Sharif Digital Repository

The concept of equivalent linearization in which the actual nonlinear system is substituted by an equivalent linear single-degree-of-freedom (SDOF) system is extended to soil-structure systems with elastic and inelastic behaviors. Equivalent linearization is one of the approximate methods widely used to estimate the response of nonlinear structures in seismic performance based design procedures as a basis of Capacity Spectrum method. Period and damping of equivalent linear model should be evaluated in a way to predict the maximum inelastic displacement demand of the structure with sufficient accuracy. In recent years, comprehensive statistical studies have been performed to improve the... 

Soil-structure interaction may have a considerable effect on the response of the superstructure. One of the main steps in analyzing the soil-structure system is determining the soil impedances which vary with frequency. Although it is possible to analyze a dynamic system with complex frequency-dependent property matrices, this cannot be taken into account in most standard general-purpose softwares. In addition, the nonlinear behaviour of the structure can only be studied in time domain. Therefore, in the past two decades efforts have been made to replace the soil media with discrete models having a small number of degrees of freedom (DOFs) and a few springs, dashpots and masses with... 

In this study, the change in friction damper’s optimal slip load in 3-D structures due to soil-structure interaction was evaluated. Using AISC-LRFD code, an 8 story shear building has been designed considering gravitational and equivalent static lateral loads. Then, the changes in friction damper’s optimal slip load due to PGA and soil type variation were studied. In this part two PGAs and two soil types were considered. Seven strong ground motions, recorded on soil types E and D was used for each of the two soil types. After normalizing the PGAs of selected records, these records were used for dynamic time history analyses. In the next step, the soil-structure interaction effect has been... 

Viscoelastic(VE) dampers are among the most practical passive control devices that are used to reduce the seismic-induced response of the structures. In this regard, extensive parametric studies have been conducted so far to investigate the performance of these dampers in reducing the seismic response of the structures under various types of ground motions and site soils. In most of these researches, the effect of soil-structure interaction (SSI) is neglected which is acceptable only for the structures located on stiff soils. In present research, the effect of the soil-structure interaction on the performance of VE dampers in reducing the seismic structural response is investigated. Also,... 

In this research, the effects of Rayleigh waves on the response of typical three-dimensional concrete faced rock-fill dams (CFRDs), considering dam-foundation interaction and spatial variability of earthquake ground motion are investigated. The time history of Loma Prieta earthquake (Gilroy 1 station) is used as input excitation. The dam is considered to be located in a prismatic canyon with trapezoidal cross-section. A substructuring method, in which the unbounded soil is modeled by the scaled boundary finite-element method (SBFEM), is used to obtain scattered motion and interaction forces along the canyon. Non-linear model is used for rock fill... 

The lateral response of a Single Degree of Freedom (SDOF) structural system containing a rigid circular cylindrical liquid tank, under harmonic and earthquake excitations is considered. The governing differential equations of motion for the combined system is derived considering the first three liquid sloshing modes (1,1), (0,1), and (2,1), under horizontal excitation. The system is considered nonlinear due to the convective term of liquid acceleration and the nonlinear surface boundary conditions, both caused by the inertial nonlinearity. The harmonic and seismic response of the system is investigated in the neighborhood of 1:1 and 1:2 internal resonances between the SDOF system and the... 

One of the main issues concerning the irregular building structures is the determination of the critical directions of earthquake input to them that leads to maximum structural response parameters. In applying the seismic excitations to the structures, there is always a critical direction in which the application of seismic loads in those directions, would cause the structural system to experience its maximum responses. Therefore, considering the probability of positioning of the structure’s principal axes in that critical direction, the structure needs to be designed based on the critical seismic induced demands. In this project, the CQC3 method has been used to determine the critical... 

Elevated tanks are typically used to store water for drinking as well as fire fighting purposes. The failure of these critical structures during earthquakes can potentially lead to shortage of drinking water, difficulty in putting out fires, and substantial economical losses. Due to the fact that a large number of water tanks with insufficient seismic resistance were extremely damaged or collapsed during past earthquakes, (e.g. the elevated tank of Rasht in 1989 Gilan's earthquake), the reliability of these structures against failure under seismic loads is of critical concern. Numerous studies have analyzed and investigated the dynamic behavior of fluid storage tanks; however, most of them... 

Soil-structure interaction has significant effect on dynamic behavior of the super structure. This effect is usually investigated in two separate parts, i.e., the Kinematic Interaction effect and the Inertial Interaction effect. The first modifies the input ground motion to the foundation as a result of difference in soil and foundation stiffness. The later, i.e., the II effect, introduces the effect of soil flexibility and radiation of waves into the supporting medium on the response of the structure. These effects are usually considered by introducing a replacement oscillator with modified natural period and damping ratio subjected... 

Various types of tanks are used to store a variety of liquids, drinking water, chemicals, petrochemicals, and liquefied natural gas. Of these, one type is ‘elevated tank’ which is used to provide the required pressure for the water distribution systems rather than satisfying the water demand. Satisfactory performance of tanks during strong ground motions is crucial for modern facilities. Theoritical and experimental investigations of the dynamic behaviour of liquid storage tanks are conducted to seek possible improvments in the design of such tanks to resist earthquakes. The behaviour and performance of a new elevated tank was studied in this work. It was carried out through finite elements... 

Sandwich plates have been used in wide range of aerospace, civil, marine and petroleum applications due to their high stiffness-to-weight ratio and load-carrying capability. In most of practical applications in aerospace, marine and offshore industries, sandwich structures are surrounded by a fluid flow e.g. water and air which causes the significant effects on their design parameters namely natural frequency and buckling load. In the present study, Based on the Kirchhoff-Love theory within von Kármán’s geometric nonlinearity, the nonlinear vibration analysis of multilayered sandwich plates subjected to potential flow (inviscid and incompressible fluids) is presented. Rectangular sandwich... 

Patients with a single ventricle disease who have undergone Fontan surgery have always had long-term complications. These complications include pulmonary artery stiffness and decreased ability to exercise. In fact, due to removal of the right ventricle from the circulatory system, blood pressure and pulsatility inflow to total cavopulmonary connection (TCPC) are reduced following this surgery. Creating waves (radial displacement) on the IVC (Inferior Vena Cava) wall can increase pulmonary flow pulsations. The Objective of this study is to test the effect of induced wave amplitude on the pulmonary flow pulsations at the rest condition. Computational fluid dynamic (CFD) simulations were... 

Coronary arteries often experience tortuosity under internal blood pressure and longitude axial twisting. Arterial tortuosity can enhance the stress concentration on the artery walls. Now if the coronary arteries suffer from atherosclerosis (a common disease among adults) the stress concentration on the tortuous artery plaque will be enhanced as well. Increased stress on the plaque may result in plaque rupture and its consequent damages. This study aims to investigate the stress concentration on the plaques and blood flow patterns within the coronary arteries with plaque. Moreover, the plaque growth was predicted taking into account various geometrical parameters including fibrous cap... 

Due to increased atherosclerosis-caused mortality, identification of its genesis and development is of great importance. Although, key factors of the origin of the disease is still unknown, it is widely believed that cholesterol particle penetration and accumulation in arterial wall is mainly responsible for further wall thickening and decreased rate of blood flow during a gradual progression. To date, various effective components are recognized whose simultaneous consideration would lead to a more accurate approximation of Low Density Lipoprotein (LDL) distribution within the wall. In this research, a multilayer Fluid-Structure Interaction (FSI) model is studied to simulate the penetration... 

The prediction of deposition efficiency of submicron particles in the pulmonary alveoli has received special attention due to its importance for drug delivery systems, and for assessing air pollutants health risks. In this work, the pulmonary alveoli of a healthy human are idealized by a three dimensional honeycomb like configuration and a fluid-structure interaction analysis is performed to study the normal cyclic breathing hydrodynamics. A viscoelastic model is used for the mechanical behavior of alveolar wall tissue. In contrast to previous works in which the inlet flow rate is predefined, in this model a negative pressure is imposed on the outside surface of the alveolus which causes air... 

Atherosclerosis in coronary arteries is one of the most important topics due to its high prevalence and the importance of these arteries for supplying blood to the heart. The morphology of endothelial cells (ECs) is an independent index for determining the atheroprone sites. The ECs show a regular elongated and aligned configuration to the blood flow, at the atheroprotected regions; on the other hand, at the atheroprone regions, the cells have a polygonal, randomly oriented morphology. The thesis intended to propose a method for coronary artery simulation, which is able to determine the atheroprone sites regarding the ECs morphology. In addition, the attempts were made to investigate the... 

Single ventricle anomaly is a congenital heart disease which is characterized by anatomical malformations. The main abnormality that a patient faces is desaturated blood flow, which, without any treatment increases the risk of death. The classical treatment is based on a three stage palliative procedure which should begin from the first few days of patient’s life. The final stage is known as Fontan procedure which directly connects inferior vena-cava to pulmonary arteries without going through the ventricle.This connection is known as Total Cavo Pulmonary Connection (TCPC). After surgery, the single ventricle could supply adequate and saturated systemic blood flow for the body, but TCPC... 

Researchers have done a lot of studies about the use of CFS in blood flow modeling in order to improve the supplementary devices or find mechanical factors which cause artery to be diseased. Blood is a complex rheological fluid, blood flow is a pulastile flow, and blood flow field interacts with the deformable vessel wall. Thus, blood flow modeling like other biological phenomena has its own complexities such as anisotropy, vsicoelasticity, and nonlinearity in stress-strain relationship of vessel wall. To explore the role of hemodynamics in the initiation and progression of stenosis in carotid artery bifurcation, a 3D Computational Fluid Dynamics (CFD) technique is applied. The effect of... 

In this study, the simulation of blood flow through a stenosed coronary artery and a bypass graft are discussed using fluid-structure interaction numerical method. Effects of the geometrical parameters of CABG surgery on hemodynamics have been studied. Investigated hemodynamic variables include shear stress on the vessel wall, the velocity profile in high-risk areas and the pathlines. Lower than 0.5 Pa shear stress on intimal layer of arteries causes the formation of plaque on the wall. Angle of 30 degrees and diameter ratio of bypass to host artery of 1:1 are proposed as the optimum geometry. The distance of the anastomosis from the site of occlusion has no effect on surgery. Also,... 

In this thesis, we consider a system containing fluid equations, structure equations, and equations of these two materials’ common interface in three dimensions and on the regular domains. We suppose that the solid which is described by the Lamé system of linear elasticity, moves inside an incompressible viscous fluid in three dimensions, and the fluid obeys the incompressible Navier-Stokes equations in a time-dependent domain. At the fluid–solid interface, natural conditions are imposed, continuity of the velocities and of the Cauchy stress forces. The fluid and the solid are coupled through these conditions. By this interaction, the fluid deforms the boundary of the solid which in turn...