Sharif Digital Repository

Various forms of springs are applicable, among which spiral and leaf springs can be named. Definition of leaf springs is conventionally applied to constant-width springs and is consisted of step-like leaves, each leaf having constant width. Leaf springs are largely used in vehicles, where they act as a part of suspension system supporting the weight of the vehicle along with connecting spots axles to the chassis. Springs so installed are capable of handling starting and stopping torques as well as sudden vibrations due to load carrying. Most Conventional method of manufacturing leaf springs is to bend strips of appropriate steel between curved dies, quench the strip while held between the... 

Thermal analysis of concrete arch dams is always an important issue in designig these enormous concrete structures. The reason this issue mainly concerns arch dams and not gravity dams is because of little thickness of arch dams which makes them prone to cracking due to thermal loading. To solve any thermal problem we need boundary conditions. In arch dam case, these boundaries are the temperature of the upstream and downstream face of the dam which, depending on circumstances, can be in touch with water or air. Estimating air temperature is a fairly easy task when you have monthly mean temperatures. The challenging part is defining water temperature in any depth of the reservoir whenever we... 

There is a large, at times contradictory body of investigations relating low back pain and spinal curvature in sagittal plane. The previous studies have not been subject-specified, and they have not considered the active tissues in the models. The mechanical load has a significant impact on the prevalence of low back pain and the geometry of lumbar spine in the sagittal plane is one of the most important characteristics in determining the load sharing of the spine. Thus, it is essential to know how the geometry load affects the load sharing of the lumbar spine. As a matter of fact, the purpose of this project is to know how the geometry of the lumbar spine affects the load sharing. Thus,... 

Metallurgical phenomena modeling help the researchers to understand the influence and contribution of different factors on the alloys properties. One of the most interesting phenomenon is the aging process occuring in age-hardenable alloys like 2xxx aluminium series. A factor which has high impact on aging and there are not proper models for evaluating that, is the contribution of plastic deformation. This factor has contribution not only on the dynamic precipitation (during deformation) but also on the natural aging after plastic deformation. So in this research a model containing the role of plastic deformation on dynamic precipitation and the contribution of dynamic precipitation on total... 

Etiological studies proves the fact that Low Back Pain (LBP) is one of the most expensive and prevalent desease all over the world. This fact illustrates the reqiurment of the special effort in ordet to reducing the pain due to this problem. Finite element modeling of human spine is one the suitable methods to simulate the behavior of human spine in different loading conditions. These conditions could be different daily occupational tasks. There is two general viewpoint toward finite element modeling of human spine. The fisrt method focuses on the detailed geometry and mechanical properties of spine, while the other complexities such as detailed muscle forces are overlooked. The latter... 

Vibrating ring gyroscopes (VRG) as MEMS devices are employed to micro scale systems for determination of the rotation rate and rotation speed of them. It is experimentally approved that micro scale structures behaves differently in comparison to macro scale systems, Therefore higher order continuum theories are required for modeling and analysis of these systems. In addition to that there is no comprehensive investigation on the dynamic performance of ring gyroscopes in the literature, In view of this in the present research the static and dynamic analysis of vibrating ring gyroscopes based on the strain gradient theory and the proposed finite element model of the gyroscope is performed. The... 

Using shear walls as an earthquake resistant system in reinforced concrete structures enjoys prominent position among civil engineers in recent years. As most produced stress and damage occurs at the edges of shear wall under combination of vertical and lateral loads, it is expected that seismic behavior of shear walls can be improved by using boundary element at their edges and considering special reinforcing rules. In this thesis, the effect of boundary element details and parameters on seismic behavior of shear walls has been evaluated by a finite element model. By comparing the results with parameters specified in codes, the modeling parameters and performance levels given for shear... 

Shear wall has been widely used in RC structures due to high initial stiffness and lateral load capacity. Hence, the behavior and effectiveness of retrofitting technique on shear wall are needed to be investigated widely. Among several available techniques for retrofitting RC structures, fiber reinforced polymer (FRP) is quite effective because of its high strength-weight ratio, high resistance to corrosion and easy handling and installation. Several researchers have investigated on the behavior of retrofitted RC members with FRP jackets like columns. However, application of FRP laminates on RC walls has attracted less attention by researchers. In this study a numerical investigation on... 

The flexibility of beam to column connections and its effect on behavior of steel structures is one of the most important problems, which is interesting to engineers and scientists for more than 80 years. Hence many studies conducted on this topic to clarify the behavior of this type of connection. In this work, it is tried to study the behavior of double plate connections, which are welded to the beam web by finite element modeling and mathematical method. A novelty of this thesis is some top trough plate which has been implemented to column under beam flange. Based on finding of this thesis few recommendation can be made related to usage of top trough plate. In brief reduction of... 

The main task of the spine from the mechanical point of view, withstand external loads and allow the upper body movements. Hence, as the chief cause of back pain are mechanical parameters. Inability to directly measure the forces acting on the spine as in vivo, further brings us to the use of computer models in various branches of orthopedic biomechanics leads.
The purpose of this project in the first place) to make a detailed finite element model of the L4-L5 spinal motion but, in the second place) loads imposed on it except move in a certain physical activities, taking into account the forces acting muscles (calculated by a musculoskeletal model is available) under which they operate,... 

The aim of this study is introducing and assessing two torsion-based metallic dampers which are named Torsional Disc and Torsional Cylinder dampers based on their geometry and energy absorption mechanisms. As expected, a steel disc and a steel cylinder are exposed to torsion in the Torsional Disc and Torsional Cylinder dampers respectively, and energy absorption occurs through torsional yielding of those two elements. In the introduction section, a mechanism is introduced to put the dampers under pure torsion so as to yield a desirable performance. The dampers are designed to be placed between Chevron braces and the floor beam, and the pure torsion is exerted, through the mentioned... 

Spine biomechanical models suffers from either simplification in passive disc components modeling (modeling via torsional spring or beam elements) in musculoskeletal (MS) models or shortcomings in detailed muscles modeling (via a simple force and torque vector) in detailed finite element (FE) models. Considering these, that is aimed in this study to develop a hybrid MS-FE model which the calculated muscle forces by a MS model (developed based on geometrical and mechanical properties of FE model) for a desired static posture, being applied to a detailed FE model. Considering the change of discs stiffness in FE model under the applied muscles and gravity forces, the equivalent stiffness in MS... 

This study aims to provide a multiscale model of traumatic brain injury including the three levels of macro, meso, and microscale information. In order to do this, a macroscale voxel-baed model of human head was constructed. The model was designed and generated to include mesoscale tissue information as well as a voxel-based approach to include voxel-based microscale data and to be coupled in a multiscale framework. Next, three different microscale models were constructed. The variations of fractional anisotropy within one standard deviation in the regions (including 60% to 70% of voxels) can change the stiffness of the tissue by up to the considerable amount of 40%. The microscale models... 

In this study, the behavior of box column subjected to constant axial load with cyclic lateral force have been investigated by Finite Element method. The resulf of FE anslysis are in a good agreement with experimental result in predicting of behavior and performance of box column. In order to investigation of behavior uses of some performance indices such as axial shortening, over strength, plastic hinge length, out of plane deformation and rotation capacity. The effect of significant parameter such as axial force to yield strength ratio, flange whidth to thickness ratio of flange, web whith to thickness ratio of web, global slenderness ratio and loading protocol on performance indices have... 

Spinal Column is one of the most important parts of musculoskeletal system. Injuries in this region are so rampant and causing vast expense. Risk factors related to spine injuries included personal related ones such as, age, sex, muscles’ strength and career related ones such as body positions at work place and loads. Since in vivo measurements have many restrictions, developing biomechanical models that simulate the response of a person to given loads and conditions has important role in preventing injuries and improving working conditions. Inputs to current models of the spine are considered to have mean value, therefore muscles’ forces and other outputs of these models have single value... 

Spinal fusion surgery is usually followed by accelerated degenerative changes in the unfused segments above and below the treated segment(s), i.e., adjacent segment disease (ASD). While a number of risk factors for ASD have been suggested, its exact pathogenesis remains to be identified. Finite element (FE) models are indispensable tools to investigate mechanical effects of fusion surgeries on post-fusion changes in the adjacent segment kinematics and kinetics. Existing modeling studies validate only their intact FE model against in vitro data and subsequently simulate post-fusion in vivo conditions. The present study provides a novel approach for the comprehensive validation of a lumbar...