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  • 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.
51

Lateral stability of ultra-high performance fiber-reinforced concrete beams with emphasis in transitory phases / Instabilidade lateral de vigas de concreto de ultra-alto desempenho reforçado com fibras com ênfase em fases transitórias

Pablo Augusto Krahl 04 July 2018 (has links)
The development of advanced fiber reinforced cement-based materials to provide higher strength, ductility, and durability, as ultra-high performance fiber-reinforced concrete (UHPFRC), enables the design of precast beams with thin sections and reduced self-weight to meet the required flexural performance. However, such slender elements when subjected to transitory phases, and possibly also in permanent stages, are prone to instability failure. So, the present study aims to provide experimental data and analytical solution for UHPFRC beams during the lifting phase, and studies about the other stages. This type of test is rare and was not reported for UHPFRC beams. For testing, the beams were lifted by inclined cables and subjected to a transversal load applied at midspan to induce lateral instability. The displacements of the beams were monitored with total station equipment. Also, a new analytical solution was proposed to predict the failure load of lifted beams and closed-form analytical solutions to predict the rollover load of beams supported by bearing pads and subjected to different loading conditions. Furthermore, there are limited data that characterizes the constitutive behavior of this material. In this context, the present research also focused on providing such laboratory results for UHPFRC with different fiber contents. Besides, analytical models for damage evolution and stress-strain relationship are proposed and applied in numerical simulations. From the results, the UHPFRC beams failed by instability with a load capacity 3.7 times smaller than the flexural load capacity. Furthermore, the analytical solution for lifting predicted the peak load of the experiment with great accuracy. Also, the proposed equations for beams on bearing pads accurately predicted the experimental results available in the literature. The analytical and experimental rollover loads differed by 4.37% and 13.6% for the two studied cases. From material, the stiffness degradation occurred rapidly in UHPFRC under tensile loading while occurred gradually in compression. Also, fiber content influenced toughness and degradation evolution significantly over the loading cycles. Proposed equations were utilized in the Plastic-Damage model of Abaqus that predicted accurately damage growth and cyclic envelopes during all the phases of the tension, compression, and bending tests. The calibrated numerical model also predicted the experimental results with the UHPFRC beams. / O desenvolvimento de materiais avançados à base de cimento reforçado com fibra para fornecer maior resistência, ductilidade e durabilidade, como o concreto de ultra-alto desempenho reforçado com fibras (UHPFRC), permite o projeto de vigas pré-moldadas com seções esbeltas e peso próprio reduzido que atendem desempenho estrutural requerido. No entanto, esses elementos delgados quando submetidos a fases transitórias e também em serviço são propensos a falhar por instabilidade. Então, o presente estudo tem por objetivo apresentar resultados experimentais e soluções analíticas para vigas de UHPFRC durante a fase de içamento e estudos sobre as outras fases. Este tipo de teste é raro e não foi reportado para vigas de UHPFRC. Para o teste, as vigas foram levantadas por cabos inclinados e submetidas a uma carga concentrada transversal aplicada no meio do vão para induzir a instabilidade lateral. Os deslocamentos das vigas foram monitorados com estação total. Além disso, uma nova solução analítica foi proposta para prever a carga de instabilidade das vigas içadas e soluções analíticas para prever a carga de tombamento de vigas suportadas por aparelho de apoio e submetidas a diferentes condições de carregamento. Além disso, existem poucos resultados experimentais que caracterizam o comportamento constitutivo deste material. Neste contexto, a presente pesquisa também se concentrou em fornecer tais resultados experimentais para UHPFRC com diferentes teores de fibras. Além disso, modelos analíticos para evolução de dano e relação tensão-deformação são propostos e aplicados em simulações numéricas. A partir dos resultados, as vigas em içamento falharam por instabilidade com uma capacidade de carga 3,7 vezes menor que a capacidade à flexão. Além disso, a solução analítica para içamento previu carga máxima do experimento com grande precisão. As equações propostas para vigas sobre aparelhos de apoio previram com precisão os resultados experimentais disponíveis na literatura. As cargas de tombamento analíticas e experimental diferiram em 4,37% e 13,6% para os dois casos estudados. Dos resultados do material, a degradação da rigidez ocorreu de maneira rápida no UHPFRC submetido à tração enquanto ocorreu gradualmente na compressão. O teor de fibras influenciou significativamente a tenacidade e a degradação nos ciclos de carregamento. As equações propostas foram utilizadas em um modelo de Dano acoplado à plasticidade que previu com precisão a evolução do dano e as envoltórias cíclicas durante todas as fases dos testes de tração, compressão e flexão. O modelo numérico calibrado também previu os resultados experimentais das vigas de UHPFRC.
52

Development of a Lightweight Hurricane-Resistant Roof System

Amir Sayyafi, Ehssan 30 March 2017 (has links)
Roofs are the most vulnerable part of the building envelope that often get damaged when subjected to hurricane winds. Damage to the roofs has a devastating impact on the entire structure, including interior losses and service interruptions. This study aimed at the development of a novel light-weight composite flat roof system for industrial, commercial and multi-story residential buildings to withstand Category 5 hurricane wind effects based on the Florida Building Code requirements for hurricane-prone regions, the strictest wind design code in the United States. The proposed roof system is designed as a combination of two advanced materials: ultra-high performance concrete (UHPC), reinforced with high strength steel (HSS). The novel combination of these two materials in a specially designed cross section led to a lightweight low-profile ultra-thin-walled composite roof deck, with only 17 pounds per square foot self-weight, 4-inch overall depth and only ¾-inch thick flanges and webs, with no shear reinforcement or stirrup. Two groups of specimens, single-cell and multi-cell, were fabricated and tested in four-point flexure to determine the ultimate bending capacity and ductility of the system. Each group of specimens included two short-span (9 ft.) samples (due to the laboratory constraints) -- one specimen subjected to positive bending and the other one subjected to negative bending, representing the critical loading conditions including the effects of wind pressures. All specimens exhibited pure flexural failure in a ductile behavior and with no sign of shear failure. Finite element models of laboratory specimens were also developed and calibrated based on experimental data in order to project the performance of the system for larger and more realistic spans. The experimental work and the finite element analyses showed that the proposed roof system with its given section has adequate flexural and shear strength, and also meets serviceability requirements for a 20-foot long span. Moreover, connections for the roof system were proposed, including panel-to-panel connections and roof-to-wall connections. In addition to safety, the other advantages of the proposed roof system in comparison to the equivalent reinforced concrete roofs include a three-fold reduction in self-weight, a three-fold reduction in overall profile height, and a five-fold reduction of steel reinforcement. Together, these advantages may lead to an increased span length beyond what is typically feasible for the conventional reinforced concrete slabs. All these features translate the proposed deck to a sustainable roof system.
53

Behavior of Adjacent Prestressed Concrete Box Beam Bridges Containing Ultra High Performance Concrete (UHPC) Longitudinal Joints

Semendary, Ali A. 13 July 2018 (has links)
No description available.
54

Analysis and Design of Ultra-High-Performance Concrete Shear Key for PrecastPrestressed Concrete Adjacent Box Girder Bridges

Hussein, Husam H. 19 June 2018 (has links)
No description available.

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