Sharif Digital Repository

”Self-organized criticality” is a conceptual term that has helped us describe cer- tain critical behaviors in nature over the past approximately thirty years. In systems exhibiting this characteristic, critical behavior emerges without the need for external parameter adjustments. The necessary mechanism to observe such phenomena is for the critical point to be a dynamical attractor. Based on this, other phenomena have been proposed in which the critical point is not an attractor; instead, a stable cycle forms around it. This mechanism has led to the emergence of a new concept known as ”self- organized bistability.” The primary model proposed for such a phenomenon is based on a sandpile... 

Sandpile models are the simplest models to study self organized criticality (SOC). In these phenomena, system reaches its critical state and shows power law behavior without fine tuning of any external parameters. In nature, many examples of such phenomena has been observed such as earthquakes, rainfalls and heights of mountains. In SOC systems, always there is an input and an out put of energy. In sandpile models the dissipative sites that play the role of energy dissipation, are usualy put on the boundary. In this study we have considered sandpile models which have dissipative site in the bulk. We have controled the ratio of the dissipative sites to the number of whole sites and have shown... 

Considering the environmental pollution caused by the consumption of fossil fuels, replacing clean and renewable energies instead of fossil fuels has become one of the most critical issues across the world. The use of energy geostructures, especially energy piles, to exchange the heat between the superstructures and the ground is one of the approaches for taking advantage of clean energy. In order to maintain the safety and the serviceability of structures built on energy piles, it is necessary to study the effects of heat exchange between energy piles and the ground on the mechanical behavior of energy piles, as well as the effects of various parameters on the interaction between energy... 

Heat exchanger piles are innovative technologies used to harvest heat from shallow ground. Heat exchanger pile, also known as energy pile, transfers mechanical (structural) loads to the ground while acting as a heat exchanger. Heat extraction in winter and heat rejection during summer changes the pile, pile-soil interaction and the surrounding soil temperature. Therefore, pile temperature increments have been recognized as a new factor of controlling the behavior of energy piles in recent decades. Besides, thermal cyclic loadings may affect the serviceability and geotechnical performance of heat exchanger piles. Physical models provide an affordable experimental medium through which new... 

Energy piles couple the structural support role of conventional piles to the heat exchanger role of shallow geothermal systems for any built environment. So, they are subjected to both mechanical and thermal loads. The use of these piles can be useful in reducing greenhouse gas emissions and reducing fossil fuel consumption. With this in mind, this study is conducted to evaluate the thermomechanical behavior of heat exchanges group piles. For this porpuse, a physical model has been constructed in the Advanced Soil Mechanics Laboratory of the Civil Engineering Department at Sharif University of Technology. In this physical model, four closed-end aluminum pipes with a diameter of 20 mm and a... 

A heat exchanger pile is a pile that is equipped with absorber pipes so that it can exchange heat with the surrounding soil. These piles couple the structural support role of conventional piles to the heat exchanger role of shallow geothermal systems for any built environment. So They are subjected to both mechanical and thermal loads. The use of these piles can be useful in reducing greenhouse gas emissions and reducing fossil fuel consumption. In order to study the thermomechanical behavior of heat exchanger piles, a physical model has been constructed in the Advanced Soil Mechanics Laboratory of the School of Civil Engineering at Sharif University of Technology. In this physical model,... 

Nowadays, pile usage in construction of deep foundations has increased significantly, instead of shallow foundation in areas that shallow foundations doesn’t provide enough bearing capacity and measuring the velocity and acceleration due to pile driving is very important. Because, all responses of building and individuals located near the pile driving site influenced by these three parameters: pile vertical displacement, peak particle acceleration (PPA) and peak particle velocity (PPV). One can estimates these important parameters by numerical analysis of pile driving process in different distances and depths to determining the effect of pile driving. Compared values obtained from numerical... 

Bearing capacity of piles depends on many factors among which geometrical properties of piles, soil type, and strength properties of soil are of great importance. Based on these parameters, several approaches have been developed in order to overcome the uncertainty in the prediction of pile bearing capacity. Studies carried out in this area or research can be divided into two main categories: first, laboratory based approaches, and second, numerically based approaches. The research followed in the present study is based on numerical modeling. In this study, a single pile is initially modeled in the axisymmetric configuration and its bearing capacity is determined. The results of the model... 

The phenomenon of lateral spreading occurs as a consequence of earthquakes induced liquefaction in grounds with mild slopes or ending to an opening. This phenomenon has caused many damages to deep foundations and associated structures. Therefore, it is necessary to study and estimate the forces which may be induced by lateral spreading to these structures. Due to the complex mechanism of the effect of lateral spreading on the piles, various tests have been carried out in the form of shaking table as well as centrifuge tests. According to the results of these tests, the forces applied to the piles are significant and can cause crucial damages to deep foundations. On the other hand, because... 

This study highlights an important distinction between heat transfer mechanism in dry and saturated soil. Soil temperature data recorded during model tests, soil thermal response predicted using finite difference and analytical methods are compared with finite element models. In recent years, due to the industrial development of human societies, the energy consumption has been increased worldwide. On the other hand, the most commonly used energy resources are non-renewable energies. Therefore, governments and industries aimed to develop a technology which provides economical use of renewable energy sources. One of the renewable energy sources is the geothermal energy of the Earth. In this... 

In recent earthquakes piles have been severely damaged due to liquefaction-induced lateral spreading. Liquefaction causes lateral spreading in gently sloped saturated soft granular soils, leading to significant damage in structures and deep foundations. Although in recent years many studies have focused on different aspects of this phenomenon, the complex nature of the dynamic interaction between piles and liquefied soil is not yet fully understood. This potential damages are of high degree of importance in southern and northern coastal areas of Iran where several ports and critical facilities are located. The present study focuses on the behavior of a 2x2 pile group against lateral loads... 

Self-organized critical phenomena are interesting phenomena which are ubiquitous in nature. Examples include mountain ranges , coastlines and also activities in the hu-man's brain. In these processes, without fine-tuning of any external parameter such as the temperature, the system exhibits critical behavior. In other words, the dynamics of the system, drives it towards an state in which long range correlations in space and scaling behaviors can be seen.The first successful model which could characterize such systems was BTW model, introduced by Bak , Tang and Wiesenfeld in 1987. This model, later named Abelian sandpile model, was very simple and because of this simplicity, a large amount of... 

In the countries with offshore oil field, Such as Iran, Offshore platforms are important. Hence seismic analysis of offshore platforms is important. Different methods for seismic assessment of these structures are presented. But these methods has own advantage and disadvantages. (Such as long analysis time and simplified assumptions of linear behavior), but by using Endurance Time method, the method had shown the ability to analyze complex structures, It is hoped that these problems can be resolved. In this study, providing a suitable model of soil and structures of a single pile and then an offshore platform using DEEPSOIL and Open SEES software and performance of these structures at... 

The behavior of pile foundations during earthquakes is one of the most important factors that affect the performance of structures. Therefore, a large number of studies have been performed on the behavior of pile foundations under dynamic loading. A lot of procedures for the analysis and design of piles under earthquake loading have been developed, especially after the earthquakes which took place in 1964 in Niigata and Alaska. They introduced two major mechanisms for the failure of pile foundations in liquefiable grounds: Bending mechanism and buckling mechanism.In this research the focus is the evaluation of pile failure under buckling mechanism. A fully coupled three-dimensional dynamic... 

In recent years, growth of industries has led to consistent increase in energy consumption around the globe. On the other hand, non-renewable energy sources are the most consumed ones in the world. Therefore, governments and companies have tried to introduce budgets to facilitate the use of renewable energy sources and make their use cheaper. One of the renewable energy sources is geothermal energy which one economical way to havest it is thermal energy exchange between the building foundation and the ground. Therfore, thermal piles , by the use of a heat exchanger fluid, transfer the heat on the surface to the ground in warmer seasons and in cold seasons, they transfer the heat from the... 

The behavior of pile foundations under earthquake loading is an important issue that affects the performance of structures. Design procedures have been developed for evaluating pile behavior under earthquake loading; however, the application of these procedures to cases involving liquefiable ground is uncertain. The performance of piles in liquefied soil layers is much more complex than that of non-liquefying soil layers because not only the superstructure and the surrounding soil exert different dynamic loads on pile, but also the stiffness and shear strength of surrounding soil diminishes over time due to both non-linear behavior of soil and pore water pressure generation. In this... 

Lateral spreading due to liquefaction and resulting destruction of buildings is important in Iran because of high seismicity and important infrastructure near south and north coasts of Iran. Lateral spreading is vast lateral movement of sloping ground or level ground ending in an opening like river which is caused by earthquake inducedliquefaction. For considering the effects of lateral spreading during design of deep foundations of structures in a susceptible area, one needs to determine the lateral loads on piles under lateral spreading. Present study investigates the behavior of a 3x3 pile group against lateral loads due to lateral spreading with numerical methods using OpenSees software.... 

Loads from laterally spreading ground have been a major cause of damages to pile foundations in past earthquakes. Analysis of case histories have shown that damages are particularly intense when a nonliquefiable surface crust layer spreads laterally over underling liquefied layers. In this research the effect of lateral spreading due to liquefaction on single piles embede in a gently sloping ground has been investigated. Finite element method using OpenSees is used to model the pile and embedded soil. The soil profile for all models consisted of a nonliquefiable crust layer overlying loose sand with Dr = 30-35% overlying dense sand with Dr = 70-80%. The effect of geometric properties such as... 

Numerous structures which are involved in seismic soil-pile-structure interaction have been damaged، failure in piles or even collapsed that can’t predict. Because of difficult modeling in soil، pile، structure interaction prediction the response of structure is impossible. In this study with using the finite element Abaqus software tries to understand the effect of soil pile structure interaction in structure response. By using the time history of Elcentro، structure with different boundary conditions were analyzed and the response of them were compared. Models have different boundary condition such as fixed base، pile groups and pile raft. Also in this study the effect of mat in... 

In recent earthquakes piles have been severely damaged due to liquefaction-induced lateral spreading. Liquefaction causes lateral spreading in gently sloped saturated soft granular soils, leading to significant damage in structures and deep foundations. Although in recent years many studies have focused on different aspects of this phenomenon, the complex nature of the dynamic interaction between piles and liquefied soil is not yet fully understood. Thus more studies in this regard is inevitable. The present research focuses on the discussion and analysis of two large scale shaking table tests of 2x2 and 3x3 group piles. A three layer soil profile was used for the model, consisting of one...