Sharif Digital Repository

Structural elements are exposed to different types of loading which may cause excessive deformations during their life cycle. These deflections may cause damage to the structure .Therefore; reduction of dynamic response of structures can be achieved by exploiting active control system.
In this research, the dynamic behavior of prestressed Eulthemer Bernollli concrete beam under moving Load, support excitation and multi support excitation, controlled by active tendon is studied.The control algorithm employed in this thesis is closed loop linear classical optimal control with displacement-velocity feedback. R and Q matrices are chosen in order to balance the source energy consumption and... 

The main purpose of this study is the analysis of low velocity impact on the light weight sandwich beams. Some parameters such as weight, failure mode, and impact energy absorption capability are very essential in the design of sandwich beams. The failure mode map is a technique to design sandwich structures, in which no single component is over-designed with respect to other components. In this study, the failure mode map of foam core sandwich beams composed of E-glass/Epoxy and PVC foam is drawn and investigated by an analytical method. For this purpose, displacement relations for bending of a sandwich beam are written using higher order theory. In addition, the sandwich beam is modeled... 

The purpose of this study is to develop the reduced order nonlinear modeling of single cell closed section thin walled composite beams. In this way, global behavior of one dimensional beam under axial load, bending and torsional moment is produced. This model is based on the classical lamination theory, and the nonlinear model is developedby usingthe von-karman strains. In this process the effects of material anisotropy and axial warping are considered. Numerical results are obtained for thin-walledcomposites box beams, addressing the effects of fiber angle and laminate stacking sequence. The nonlinear model is compared with theoretical results of homogeneous beams and the natural... 

In evaluating the damage observed in the structures can be seen that the beam to the wall connection in the walls with openings has severe damage and repair and reconstruction of the beams at the connection is very expensive and difficult. One way to improve seismic behavior and reduce damage in the beams are using steel fibers. Hence in the present study the effect of different fibers in seismic behavior of coupling beams with different length to depth ratio are investigated. The concrete used in the beams of high strength concrete (C60). Therefore, nine model with length to depth ratio of 1.75, 2.25 and 2.75 first without fiber and then with 1.5 and 3 percent made in ABAQUS software. This... 

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 work, is to design a cantilever arm made of functionally graded materials so that the arm has maximum natural frequency and minimum mass. In this work the arm is modeled by Euler-Bernoulli beam theory and properties are assumed to be varying through the thickness. The beam is considered to be made of Aluminum and Alumina as metal and ceramic respectively and Genetic Algorithm method is used for optimization step. Finally using FGMs in atomic force microscopes is proposed as a new application of these materials  

Based on the code specifications, in moment-resisting frames the span-to-depth ratio has to be larger than a minimum value to make sure of adequate plastic hinging at beam-ends. This provision poses a restriction on the use of deep beams with short spans, especially for the framed-tube system in tall buildings. In this thesis, a new energy dissipation method is introduced for moment-resisting frames by modifying the mid-span of the beam by two different methods, resulting in: (i) Perforated Shear Links (PSLs) and (ii) Slit Shear Links (SSLs). The links dissipate energy through shear yielding of the web, weakened by perforation or slitting, respectively. A thorough study is conducted on the... 

external radiation therapy is a methods of cancer treatment or improvement of cancer-related complications. various techniques have been developed for external beam radiation therapy. Among which, Intensity Modulated Radiation Therapy (IMRT), due to its ability to adjust the intensity of radiation beams, has a higher capacity to generate appropriate dose distribution based on tumor size and volume. Intensity Modulated Radiation Therapy is one of the most commonly used procedures of delivering radiation to cancerous tissues, with the aim of reaching the prescripted dose in the target volume while minimizing damage to nearby healthy organs. Two decisions are of fundamental importance: to... 

In this study dynamic response of Timoshenko beam and rectangular Kirchhoff plate under moving mass are investigated. Applying Hamilton’s principle, governing differential equations of beam and plate are derived considering the effect of moving mass. Afterward, a numerical-analytical solution based on eigen function expansion method for analyzing nonuniform beams and plates by means of beams’ and plates’ free vibration modes is presented and convergence of the solution is proved by proving that the governing differential equations of Timoshenko beam and Kirchhoff plates are self adjoint. Modal orthogonality circumstances are discussed due to their important role in eigen function expansion... 

Distributed feedback dye lasers are among the suitable candidates for spectroscopic applications due to their capability of producing widely tunable picosecond pulses in UV-IR region. However, the pulsewidth sensitivity of the laser to pump intensity fluctuations hinders its suitability for precision applications. In this thesis, by utilizing widely used Self Q-Switching model, we showed that if the dye solution is pumped by a narrow (sub-nanosecond) pulse, the laser can operates in the single-pulse output mode with a better stability over a wide range of pump intensity. After that, we used a dynamical model based on the induced polarization and Maxwell equations, where the obtained results... 

In the last decades, noticeable experimental and analytical investigations have been carried out on cast-in-place Reinforced Concrete column to Steel beam (RCS) connections, however rarely have been conducted on the precast RCS. In this reaserch, test results of five half-scale interior precast RCS connections with variable joint configurations are presented. The steel beams were connected to the precast column, using face bearing plates, embedded in the connection zone. The flanges of beams were strengthened with respect to scaled section, in order to increase the load transfer to the joint. All samples were loaded under reversed displacement controlled condition. The failure mode, joint... 

The purpose of this study is aeroelastic stability analysis and nonlinear aeroelastic vibration of composite wing with nonlinear 1D beam model. Wing’s structure modelled as thin-walled composite single box beam in linear and nonlinear conditions. Thin-walled composite box beam developed by classical lamination theory and structural nonlinearity is von karman strain. Unsteady aerodynamic of wing modelled with modified strip theory. Aeroelastic equations of wing obtained from modal expansion (assumed mode) and Hamilton’s Principle. In order to stability analysis of wing, the linear aeroelastic equations in state space must be calculated and so with eigenvalue analysis instability speed will be... 

Study of the structural flexibility of large-scale wind turbine components on aeroelastic performance is important under the existence of critical atmospheric conditions. Prediction and control the critical deformations, identifying maximum local deformation and modeling the forces involved, are required. Aeroelasticity analysis is a suitable method for studying the coupling effects of wind turbine aerodynamics, dynamics and structures. This research has been done by modeling wind turbine components including blades, hub, nacelle and tower, taking into account aerodynamic couplings, dynamics and structures. Considering the large scale of reference wind turbine, nonlinear equations have added... 

Novel two dimensional and three dimensional antenna array geometries for smart antenna application are introduced. MMSE beamforming algorithm, using these arrays, in presence of signal, noise and interferences is implemented. Beamforming approach is used for every type of array assuming uniform and log-normal distributions for the interference amplitudes. Equal volume cylindrical or prism type arrays with circular, hexagonal, triangular, square and star cross sections with equal number of elements are considered for comparison. Novel geometries consisting of rotated cross sections are studied as well. In each case the relative SIR’s are compared in these geometries, showing that the... 

In this study, the linear dynamic response of an inclined FGM Timoshenko beam on linear viscoelastic foundation subjected to a traveling mass with constant and variable velocity is investigated. Timoshenko beam theory and von-karman strain-displacement relations are utilized to model the problem. the FGM beam is made of metal and ceramic and it is assumed that material properties of the beam vary continuously in the thickness direction according to the exponential law and the power-law form. The kelvin-voigt damping model is applied to model the internal damping of the FGM beam. The partial differential equations of motion for the bending rotation of cross-section, longitudinal and... 

In the current study, shape-memory alloys are analysed analytically under mechanical loading. Due to the special properties of these materials, their usage in various applications is rapidly increasing. However, mostly, the numerical methods such as finite-elements methods are employed to model the thermo-mechanical behavior of these materials. Also, due to the complexity of their behavior, there are few analytical solutions for them in the literature. In this research, an analytical approach is proposed to investigate the response of these materials under mechanical loading using a fundamental model which is suitable for modelling their crystalline structure. Given the impact of multiple... 

These days usage of prestressed structures in civil projects are increased significantly. One of these structures is prestressed concrete beam. Considering of such charactristics as failure loads , maximum loads, ductility and occurence and extension of cracks in prestressed concrete beams are interested by civil engineering so in this project we try to investigate the effect of increasing in nonprestressed bars with different arrangements in six specimens.
The load enters in static way on each specimen and supports are simple. Considering the results of experiments, ductility increases significantly because of adding longitude and transverse bars and brittle behavior of speciments... 

In recent years use of concrete filled steel tube column structures has been increased due to their several advantages. In these columns the steel tube provides confinement for the concrete core of the column, so it increases axial strength and flexibility of the concrete core, and prevents spalling of the concrete. On the other hand the concrete core delays the local buckling steel tube and increases its bearing capacity. In addition, these columns have higher stiffness and strength than typical concrete columns due to placement of steel in farthest point of column cross section. The steel tube besides its structural role acts as framework for the concrete core and reduces time and cost of... 

Double angle connections, which are welded to the beam web and bolted to the column flange, are usually used to make hinged or semi-hinged connections. Several models are presented in this study whose geometrical properties are different. The finite element software package is used to develop the finite element analysis of the connections. An analytical method is presented that can be used to determine the behavior and deformation for this type of connection. The correctness of Moment-rotation curves of finite element analysis for each connection has been ascertained by comparison, using analytical technique; and a very good agreement has been obtained  

In Mechanical systems there is always possibility of statical and dynamical following force. These forces are generated due to aerodynamic pressure, temperature gradient, and jet thrusters. In unstabel systems, if the value of this force exceeds a certaim amount the system becomes unstable. This value is called as critical force. In order to analyse these systems, fisrt of all, the governing dynamic equations are obtained by using the Galerkin-Ritz method. Then, by utilising the modal analysis, these equation are uncoupled. And then, the Ito set of equations are derived. By utilising the Lyapanov method, Ito equations are transfered to another state. and using the fokker-planc equation the...