Sharif Digital Repository

In this study, first nano structure powders of Fe3AL / Al2o3 by different percentages of reinforcement phases (10, 20 and 50 percent of volume) based on mechanical milling procedure was created. To do so, iron, Al and iron oxide (hematite) pure powder based on special weight percentages mixed with each other and milled in 20 to 100 hour periods based on two different weights of ball toward powder: 10 and 20. Morphological variations, particles sizes and powder densities, lattice strain and phase variations in different timing periods of mechanical milling process was studied by Scanning Electron Microscopy(SEM) , analyzing apparatus of particles sizes by laser , gaseous picnometer and X-ray... 

In this investigation, nanostructure Fe3Al was produced by mechanical milling initially. Pure iron and aluminum powders were milled with suitable ratio 86Fe-14Al by weight. Milling was done up to 120 h times and with BPR 10 and BPR 20. Morphological changes, powder density and size, phase and structural changes, grain size and lattice strain were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM) and laser particle size analyzer (LPSA). 40 h mechanical alloying with BPR 20 led to the corresponding intermetallic compound, Fe3Al with a nanocrystalline structure. Therefore Fe3Al/ZrO2 micro and nanocomposite powders were synthesized with manufactured by milling of... 

The wind phenomenon has always caused significant damage to structures. Suffering from extensive damage and loss over the years has led researchers to establish the novel science of wind engineering. Wind engineering references introduce wind as an intricate dynamic and random phenomenon and encourage engineers to familiarize themselves with its exact effects on structures by utilizing the latest methods of structural analysis, such as time history analysis. In this research, the idea of a new method for time history analysis of tall buildings against the wind is proposed. In this method, the purpose is to determine the responses of the structure against any wind of any intensity and return... 

The aim of this study is to develop the value-based design approach using the endurance time method as a comprehensive and efficient framework in optimal seismic design of structures. Optimal resource allocation is an interesting and important subject in the seismic design of structures from the theoretical and practical viewpoint. Finding optimal solutions requires the use of a trial and error process that is accompanied by repetitive structural performance evaluation. The seismic design process will be efficient when it provides a comprehensive and reliable estimation of the earthquake effects and be cost-efficient in terms of computational demand. In this regard, the value-based design... 

Seismic base isolation is the most effective method of protecting and strengthening structures against seismic damage caused by large to small earthquakes and aftershocks. Providing damping and energy absorption of the seismic isolation at the structure's base level can significantly reduce the cost of repairing and strengthening the structure in addition to reducing seismic damage. However, besides these advantages, due to their high cost, seismic isolations in major infrastructure projects, hospitals, and crisis management centers should have economic and social justification. In this regard, a value-based seismic design approach can justify this important issue. In recent years of... 

This research has been performed with the aim of gaining familiarity with various types of seismic isolation systems, their unique features and numerous advantages, factors affecting their performance and finally their modelling and design. Despite the advantages of seismic isolation systems as control instruments, but where there is not enough information on the involved parameters in the performance of these systems, there is possibility of unpredictable behavior of the structures. Hence, considering the extent and influence of each parameter involved in the performance of the isolators, a parametric study is performed utilizing the 3D models under multi-directional excitations, using the... 

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... 

Vertical addition of existing buildings provides more living space without the need for more land use. Also adding a story on an existing building is one of the common needs in metropolitans. However, the structure may bear high risk due to vertical addition. This study aims to model conventional concrete structures built in Tehran and then assess and compare the seismic performance of base structure and extended structure. Seismic performance of a system is defined as their efficiency in providing enough safety and reducing the Life-Cycle Cost. For this purpose, seven archetypes as base structures and eight extended structures corresponding to base structures, that had residential... 

Disorders with creating the localized states, which are the states with limited spatial distribution, cause carriers of these states become limited to small part of space and cannot participate in the transport. If energy of these states is near the Fermi energy, the Anderson metal-insulator phase transition occurs. In this thesis,we studied type of disorders and determining their Hamiltonian and by studying definition of localization from different aspects, we attained a better explanation of disorders effects on materials. With studying the localization scaling theory, we ex-amined conditions of localization in different dimensions. Then for determining the green function and therefor the... 

In the field of estimating the expected performance of structures under the excitation of earthquakes of different magnitudes, the Endurance time method has been introduced as a fast method in recent years. What is needed now in this method is to study the assumptions and definitions used in this method, to choose more logical definitions, to unify them, and to prove the statistics of this method in the overlapping and generalizable range of different structures. For this purpose, in this dissertation, different definitions have been evaluated in the process of using the Endurance time method and IDA. The results of different definitions for the target time equivalent to each earthquake... 

Structural optimization has always been one of the concerns of engineers. Usually, engineers decide to optimize the structure with its weight. Nowadays we know that the best solution in weight optimization is not good for the structural damage and performance of the structure due to risk analysis.In this study, using the genetic algorithm to reduce construction cost, Loss and damaged cost and total cost of the structure by calculating structural damage based on FEMA-P58 guidelines according to two types of connections (rigid or hinge) and their elements (beams and columns) in two types of structures 4 and 8 story has been investigated.At each stage of increment in algorithms, first, the...