• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 87
  • 26
  • 15
  • 5
  • 4
  • 2
  • 2
  • 2
  • 2
  • 1
  • Tagged with
  • 165
  • 76
  • 57
  • 56
  • 45
  • 44
  • 42
  • 40
  • 37
  • 37
  • 35
  • 33
  • 32
  • 32
  • 30
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
61

SPÄNNKABLAR I REAKTORINNESLUTNINGEN : Utredning kring olika konstruktionstyper av Reaktorinneslutningar / Pre-stressed cables in the Reactor Containment : Investigation of different structure types of reactor containments

Al-Mukdadi, Saja, Khaleda, Yeasmeen January 2014 (has links)
Frågor kring kärnkraftverk har alltid varit ett omdiskuterat ämne. Kärnkraftens betydelse varierar stort mellan olika länder. Av 441 reaktorer i världen tillhör 10 av dem till Sverige. Kärnkraftverk i Oskarshamn är en av dem. Företaget OKG har beslutat att genomföra en övergripande utredning kring olika konstruktionstyper av reaktorinneslutningar med detta examensarbete. Arbetet begränsas till att göra en litteraturundersökning. En viss genomgång av både nationella och internationella rapporter har gjorts. Det primära syftet med detta examensarbete är uppdelat i två huvuddelar. Den första delen av utredningen visar olika konstruktionstyper av reaktorinneslutning i hela världen. Den andra delen visar de reaktorinneslutningarna som har en liknande konstruktion som på OKG d.v.s. betong som är förspänd med cementinjekterade spännkablar. En liknande konstruktion finns bl.a. i Finland och Frankrike. Vi har också diskuterat kontroller för andra konstruktionstyper där spännkablarna är omgivna av luft eller fettinjekterade. I utredningen redovisas en del inträffade skador och incidenter i Svenska och utländska kärnkraftverk reaktorer. Företaget har två övriga frågeställningar som undersöktes i senare skedet av arbetsgång. Spännkrafter minskar med tiden på grund av krympning och krypning i spännarmerade konstruktioner vilket påverkar säkerheten av konstruktionen negativt. Som en del av detta arbete utfördes undersökningar om det finns metoder att bestämma spännkrafter där spännkablarna inte är åtkomliga. I det slutliga skedet av utredningen undersöktes metoder som Trafikverket följer för att kontrollera sina broar d.v.s. utföra huvudinspektioner/ besiktningar. Huvudsyftet av examensarbetet har uppfyllts men vissa delar är begränsade på grund av mesta informationer av olika kärnkraftverk är konfidentiella och inte tillgängliga på nätet. Och alla våra undersökningar var webbaserade som innebär att vi hade inte möjlighet att hitta rätt informationer direkt från webben. Samtidigt kontakta de olika utländska kärnkraftverken var inte så lätt på kort varsel. Strålsäkerhetsmyndighet (SSM) hjälpte oss att få kontaktinformation av 3 olika länder. I slutet av rapporten ges analys och diskussion kring utredningen. / Questions regarding Nuclear Power Plants have always been a controversial subject. Nuclear power's importance varies between countries. Of the 441 reactors in the world 10 of them belongs to Sweden. Oskarshamn Nuclear Power Plant is one of them. OKG has decided to conduct a comprehensive investigation of this thesis work around some issues. The main purpose of this thesis work is to make a literature investigation about bracing cables in reactor containment. A specific review of national and international reports has been made and formed a collective basis with the company issues. The introductory part of this thesis is divided into two main parts. The first review of this report considers different structural types of reactor containment in the world. Most nuclear reactors are enclosed by a pre-stressed concrete containment and some have steel reactor containment. In both Sweden and Finland, the enclosure is designed as a concrete cylinder, which is pre-stressed both vertically and horizontally. The second review describes about those reactor containments, which has a similar construction to the OKG (the tendons are placed in the casing that after chucking was injected with cement mortar). A similar construction can be found in Finland and France. The investigation also reveals the damage and accidents in Swedish and foreign nuclear power reactors in recent years. Furthermore, company has two other issues, which were implemented in the later stages of the work. Due to shrinkage and creep in the concrete and relaxation in the tendons, the prestressed capacity decreases with time which affects the structure negatively. The objective of this thesis is to investigate if there are methods for determining tensile forces where the tendons are not accessible. Methods are divided into two different types: one is cement grouting method, same as OKG and another one is oil-injection method. The final review of report is to investigate about TRAFIKVERKET methods to check/inspection the bridges. It can be concluded that the main expectations of this thesis has been fulfilled but some parts are still missing due to limitation of proper information. To contact with the various foreign nuclear power plants was not so easy within this short time. All our experiments were web-based and there were many confidential matters which is unreachable. Swedish Radiation Safety authority (SSM) helped us to get contact details of 3 different countries. The discussions about the reviews are summarized at the end of the report.
62

Distribution of Lateral Forces on Reinforced Masonry Bracing Elements Considering Inelastic Material Behavior - Deformation-Based Matrix Method -

Michel, Kenan 15 June 2021 (has links)
The main goal of CIC-BREL project (Cracked and Inelastic Calculation of BRacing Elements) is to develop an analytical method to distribute horizontal forces on bracing elements, in this case reinforced masonry shear walls, of a building considering the cracked and inelastic state of material. The moment curvature curve of the wall section is created first depending on the section geometry and material properties of both the masonry units and steel reinforcement. This curve will start with an elastic material behavior, then continue in inelastic material behavior where the masonry crushes and the steel start to yield, until the maximum bending moment M_p is reached. Due to reinforced masonry wall ductility, post maximum capacity is also considered assuming a maximum curvature of 0.1%. From the moment curvature curve, the force displacement curve could be extracted depending on the wall height and wall boundary conditions. Matrix formulation has been developed for both elastic and damaged stiffness matrix, considering different boundary conditions. Fixed-fixed boundary condition which usually exists at the middle stories or last story with strong top diaphragm, fixed-pinned which is the case of the last story that has a relatively soft top diaphragm, and pinned-fixed in the first story case. Other boundary conditions could be considered depending on the degree of fixation on the wall both ends at the top and the bottom. The matrix formulation combined with the force-displacement curve which considers different material stages (elastic, inelastic, ductile post peak force) is used to define forces in each bracing element even after elastic behavior. After elastic phase of each wall the stiffness of the element will degrade leading to a less portion of the total lateral force; other elastic walls, i.e., stronger walls, will receive more portion of the total force leading to a redistribution of the total force. This process will be iterated until the total force is distributed on each bracing element depending on the wall section state: elastic, inelastic and ductile post-peak capacity. Flowcharts clearly will show this process. Finally, a Fortran code is developed to show examples using this method. The developed analytical method will be verified by the results of shake table tests held at the University of California in San Diego, USA. Last test performed in the year 2018 uses T-section reinforced masonry walls, subjected to shakings with increased intensity. The total applied force for each shaking could be defined depending on the structural weight and shaking intensity (acceleration). The damage and displacement at each intensity has been recorded and evaluated. Depending on these test results, the results of the analytically developed method will be compared and evaluated. Total system displacement at different lateral load values has been compared for analytical calculations and shake table tests; furthermore, each wall state at increased load has been compared, good agreement could be noticed.:Acknowledgement 5 1. Introduction 7 1.1. State of the Art 9 1.2. Elastic Formulae 9 1.3. Example, Elastic Calculation 12 1.3.1. Stiffnesses of the System 13 1.3.2. Torsion due to Eccentric Lateral Loading 14 1.3.3. Distribution of the Lateral Load on Wall “j” and Floor “i” 15 2. Force Displacement Curve of RM Shear Wall 19 2.1. Introduction 19 2.2. Cantilever Wall 19 2.2.1. Cantilever Elastic Wall 19 2.2.2. Cantilever Inelastic Wall 21 2.2.3. Cantilever Post-Peak Wall 22 2.3. Fixed-Fixed Wall 23 2.3.1. Fixed-Fixed Elastic Wall 23 2.3.2. Fixed-Fixed Inelastic Wall 24 2.3.3. Fixed-Fixed Post-Peak Wall 26 2.4. Moment – Curvature Analysis 26 2.5. Example, Rectangle Cross Section, Cantilever 29 a) Moment Curvature Curve 29 b) Force Displacement Curve 32 2.6. Example, Rectangle Cross Section, Fixed-Fixed 33 a) Moment Curvature Curve 33 b) Force Displacement Curve 33 2.7. Example, T Cross Section, Cantilever 35 a) Moment Curvature Curve 35 b) Force Displacement Curve 41 2.8. Example, T Cross Section, Fixed-Fixed 43 a) Moment Curvature Curve 43 b) Force Displacement Curve 43 3. Matrix Formulation 47 3.1. Procedure 47 3.2. Structure Discretization 47 3.3. Element, i.e.; Wall, Local Stiffness Matrix 48 3.4. Stiffness Matrix of Fixed-Pinned Beam 52 3.4.1. Elastic 52 3.4.2. Pre-Peak Inelastic 54 3.4.3. Post-Peak Inelastic 55 3.4.4. Normal Force Part in the Stiffness Matrix 56 3.5. Stiffness Matrix of Pinned-Fixed Beam 57 3.5.1. Elastic 57 3.5.2. Post-Peak Inelastic 57 3.6. Stiffness Matrix of Fixed-Fixed Beam 58 3.6.1. Elastic 58 3.6.2. Post-Peak Inelastic 60 3.7. Summary of Stiffness Matrices 61 3.7.1. Fixed-Fixed 61 3.7.2. Fixed-Pinned 62 3.7.3. Pinned-Fixed 63 3.8. Transformation Matrix 63 3.9. Assemble the Structure Stiffness Matrix 65 3.10. Assemble the Structure Nodal Vector 66 3.11. Solve, Get Nodal Displacements and Forces 66 4. Matrix Formulation and Deformation Based Method 69 4.1. Elastic Method in Distributing Lateral Force 69 4.2. Elastic and Inelastic Method in Distributing Lateral Force 70 5. Shake Table Tests 73 5.1. Introduction 73 5.2. Design of Test Structure 73 5.3. Material Properties 75 5.4. Tests and Observations 75 5.4.1. Tests up to Mul-90% 76 5.4.2. Tests with Mul-120% 76 5.4.3. Tests with Mul-133% 76 5.5. Deformations 77 6. Verification 81 6.1. T Cross Section, Dimensions, Reinforcement and Materials 81 6.2. Moment Curvature Curve 82 6.3. Force Displacement Curve 85 6.4. Force Displacement Curve of the Structure 88 7. Conclusions and Suggestions 91 8. References 93 Appendix 1, Timoshenko Beam 95 • Fixed-Fixed 95 • Fixed-Pinned 95 • Pinned-Fixed 96 Appendix 2, Bernoulli Beam 97 • Fixed-Fixed 97 • Fixed-Pinned 97 • Pinned-Fixed 98
63

Vícepodlažní administrativní budova / Multi-storey building

Mikulica, Adam Unknown Date (has links)
The purpose of the diploma thesis was to design the supporting structure of an administrative building. The building is located in Brno. The floor plan dimensions of the building are 42.0x42.0 m. The building has 8 floors. The static calculation of the load-bearing structure was developed in two variants. Variant A has a square grid and ceilings arranged in a checkerboard pattern. Variant B has a rectangular growth and the ceilings are arranged in one direction. The ceiling structures and columns of the building are designed as composite reinforced concrete. Drawing documentation is managed for the winning variant.
64

Seismic evaluation and retrofitting of an existing building in Athens using pushover analysis

Lazaris, Angelos January 2019 (has links)
Earthquakes are one of the biggest problems in civil engineering all over the world. Due to earthquakes, great disasters in cities with collapsed structures and human losses have been caused. More specific, old buildings that have been built based on old regulations and design building codes do not fulfil anymore the new criteria of seismic designing.In this study, an old building has been evaluated for the seismic load in order to decide if there is a need for strengthening it using retrofitting methods. The seismic evaluation is based on Eurocode 8 and after the application of retrofitting techniques the building fulfilled its seismic design criteria. The existing building is a four-storey, concrete structure that has been built in 1970 and is located in Athens (the capital city of Greece). The seismic evaluation is conducted by using the software Seismostruct.Two analyses are performed in order to evaluate the seismic behavior of the building. First, an eigenvalue analysis is conducted before and after retrofitting. By using this analysis the torsional sensitivity of the building has been checked. Then, using pushover analysis, the comparison of the target displacement (expected displacement of the building for the design seismic action) for each limit state and the displacement of the building when the first member of the building reached the corresponding limit state, is presented. Target displacement must not be greater than this displacement in order to ensure the safety of the building. If the comparison shows that target displacement is greater, the weak links in the facility should be identified and the proper retrofitting method should be applied for the improvement of the seismic behavior of the building. Pushover analysis is conducted before and after the application of retrofitting methods.After performing the eigenvalue and pushover analysis of the existing building it was found that the building was torsional sensitive and shear failures occurred in many beams of the structure. Regarding the bending failures, the target displacement was not greater than the displacement of the building when the first member of the building reached any of the corresponding limit states. Therefore the building was safe against bending failures. With the application of X-shaped steel braces in selected frames, the building had higher stiffness and it was not torsional sensitive but shear failures occurred again in many beams. Furthermore, compressive failures occurred in columns that were connected with the steel braces. Finally, with the application of fibre reinforced plastic jacketing in the members that failed in the previous pushover analysis there were no shear or compressive failures. Finally the structure was safe against seismic actions.The application of retrofitting methods improved the seismic behavior of the building and the structure fulfilled the updated regulations of Eurocode 8 regarding seismic design. This project thesis may give rise to further studies and researches concerning seismic retrofitting and seismic damage prevention.
65

Design of a Lower Extremity Exoskeleton to Increase Knee ROM during Valgus Bracing for Osteoarthritic Gait

Cao, Jennifer M. 05 1900 (has links)
Knee osteoarthritis (KOA) is the primary cause of chronic immobility in populations over the age of 65. It is a joint degenerative disease in which the articular cartilage in the knee joint wears down over time, leading to symptoms of pain, instability, joint stiffness, and misalignment of the lower extremities. Without intervention, these symptoms gradually worsen over time, decreasing the overall knee range of motion (ROM) and ability to walk. Current clinical interventions include offloading braces, which mechanically realign the lower extremities to alleviate the pain experienced in the medial compartment of the knee joint. Though these braces have proven effective in pain management, studies have shown a significant decrease in knee ROM while using the brace. Concurrently, development of active exoskeletons for rehabilitative gait has increased within recent years in efforts to provide patients with a more effective intervention for dealing with KOA. Though some developed exoskeletons are promising in their efficacy of fostering gait therapy, these devices are heavy, tethered, difficult to control, unavailable to patients, or costly due to the number of complicated components used to manufacture the device. However, the idea that an active component can improve gait therapy for patients motivates this study. This study proposes the design of an adjustable lower extremity exoskeleton which features a single linear actuator adapted onto a commercially available offloading brace. This design hopes to provide patients with pain alleviation from the brace, while also actively driving the knee through flexion and extension. The design and execution of this exoskeleton was accomplished by 3D computer simulation, 3D CAD modeling, and rapid prototyping techniques. The exoskeleton features 3D printed, ABS plastic struts and supports to achieve successful adaptation of the linear actuator to the brace and an electromechanical system with a rechargeable operating capacity of 7 hours. Design validation was completed by running preliminary gait trials of neutral gait (without brace or exoskeleton), offloading brace, and exoskeleton to observe changes between the different gait scenarios. Results from this testing on a single subject show that there was an observed, significant decrease in average knee ROM in the offloading brace trials from the neutral trials and an observed, significant increase in average knee ROM in the exoskeleton trials when compared to the brace trials as hypothesized. Further evaluation must be completed on the clinical efficacy of this device with a larger, and clinically relevant sample size to assess knee ROM, pain while using the device, and overall comfort level. Further development of this design could focus on material assessment, cost analysis, and risk mitigation through failure mode analysis.
66

Optimalt antal stagade spann som krävs för att stomstabilisera en stålkonstruktion : Jämförelse av olika modeller för att hitta den optimala lösningen

Al matar, Leen, Taleb, Mohamad, Abdalnour, Geolle January 2023 (has links)
Purpose: The horizontal stabilization of a building is of great importance in the design of its structural system. Insufficient counteraction of horizontal loads can lead to problems where columns and beams deflect more than the allowable margins. One common horizontal load arises from wind hitting an exterior wall. In this study, four bracing types were analyzed using software to evaluate and compare them, taking various factors into account. The building upon which the study is based is an industrial four-story structure located in Västerås. The building is designed with hinged column bases, which require a stabilization system to maintain its stability. This study aimed to determine the optimal solution for the stabilization system by comparing multiple proposals (X, V, inverted V, and diagonal) considering all factors that significantly influence stabilization. The different proposals were compared in terms of material usage, horizontal displacement, and the number of spans required for steel bracing. Method: Hand calculations were used in this report to design various structural components such as columns, beams, and bracing, which were compared with FEM (Finite Element Method) designs. Additionally, different perspectives were considered within the relevant subject framework, including steel properties, general loads, characteristics, and descriptions of the examined models. Results: After conducting the calculations, it was found that the optimal number of spans required for bracing the industrial steel structure was 32 diagonal braces, placed in the outermost bays on all sides of the building at each floor. This proposal resulted in reduced material usage with a secure horizontal displacement, ensuring stability and durability of the building. Conclusions: In conclusion, this report provides a deep understanding of the importance of stability in buildings, especially when it comes to the safety of occupants and the structural integrity of the building. Proposal 1 has likely met the requirements based on all the calculations and analyzed models that have been conducted, and therefore, diagonal bracing has been chosen as the optimized solution.
67

Prediction of Lateral Restraint Forces in Sloped Z-section Supported Roof Systems Using the Component Stiffness Method

Seek, Michael Walter 04 September 2007 (has links)
Z-sections are widely used as secondary members in metal building roof systems. Lateral restraints are required to maintain the stability of a Z-section roof system and provide resistance to the lateral forces generated by the slope of the roof and the effects due to the rotation of the principal axes of the Z-section relative to the plane of the roof sheathing. The behavior of Z-sections in roof systems is complex as they act in conjunction with the roof sheathing as a system and as a light gage cold formed member, is subject to local cross section deformations. The goal of this research program was to provide a means of predicting lateral restraint forces in Z-section supported roof systems. The research program began with laboratory tests to measure lateral restraint forces in single and multiple span sloped roof systems. A description of the test apparatus and procedure as well as the results of the 40 tests performed is provided in Appendix II. To better understand the need for lateral restraints and to provide a means of testing different variables of the roof system, two types of finite element models were developed and are discussed in detail in appended Paper I. The first finite element model is simplified model that uses frame stiffness elements to represent the purlin and sheathing. This model has been used extensively by previous researchers and modifications were made to improve correlation with test results. The second model is more rigorous and uses shell finite elements to represent the Z-section and sheathing. The shell finite element model was used to develop a calculation procedure referred to as the Component Stiffness Method for predicting the lateral restraint forces in Z-section roof systems. The method uses flexural and torsional mechanics to describe the behavior of the Z-section subject to uniform gravity loads. The forces generated by the system of Z-sections are resisted by the "components" of the system: the lateral restraints, the sheathing and Z-section-to-rafter connection. The mechanics of purlin behavior providing the basis for this method are discussed in appended Paper II. The development of the method and the application of the method to supports restraints and interior restraints are provided in appended papers III, IV and V. / Ph. D.
68

Biomechanical Response of Human Volunteers and Surrogates in a Variety of Loading Regimes

Beeman, Stephanie Marie 08 January 2016 (has links)
Unintentional injuries present a major threat to the health and welfare of humans. Over 120,000 deaths and over 30,000,000 non-fatal injuries are estimated annually in the United States. The leading causes of nonfatal injuries vary with age, but falls, motor vehicle collisions (occupants), and being struck by or against are among the top 4 leading causes of unintentional injury for all ages. The loading mechanism that cause forces to be transmitted to the body during these events can cause a wide assortment of injury types with a range of severities. Understanding the biomechanical response to loading in these environments can facilitate efforts in injury mitigation. Biomechanical responses can be quantified by performing controlled laboratory experiments with human volunteers and surrogates, such as anthropomorphic test devices (ATDs) and post mortem human surrogates (PMHSs). The overall objective of this dissertation is to quantify the biomechanical response to loading regimes present in motor vehicle collisions, falls, and when being struck by or against an object using human volunteers and surrogates. Specifically, the research will achieve the following: quantify the dynamic responses of human volunteers, Hybrid III ATD, and PMHSs in low-speed frontal sled tests; quantify the neck response of human volunteers and PMHSs in low-speed frontal sled tests; quantify the kinetic and kinematic responses of PMHSs and the Hybrid III ATD in high-speed frontal sled tests; characterize thoracic loading as a result of same level falls using a Hybrid III ATD; and quantify the ability of children to swing sword-like toys and the human kinematic response that could be anticipated as a result of forceful impact using a Hybrid III 6-year old head and neck. / Ph. D.
69

Sistema computacional com geração de dados e visualização de resultados para estrutura de edifícios / A computational system with input data generation and output data visualization for building structures

Liserre, Luiz 16 May 2003 (has links)
Este trabalho trata do desenvolvimento de um sistema computacional, para a geração de dados e apresentação de resultados, específico para as estruturas de edifícios. As rotinas desenvolvidas devem trabalhar em conjunto com um sistema computacional para análise de estruturas com base no Método dos Elementos Finitos, contemplando tanto as estruturas de pavimentos; com a utilização de elementos de barra, placa/casca e molas; como as estruturas de contraventamento; com a utilização de elementos de barra tridimensional e recursos especiais como nó mestre e trechos rígidos. A linguagem computacional adotada para a elaboração das rotinas mencionadas é o Object Pascal do DELPHI, um ambiente de programação visual estruturado na programação orientada a objetos do Object Pascal. Essa escolha tem como objetivo, conseguir um sistema computacional onde alterações e adições de funções possam ser realizadas com facilidade, sem que todo o conjunto de programas precise ser analisado e modificado. Por fim, o programa deve servir como um verdadeiro ambiente para análise de estruturas de edifícios, controlando através de uma interface amigável com o usuário uma série de outros programas já desenvolvidos em FORTRAN, como por exemplo o dimensionamento de vigas, pilares, etc. / This work deals with a pre and pos data processing computational system specific for building structures. This computational system has been developed to work together with a finite element program for structural analysis, and it must include elements for flood structures analysis, as bars, plates, membranes and springs; and elements for bracing structures, as 3D-bar and rigid elements. Borland\'s Delphi, a rapid application development environment based on Object Pascal, has been used in this work. The reason for this choice is to provide an easy way to future modifications and additions in the source code. Finally, the developed system should make possible the integration, through user friendly interfaces, with other programs already developed in Fortran, for instance, for designing beams, columns, and others structural elements.
70

Treatment of lower limb spasticity in adults using a multimodal intervention: A mixed-methods approach evaluating the impact across all domains of the ICF

Kim, Jasmine Min Jung 07 May 2014 (has links)
Spasticity is highly prevalent in neurological conditions involving upper motor neuron lesions (UMNL). Lower limb spasticity is known to impair gait and limit participation in physical activity. Multimodal interventions including botulinum toxin A, orthoses, and physiotherapy have shown longer lasting improvements compared to unimodal interventions. Studies to date, however, have not examined the long term efficacy of this multimodal intervention nor have they examined the impact across a breadth of domains necessary to comprehensively and fully understand its impact. The aim of this study was to investigate the efficacy of a multimodal intervention to treat lower limb spasticity in adults using a longitudinal mixed-methods approach, including a comprehensive set of outcome measures spanning the domains of the International Classification of Functioning, Disability and Health (ICF) model. Seven-teen participants with chronic UMNL were included in the analysis as per inclusion criteria and showed improvements at 6 and 12 months, compared to baseline, within all domains of the ICF model. / Graduate / 0571 / 0382 / 0384 / jazkim@uvic.ca

Page generated in 0.0465 seconds