the need to use technology and innovation for fabrication and maintenance of this industry has increased. And this fact becomes apparent that the use of traditional systems of construction isn’t tailored the countries’ requirements anymore. One of the construction industry’s limitations is the restrictions on architectural designs reys. The columns are among the most important components of structure and have a major role in bearing all gravity and lateral loads and transferring them to the foundation. The failure or destruction of the components in the structure under applied... 

In this thesis an analytical model is applied to the dynamic response of fiber-metal laminate beams subjected to low-velocity impact. By using quasi-static consider-tions, a static model is developed using first order shear deformation beam theory and minimum total potential energy. In the next step, this static model is applied to the one degree of freedom non-linear spring-mass system for developing a model to predict dynamic response of low-velocity impact with the inclusion of material plasticity. By new explicit and simple expression, load-deflection curve, velocity-deflection curve, force-time history and deflection-time history can be derived. By using this analytical approach... 

In this study, epoxy resin has been modified by nano-clay additives using direct mixing method and epoxy-clay nanocomposites were designed and produced with optimized percentage of clay content. By adding the powder of born carbide and lead oxide in nanocomposites new compounds are obtained. The results are used for protection against neutron and gamma rays, respectively. After preparation of epoxy-clay-born carbide and epoxy- clay-lead oxide nanocomposite the effects of irradiation and carbon fiber on mechanical and thermal properties of nanocomposites were examined. The Nanocomposites were exposed to Electron Beam Irradiation (EBI) in 100 and 500 kGy doses to investigate the effect of... 

Shape Memory Polymers (SMPs) are a class of smart materials capable of remembering multiple shapes, and transitioning between them in response to an external stimulus such as thermal or magnetic induction. SMPs have attracted significant attention of both industrial and academic researchers due to their useful and attractive functionality. This thesis aims to analytically develop Euler-Bernoulli, Timoshenko and von Karman theories for beam bending in small strain regime considering SMP constitutive equations. To properly introduce analytical solution for the problem of beam bending, the constitutive model proposed by Baghani et al. (2012) has been used. For this purpose, three dimensional... 

According to key importance of bridges in transportation system vital routes, a need to study and survey of bridges against destructive factors exist. Among these, bridges with concrete deck are widely used. One of the most important factors in destruction of these bridges is steel reinforcements corrosion and destruction of bridge deck. So in order to reduce the aggregation of reinforcements in critical sections and performance improvement of deck beams, a reinforcing substance which is not only resistant against corrosion but benefits from high resistance and stiffness is implemented.In this research the case studied bridge is simulated by finite elements software in two cases; reinforced... 

Performance of reinforced concrete frames is highly dependent on detailing of the joint connections between its members, such as beams and columns. To have a good structural behavior, joints must show ductile behavior and designed based on the philosophy of strong column-weak beam. In the case of sever lacking ductility, strength or even rigidity of the connections, or having a weak column-strong beam, in the existing structures, there is a need for seismic upgrading of the connection. There are several ways for seismic upgrading of this type of connections.In the last decade Fiber Reinforced Polymer (FRP) widely has been used to strengthening the reinforced concrete (RC) members. Most of... 

The flexural behavior of reinforced concrete beams through application of FRP is studied, considering FRP-concrete bonding. Moreover, the nonlinear behavior of concrete (generation of crack and crush) is taken into consideration. Different parameters such as the number of layers of CFRP sheets, the effect of tensile reinforcing bars, the effect of using glass fibers, and modeling resin layer between the concrete and FRP are investigated. The results are compared with the existing experimental tests and those obtained from analytical method, ACI 440.2R-08 and ISIS Canada. The results show that by adding CFRP sheet to the control beam, the stiffness and flexural strength of the beam improves... 

This study deals with the monotonic behavior of reinforced concrete membranes. In the first step, small reinforced concrete membrane panels were studied. Examining the available test results on reinforced concrete panels, a new set of stress-strain relations for normal strength concrete and mild steel bars embedded in concrete. The salient features of the proposed constitutive laws are: 1) considering the effect of reinforcement ratio on average stress-strain relationships of cracked concrete; and 2) considering the gradual reduction of average stiffness of steel bars embedded in concrete. Equilibrium, compatibility, and constitutive relationships were incorporated into an algorithm to... 

The continual deterioration and insufficient strength of reinforced concrete (RC) structures has been a vital problem in the field of civil engineering such an extent that traditional methods of strengthening found to be inconvenient. Nowadays by increasing demands for retrofitting of structures, it necessitates the application of efficient, inexpensive and unobtrusive methods of strengthening. Common way on retrofitting was to use of steel plates externally bonded to RC members. Although this technique has proven to be reasonably effective, it has several distinct disadvantages such as susceptibility of the steel plates to corrode and the excessive weight of steel plates when used in... 

Shear walls are commonly used in tall concrete buildings to resist lateral loads. Due to the presence of regular door or window openings, a shear wall is often divided into smaller wall units coupled together by coupling beams. In any case, the earthquake resistance of a coupled shear wall structure is highly dependent on the nonlinear behaviour, especially the strength and ductility, of the coupling beams. Many existing building structures without provisions for resisting earthquake loads might no longer be considered to be up to the new standard due to increased-load specifications in the seismic code. A large number of RC coupling beams might require rehabilitation or retrofitting to... 

The fiber reinforced polymers (FRP) are widely used for strengthening and rehabilitation of concrete and steel structures. One of the serious collapse mechanisms of the Carbon Fiber Reinforced Polymer (CFRP) strengthened steel beam is due to debonding of the CFRP laminates in the vicinity of high stress concentration regions, such as, at the ends of the laminates. There are several analytical solutions for stress analysis of this effect. Nevertheless, most of these methods are applicable only in the elastic range. In this thesis a simple and efficient analysis modeling will be proposed and investigated for reasonable predicting of the debonding effect. The simplified analytical result will...