Sharif Digital Repository

Bridges are one of the most important parts of the transportation network and play an important role in relief after earthquakes. Therefore, detecting where and how much damage take place is vital. Bridge structure is consist of two parts: substructure and superstructure. Usually, superstructure remains intact during earthquake because of rigidity and high strength of it. In the other hand, damage localizes to substructure. We also use high safety factor to piles and cap piles so they experience little or no damage. As a result, columns suffer damage more than other parts. In this study, the focus is on columns damage. This study also is limited to non-prestressed multi-cell box girder... 

In this thesis, a new wind turbine scheme based on Electrically-Excited Synchronous Generator (EESG) and diode-bridge rectifier is proposed and developed. This new scheme is mainly based on the idea of generator excitation current employment as a means of wind turbine control. That is why the new scheme is called Excitation Controlled Synchronous Generator (ECSG) wind turbine. The most important aspects of the proposed ECSG wind turbine scheme are cost-effectiveness, simplicity and higher reliability, as well as higher efficiency. Considerable cost reduction for the converter unit of ECSG wind turbine is so important since costly converter has been one of the main challenges of the... 

Integral abutment bridges (IABs) are bridges in which the deck is cast monolithically with abutment backwalls. These bridges are also jointless through deck length, due to which they act as a frame in their longitudinal direction. These differences with common seat-type bridge construction, have made IABs more economical to build and maintain and superior in seismic performance. As such, in various countries, this method of construction have been prescribed whenever possible. As an instance, integral construction is mandatory for bridges up to 60 meters in total length in England. IABs have become more of a geotechnical problem rather than simple structural problem of conventional bridges in... 

Nowadays, because high global demand for energy has led to the extensive use of fossil fuels with numerous unintended consequences such as air pollution and greenhouse effect, research and development around optimization of energy infrastructure has become much more important. Consequently, many scientific approaches have been applied to replace fossil fuels with renewable natural energy resources. One of the renewable energy types that fewer papers have been published about it, is the enormous energy of Marine currents. The origin of this energy is mostly tidal effect, or ocean currents that are available in most of oceans and seas around the planet earth. The most important criteria for... 

With improvement of design and analysis techniques, use of irregular bridges has been expanded. These improve the aesthetics of urban spaces as well as providing shorter highways in impassables. Horizontally curved bridges are among the type of structures, which needs to be designed based on three-dimensional analysis. In this thesis, three-dimensional nonlinear analysis was performed by Endurance Time Method (ET) on horizontally curved bridges. Nonlinear models have been analyzed under ET acceleration functions. Comparing ET results in DBE level with earthquake responses, the difference between these two methods were determined. ET estimated earthquake responses with good accuracy;... 

This thesis targets the multidisciplinary area of time-variant seismic risk analysis of transportation networks. For this purpose, a new methodology and a library of probabilistic models are developed. Risk, in this context, denotes the probability of exceeding the sum of direct and indirect losses due to seismic events. Direct economic losses are due to the repair cost of the physical damage in the components of the network, such as bridges. The indirect losses are due to the reduced capacity of the components for traffic flow, which results in increased travel times in the network. This leads to socioeconomic losses. In this research, a reliability-based approach is adopted to carry out... 

Today, in different industries,as the use of high voltage DC power supplies is increasing, the need of output voltage precision also is increasing. One way to make High DC voltage is to use a multi-output DC-DC converter and makethe output series.Existing problems in measuring high voltages, results in this idea That in these converters, we measure and regulate only one of the outputs and estimate the others by circuit elements. In this estimatin, differences between the transformer parasitic elements are very effectiveon transformer various output voltages. In this thesis after a comprehensive study on the pulse transformer parasitic elements and choose a suitable model for it, the... 

Post-tensioning is the most versatile form of prestressing, a technique which enables engineers to make the most effective use of the material properties of concrete, and so to design structural elements which are strong, slender, and efficient. Design of post-tensioned concrete structures is not difficult and, if done properly can contribute significantly to the economy and the aesthetic qualities of a structure. Post-tensioned building floors and bridge girders have found widespread use in office buildings, parking structures and bridges. They are also frequently employed in warehouses and public buildings. Now a days bridges and other type of structures, in many countries are designed... 

Fault-tolerant ability is more subjected in Cascaded H-Bridge Multilevel Inverter due to its high-power medium-voltage applications and large number of semiconductors switches used in its structure. In this thesis, the goal is performance improvement of Cascaded H-bridge Multilevel Inverter under faulty conditions. Since to achieve the post-fault ability two steps; fault detection and post-fault control are required, both steps are considered in the improving process. In this dissertation, first operation of Cascaded H-Bridge Multilevel Inverter in normal and faulty condition is surveyed. Then, the conventional fault detection methods are mentioned and post-fault control methods are... 

During an earthquake, if the seat width provided at the joint is less than the relative joint opening, the bridge’s superstructure becomes unseat which leads to potential collapse due to the lack of support. Because of the catastrophic consequences of loss of support and the perception that the damage could easily be prevented at relatively low cost, some retrofitting programs focus on preventing such failures involved the addition of longitudinal restrainer cables and bars to limit the relative movements at expansion joints. Noticing the weaknesses of usual restrainers including the transmission of excessive forces to substructures, weak capability of energy dissipation during severe... 

High voltage dc-dc converters are widely used in industrial applications. One of the methods for generating the high voltage is series connection of isolated voltage sources which can be produced by a multiple output converter. One major problem of multiple output converters is their cross regulation. In this project, the operation of a full-bridge based dc-dc converter (FBBC) is investigated in both single output and multiple output cases and analytical expressions for its output voltage and cross regulation are derived. Then, the effect of different parameters of the converter on the cross regulation is studied. It has been shown that increasing the input voltage of the converter improves... 

Three dimensional analyses have been carried out for predicting the behavior of the jointed rock slope of the abutments of the bridge which is proposed to be constructed across the river Karun4 in Iran using 3DEC. The rock sloping at 500 to 600 are composed of highly jointed rock mass and the joint spacing and orientation are varying at different locations. Since 3DEC is a three-dimensional numerical code, utilizes a Lagrangian calculation scheme to model large movements and deformations of a blocky system, allows for modeling of large movements and rotations, including complete detachment of rigid or deformable discrete blocks has been utilized for the analysis. The analysis has been... 

Purpose of this research is to investigate the effects of different seismic isolation techniques and effect of their location on seismic behavior of assymetric bridges and on mitigating their seismic demand. According to different types of isolators and their possible locations, a research is necessary to help to choose the optimum choice among different possible choices for isolators and their location. In this strudy, Lead-Rubber Beraing (LRB), Friction Pendulum Systme (FPS) and High Damping Rubber (HDR) isolators have been investigated and 3D bridge models are 3-span concrete box girder with 50 meters long each span and each interior piers, 7 or 14 meters long. Isolators also can be... 

Following inadequate performance of bridges during the past earthquakes, serious attention has been drawn to evaluation of seismic vulnerability of existing bridges and retrofit measures. This research surveys seismic performance of existing bridges according to the latest manual for seismic rehabilitation of highway bridges in America (FHWA2006). This manual introduces six different methods which vary considerably in sophistication, rigor and applicability. This research is based on method D2 (Nonlinear Static Procedure or Pushover Method) in which the seismic demands are determined by elastic methods such as multi-mode response spectrum, or elastic time history method and capacity... 

In recent years, steel tub girder superstructures have been exceedingly used in long span superstructures due to their significant torsional and flexural stiffnesses. In such superstructures, end diaphragms made of plates are one of the most important members in transferring seismic forces to the substructure. Despite the importance of end diaphragms, limited number of studies have been conducted on their behaviour and as a result, their design procedure is not clear. In this dissertation, different configurations of end diaphragms in elastic steel tub girder superstructures were evaluated using finite element models and the required equations for stiffness and strength were derived.... 

During times, reinforced concrete sturctures might need to be strengthened due to environmental factors, material properties, design errors or changes indesign guidelines.Fibre-reinforced-polymer (FRP)composites are prominentmaterialsfor this purpose. Externally full bonding systemhas been widely used for flexural strengthening of reinforced concrete sturctures with FRP. However, the drawback of using this strengthening system is the high reduction of structure's deformability.In this research, partially bonding system used in finite element modeling of a bridge’s deck to increase deformability compared to full bonding system. Results showed that not only deformability but also load... 

The AASHTO Standard Specification defines diaphragms as a transverse member between girders in order to maintain sectional geometry. Some of the reasons in favor of using a diaphragm are that it prevents the girders from twisting during the process of construction and helps in distributing vertical live loads between girders and transfers lateral loads (wind or earthquake) to supports. It also provides restraint for the lateral-torsional buckling of the girders. While diaphragms at the ends of bridges are called end diaphragms, the diaphragms away from the bridge ends are called intermediate diaphragms. These members are usually made of steel or cast-in-place concrete. Based on their... 

The conventional methods in concrete are usually divided to destructive and nondestructive tests. Among these, nondestructive tests are more preferable because they don’t damage the structure or at least the damage doesn’t significantly affect its performance. According to precision of estimation of concrete conditions, nondestructive tests have different levels. These tests on concrete bridge decks range from chain drag to more developed test like Ground Penetration Radar in concrete The optimum ease of use, cost and the precision of results of Ultrasonic Pulse Velocity (UPV) test compared with other nondestructive methods have made it a most widely used method. The precision of results of... 

Poor maintenance of concrete bridges in the past years in Iran, caused serious damages, so most of them need rehabilitation. The majority of repaired members are exposed to repeated damage because compatibility of repair material to substrate concrete not considered as well as weather and loading conditions. This study attempts to improve the repair achievement and durability of concrete bridges. This investigation contains two phases: preliminary study and experimental phase. Preliminary study attends to detect different types of damages of concrete bridges and their causes along with their propagation. The next part of this study discusses about various types of repair materials. In... 

Gas injection is known as a promising Enhanced Oil Recovery (EOR) method for oil recovery in naturally fractured reservoirs. Gravity drainage is the main production mechanism in such reservoir, which also is affected by molecular diffusion in the case of non-equilibrium gas injection. Formation of liquid bridge in fractures between overlying matrix blocks leads to capillary continuity between blocks and subsequent increase of oil recovery. The aim of this study is to determine the required conditions for formation, stability and fracture capillary pressure of liquid bridge and investigation the role of fracture surface roughness, wettability, oil and gas properties, flow conditions and mass...