Sharif Digital Repository

The modeling of mechanical behavior of Reinforced concrete Structures has been an important issue in civil engineering. In this thesis, an approach to the numerical modeling of different parts of these structures such as concrete and steel bars was presented. The model is based on damage and plasticity in porous materials. The behavior of steel materials was modeled through Von-Misses plasticity model while the coupling of the Gurson plasticity and a rate dependent damage model based on elastic strains were used for modeling the behavior of concrete materials. The effect of interaction between concrete and steel bar in RC members was considered through an experimental relation in which the... 

Concerning the variety of existing buildings and the diversity in the factors which affect the behaviors of structures, subjected to earthquakes, presenting a definite method for studying their seismic vulnerabilities has not been realized yet. Selecting a method which covers all mentioned necessities is extremely wide and complex. From one side, the capacity of structural system should be determined based on its strength and deformability. On the other hand, the nonlinear behavior of structure should be predicted by selecting the probable effects of earthquake on the region. Then, the force or acceleration which causes damage of structure's components, and the whole structural system,... 

Recent research studies on ductile fracture of metals have shown that the ductile fracture initiation is significantly affected by the stress state. In this study, the effects of the stress invariants as well as the effect of the reverse loading on ductile fracture are considered. To estimate the reduction of load carrying capacity and ductile fracture initiation, a scalar damage expression is proposed. This scalar damage is a function of the accumulated plastic strain, the first stress invariant and the Lode angle. To incorporate the effect of the reverse loading, the accumulated plastic strain is divided into the tension and compression components and each component has a different weight... 

Construction is a vast industry. It is one of the vital and important industries in each country because of high financial turn over, creating many job opportunities and developments. Development has always been a great challenge to the environment due to using much of natural materials and resources. Studies show that construction projects produce the highest amount of waste among other industries. By continuing current situation and increasing rate of production of construction waste, nations and human beings will face a lot of problems in the future. Recently, an increasing attention has been focused worldwide to limit using natural resources in order to conserve the... 

Smoothed particle hydrodynamics (SPH) is a meshfree method, based on Lagrangian formulation of Navier-Stokes equations, in which fluid is discretized to particles. This method is suitable and gives much better results for problems in which other methods have severe difficulties, (e.g., tracking of particles, moving boundaries, and problems with large deformations and, physical discontinuity). No need to follow a regular geometric structure in solution process and simple adaptation and coupling with methods such as finite element, are the positive characteristics of this numerical method. In this work, a systematic study of the processes, which are part of a membrane failure in a... 

Coral reef waters are called rainforest. The importance of coral reef waters is related to their diversity and millions species. According to incremental development of Kish Island, specially the west part of this island contributed to Tourism industry which is affected by dredging, sediment discharge in coastal area, constructing waterfront, the flows close to the beach due to breakwater and eutrophication. This Island includes marine resources and many biodiversity .So the management of marine environment is needed to be considered. Iran as a rich country due to coral reefs is considered as a most valuable marine environment in Persian Gulf. The process of polluting Persian Gulf is... 

In this thesis, employing the definition of an effective configuration in the Continuum Damage-Healing Mechanics (CDHM), mechanical responses of elf-healing materials are investigated. Firstly, a constitutive model is proposed to investigate damage and healing phenomena in concrete materials. In order to consider the different behavior of concretes in tension and compression, a spectral decomposition of the stress is utilized. In addition, employing the Clausius-Duhem inequality and considering the irreversible thermodynamics, conjugate forces of the damage and healing are expressed. The Gibbs potential energy is decomposed into three parts; elastic, damage and healing. In the next section,... 

By developing composites, difficulties of modeling of degradation of properties as stiffness is most considered. The recent advances in the modeling of degradations in stratified composites have led to improved models on all scales. Macro scales methods are good to estimate fracture but not to estimate the failure in micro scale (as microcrack) and moreover, they need many experimental data. Therefore by considering a stratified structure which contains fiber, matrix and intermediate area, mesoscale modeling method is most suitable. In this research Micromechanical Progressive Algorithm (MPA) is used. The method employed is Micromechanic Method of Fracture (MMF). In this work by developing a... 

The present paper proposes a micromechanical damage model for two and three dimensional Representative Volume Element (RVE) with randomly distributed cohesive rough slit-like and penny-shaped micro cracks (Barenblatt-Dugdale type). First, the influence of crack roughness on the crack opening under macro hydrostatic stress state is studied and then the energy release contribution to material damage process is estimated. Considering the fractality of the crack trajectories yields to lower values of the volume crack opening. This will result in lower energy release rate in RVE and higher levels of material resistance. Based on the energy release rate of RVE, the effective material properties... 

In oil industry, increment of drilling mud viscosity is of great importance. Water based polymers are widely use as drilling fluid to achieve this goal. Formation damages can be occurred by invading polymer solution into the formation in different ways such as scale and precipitation. These damages appear in different shapes such as reduction in relative permeability and productivity index reduction. In this study we have proposed, designed and fabricated a novel device, called sand pack, to measure the damage of the reservoir which enable us to calculate relative permeability and recovery factor by means of pressure difference and flow rate. Using this lab-scaled device we have measured... 

Cardiovascular diseases are the major cause of death worldwide. Atherosclerosis is one of the major types of cardiovascular diseases in which fibrous and fatty materials, called plaque, build up inside the artery and cause partial or total occlusion of the artery. Intravascular balloon angioplasty with or without stenting is the most common treatment of this disease. In 2010, approximately 954000 stent implantations were performed in the United States. The major issue associated with stenting is reclosure or renarrowing of the transverse section of the artery termed in-stent restenosis (ISR). Unfortunately, nearly one–third of the patients
who receive stent implantation require further... 

Building weight reducing idea and implementation of Lightweight Structures were always attractive for structural engineering experts, scholars and researchers around the world and its proven effects on improving behavior and reducing the forces acting on the structure, has urged researchers to create new designs. Concrete slabs are of a significant portion of the overall weight of the structure. Nowadays, waffle slabs are a demand for structural designers, as a consequence of architectural design evolution and new building management concepts, in spite of its laborious numerical modeling. The objective of this work was to analyze the adequacy of a design method widely used in the modeling of... 

The primary goal of this thesis is to develop a Fault Tolerant Control (FTC) system for a flexible satellite in presence of actuators fault and failure. The actuators of the satellite are including three magnetorquers and three reaction wheels on each principal axis. At first, the three-degree-of-freedom rotational motion of a rigid satellite with two flexible solar panels is modeled. The flexible panels are modeled through the assumed mode approach by a finite set of bending modal motion. The ordinary differential equations of their generalized coordinates are found using the Lagrange’s equation. Then, the dynamic model is validated by comparing the simulation results of the model to the NX... 

The use of conventional multi-scale models for materials that exhibit softening behavior is not possible due to the phenomenon of localization, because the fundamental assumptions of homogenization are no longer satisfying around the localization region, and therefore the macro-scale results depend on the size of the representative volume element and the macro-scale mesh discretization. Also, if the finite elements mesh be fine enough, the solution does not converge to acceptable physical values. This research concerns the multi-scale study of failure and proposes an appropriate method for computational homogenization of that. The main idea is to apply the enhanced homogenization method to... 

Earthquakes can cause significant economic damage to society. These damages include direct economic damage, ie, the cost incurred by the community to rebuild damaged infrastructure. In addition, damaging the infrastructure, the earthquake reduces the level of infrastructure service, and thus, disrupts the businesses that rely on it. The consequences of such disruptions, such as a decline in the level of productivity and efficiency of firms, or an increase in the rate of unemployment and migration from the community, can cause indirect economic damage to society. The costs incurred to society by disasters can be reduced by adopting appropriate solutions. In many cases, however, the incentives... 

This research develops a probabilistic framework for evaluating community resilience subject to earthquake events by modeling the water distribution system and its prevailing inter- and intra-dependencies with other infrastructure systems of the community. This framework is entitled “Rtx,” which is under continuous development at the Center for Infrastructure Sustainability and Resilience Research (INSURER) at Sharif University of Technology, Tehran, Iran. It quantifies the community resilience by integrating hazard models, risk models, and recovery models within an agent-based simulation. Comprehensive modeling of the water distribution system requires a library of probabilistic models,... 

Highway bridges are one of the key components of transportation network and play a significciant role in the recovery of societies after extreme events such as flood and earthquake. The dysfunction or failure of bridges significantly impacts commerce and services and cause direct and indirect costs. Thus, the recovery of theses components immediately after extreme events is vital issue. In this study, a framework developed to evaluate the life-cycle resilience of bridges using the Endurance Time method. At the first part, the effect of deterioration due to corrosion on the seimic vulnerability and resilience of RC bridge investigated by ET method. To this aim, a procedure described to... 

Single lap-shear (SLS) specimens of 2.54, 6.35 and 12.7 mm long SAC305 solder joints were prepared with three different adherend thicknesses. The fracture force was measured at a shear strain rate of 0.01 s-1 for different geometries in the lap-shear configuration in which mode ІІ loading is established. Elastic-plastic fracture mechanics (EPFM) theory was considered to find the energy dissipated in each case using a finite element model (FEM). The fracture energy was found by cohesive zone modeling (CZM) using pre-defined parameters. Both 2D and 3D models were used to explain the variations of fracture energy by evaluating the effective factors that demonstrated the level of constraints on...