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Análise experimental da punção em lajes de concreto armado e protendido; Experimental punching shear analysis of reinforced and prestressed concrete slabs

Melges, José Luiz Pinheiro
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 29/03/2001 PT
Relevância na Pesquisa
36.74%
As lajes lisas podem oferecer diversas vantagens quando comparadas ao sistema de lajes, vigas e pilares, sendo, em muitos casos, mais econômicas. O uso da protensão pode oferecer outras vantagens, tais como um melhor controle da fissuração e dos deslocamentos transversais da laje. Como a punção é um dos pontos fracos das lajes lisas protendidas, face à grande esbeltez destas lajes, apresentam-se resultados experimentais de ligações laje-pilar interno, com carregamento concêntrico, com e sem armadura de punção (conectores tipo-pino), com e sem protensão por pós-tração (cabos não aderentes). Os principais aspectos analisados foram as influências da armadura de punção e da protensão na resistência da ligação laje-pilar. Fez-se também uma análise envolvendo a previsão da resistência da ligação, dada por algumas normas e códigos. Observa-se que, de um modo aproximado, a armadura de punção eleva significativamente a resistência do modelo à punção, seja ele de concreto armado ou protendido. Observa-se ainda que, embora diminuindo a taxa de armadura dos modelos de concreto armado, para que se introduzissem as cordoalhas de protensão, os valores experimentais obtidos mostram que a presença da protensão aumentou a resistência da ligação. De um modo geral...

Concreto auto-adensável: caracterização da evolução das propriedades mecânicas e estudo da sua deformabilidade por solicitação mecânica, retração e fluência.; Self-compacting concrete: characterization of the evolution of mechanical properties and study of its deformability under mechanical load, shrinkage and creep.

Marques, Ana Carolina
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 29/04/2011 PT
Relevância na Pesquisa
46.47%
O concreto auto adensável (CAA) é um material novo cujas propriedades mecânicas precisam ser estudadas. Ele apresenta em sua composição maior quantidade de argamassa e agregados graúdos de menores dimensões, que podem torná-lo mais deformável que o concreto convencional. Em contrapartida, o melhor empacotamento das partículas no estado fresco do CAA e a sua maior resistência (para uma mesma relação a/c) pode atuar no sentido oposto. Além disso, os modelos de previsão disponíveis na norma brasileira não levam em consideração os concretos especiais. O objetivo deste trabalho é verificar se modelos de previsão disponíveis na literatura são adequados para prever a fluência e a retração do CAA. Este estudo envolve aspectos de sua caracterização por meio de ensaios em laboratório, de retração, de fluência e de outras propriedades mecânicas como resistência à compressão, resistência á tração e módulo de elasticidade. Para o ensaio de fluência foram avaliadas as influências das condições ambientais (através de corpos de prova mantidos em ambiente controlado e sem controle de umidade e temperatura) e idade de carregamento. A partir dos resultados obtidos experimentalmente, foi feita a sua comparação com os modelos de previsão do ACI...

A interpretação do trabalho em enfermagem no capitalismo financeirizado: um estudo na perspectiva teórica do fluxo tensionado; The nursing work interpretation in financial capitalism: a study in the theoretical perspective of "flux tendu"

Souza, Helton Saragor de
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 09/01/2015 PT
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O objeto deste estudo é o trabalho das categorias da enfermagem sob a organização pós-fordista no capitalismo financeirizado. Associamos a mundialização do capital e a predominância financeira à expansão dos serviços de saúde no Brasil. Nesse sentido, discutimos as características do trabalho coletivo em saúde e das categorias de enfermagem. Abordamos a relação geral e particular do trabalho em saúde e problematizamos a leitura do trabalho em enfermagem nos moldes tayloristas. Os estudos de caso concentram-se em três hospitais localizados Região Metropolitana de São Paulo com gestões distintas: administração pública; administração terceirizada para Organização Social de Saúde (OSS); e administração privada. Nessas unidades, através de etnografia e da realização de entrevistas com os profissionais, caracterizamos o tipo de regime de trabalho pela abordagem do tipo de vínculo empregatício; da remuneração; sobre transferências, promoções e demissões; das características do absenteísmo; da relação com a chefia e da ação coletiva. Estritamente, sobre o processo de trabalho, abordamos o predomínio relacional do ato do cuidado, a influência da tecnologia, os erros procedimentais e a saúde dos trabalhadores. Em nossa visão...

Punção em lajes lisas com pilar de borda protendidas com cordoalhas não aderentes

Oliveira, Marcos Honorato de
Fonte: Universidade de Brasília Publicador: Universidade de Brasília
Tipo: Dissertação
POR
Relevância na Pesquisa
26.56%
Dissertação (mestrado)—Universidade de Brasília, Faculdade de Tecnologia, Departamento de Engenharia Civil e Ambiental, 2008.; Serão apresentados neste trabalho resultados experimentais dos ensaios de oito modelos locais de ligação laje/pilar de borda. Este trabalho faz parte da primeira série de ensaios da tese de doutorado de Helder Pontes Gomes na Universidade de Brasília, no ano de 2008. Buscou-se por meio desses ensaios avaliar a influência da relação do momento fletor dividido pela força cortante (M/V), da relação c/d, da presença de overhang em alguns dos modelos e do nível de protensão na resistência à punção para o cálculo da ligação laje/pilar de borda de lajes protendidas. Foram realizadas também comparações entre os resultados experimentais e as previsões analíticas estabelecidas pela NBR 6118:2003 e por algumas normas internacionais de referência, como o ACI 318M-02 e o EUROCODE 2:2001, para então verificar se as formulações preconizadas pelas normas acima são convenientes. Algumas das análises realizadas indicaram que o acréscimo de tensão nos cabos está diretamente associado ao tipo de carregamento aplicado. As deformações sofridas pelo concreto tiveram influência da disposição dos cabos de protensão. A presença de overhang aumenta a rigidez da ligação...

Puncionamento em lajes lisas protendidas com pilares de extremidade e momentos desbalanceados nas duas direções

Gomes, Helder Pontes
Fonte: Universidade de Brasília Publicador: Universidade de Brasília
Tipo: Tese
POR
Relevância na Pesquisa
26.18%
Tese (doutorado)—Universidade de Brasília, Faculdade de Tecnologia, Departamento de Engenharia Civil e Ambiental, 2010.; São apresentados neste trabalho resultados experimentais dos ensaios de dezesseis modelos locais de ligação laje lisa protendida-pilar de extremidade. Buscou-se por meio desses ensaios avaliar a influência da relação do momento fletor M/V (momento fletor nas duas direções ortogonais dividido pela força cortante), da relação C1/d (dimensão perpendicular do pilar dividia pela altura útil da laje), da presença de overhang e do nível de protensão na resistência à punção. Foram realizadas também comparações entre os resultados experimentais e as previsões da NBR 6118:2003 e de outras duas normas: ACI 318M-02 e EUROCODE 2:2001. As análises realizadas indicaram que o acréscimo de tensão nos cabos está associado ao tipo de carregamento aplicado. As deformações das barras da armadura passiva foram bastante influenciadas pelo tipo de carregamento, embora esta influência tenha se concentrado nas faixas do pilar, mais precisamente na região próxima a este. As deformações da superfície inferior das lajes dos modelos sofreram influência da disposição dos cabos de protensão. A presença de overhang aumenta a rigidez da ligação...

Active CFRP-based confinement strategies for RC columns with rectangular cross sections

Agante, Marta A. B.; Júlio, Eduardo; Barros, Joaquim A. O.; Santos, João M. C.
Fonte: Ci-Premier Publicador: Ci-Premier
Tipo: Conferência ou Objeto de Conferência
Publicado em /08/2008 ENG
Relevância na Pesquisa
26.27%
FRP wrapping is a strengthening technique for RC columns mostly used when a significant confinement increase is required. This technique is extremely effective in the case of circular cross-sections, but of marginally effectiveness for rectangular cross-sections columns. The use of post-tensioned CFRP jackets was an attempt to improve the confinement effectiveness for rectangular RC columns, but the level of success has been quite limited. This paper analyzes the viability of using an expansive resin to introduce some level of post-tension in CFRP jacket. In a first step, the optimal percentage of water added to trigger the resin expansion was analyzed. Using the obtained optimal value of water, the influence on the level of jacket post-tension of the width of the gap between the concrete surface and the CFRP jacket was investigated, and its timedependent sensitivity was assessed. Finally, the compression behaviour of specimens confined with this technique was assessed by performing experimental tests. The obtained results revealed that the adopted expansive resin is not an effective technique to assure high levels of post-tension in CFRP jackets for the concrete confinement.

Precast concrete wall-foundation connection. Development of a seismic dissipative connection

Marreiros, Rui Pedro César
Fonte: Universidade Nova de Lisboa Publicador: Universidade Nova de Lisboa
Tipo: Tese de Doutorado
Publicado em /10/2014 ENG
Relevância na Pesquisa
26.68%
Seismic events are a major factor to consider in structural design of buildings in many countries. With the purpose of saving lives, most of the design codes lead to structural solutions that withstand large seismic actions without collapsing, but without taking into account a possible usage of the structures after the earthquake. As a result, it is necessary to consider the time needed to repair/retrofit the damaged structures (i.e. the downtime) since this period of inactivity may result in huge financial implications for the occupants of the buildings. In order to minimise the damages and simplify repair operations, structural solutions with rocking systems and negligible residual displacements have been developed during the last two decades. Systems with precast concrete rocking walls were studied with the aim of investigat- ing suitable and convenient structural alternatives to minimise the damage in case of an earthquake. Experimental, numerical and analytical analyses on post-tensioned solutions, with and without energy dissipation devices, were carried out in this research. The energy dissipation devices were made from steel angles that were further developed during the research. Different solutions for these devices were experimentally tested under cyclic loading and the results are presented. Numerical and analytical work on steel angles was also carried out. Regarding the concrete rocking wall systems...

A numerical study on seismic response of self-centring precast segmental columns at different post-tensioning forces

Nikbakht,Ehsan; Rashid,Khalim; Hejazi,Farzad; Osman,Siti A.
Fonte: Associação Brasileira de Ciências Mecânicas Publicador: Associação Brasileira de Ciências Mecânicas
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/10/2014 EN
Relevância na Pesquisa
46.77%
Precast bridge columns have shown increasing demand over the past few years due to the advantages of such columns when compared against conventional bridge columns, particularly due to the fact that precast bridge columns can be constructed off site and erected in a short period of time. The present study analytically investigates the behaviour of self-centring precast segmental bridge columns under nonlinear-static and pseudo-dynamic loading at different prestressing strand levels. Self-centring segmental columns are composed of prefabricated reinforced concrete segments which are connected by central post-tensioning (PT) strands. The present study develops a three dimensional (3D) nonlinear finite element model for hybrid post-tensioned precast segmental bridge columns. The model is subjected to constant axial loading and lateral reverse cyclic loading. The lateral force displacement results of the analysed columns show good agreement with the experimental response of the columns. Bonded post-tensioned segmental columns at 25%, 40% and 70% prestressing strand stress levels are analysed and compared with an emulative monolithic conventional column. The columns with a higher initial prestressing strand levels show greater initial stiffness and strength but show higher stiffness reduction at large drifts. In the time-history analysis...

The role of substrate pre-stretch in post-wrinkling bifurcations

Auguste, Anesia; Jin, Lihua; Suo, Zhigang; Hayward, Ryan C.
Fonte: Royal Society of Chemistry (RSC) Publicador: Royal Society of Chemistry (RSC)
Tipo: Artigo de Revista Científica
EN_US
Relevância na Pesquisa
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When a stiff film on a soft substrate is compressed, the surface of the film forms wrinkles, with tunable wavelengths and amplitudes that enable a variety of applications. As the compressive strain increases, the film undergoes post-wrinkling bifurcations, leading to period doubling and eventually to formation of localized folds or ridges. Here we study the post-wrinkling bifurcations in films on pre-stretched substrates. Through a combination of experiments and simulations, we demonstrate that pre-stretched substrates not only show substantial shifts in the critical strain for the onset of post-wrinkling bifurcations, but also exhibit qualitatively different post-wrinkled states. In particular, we report on the stabilization of wrinkles in films on pre-tensioned substrates and the emergence of ‘chaotic’ morphologies in films on pre-compressed substrates.; Engineering and Applied Sciences

Simulación Digital como Herramienta para la Gestión del Conocimiento en la Construcción de Edificaciones en Concreto

Orozco Ovalle, Alfonso Rafael
Fonte: Pontifícia Universidade Javeriana Publicador: Pontifícia Universidade Javeriana
Tipo: bachelorThesis; Trabajo de Grado Pregrado Formato: pdf
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Actualmente, quienes ejecutan proyectos de construcción se ven enfrentados a situaciones que generan pérdidas y atrasos en estas. Por esto, es un reto permanente la búsqueda de aumentar la productividad en construcción y la optimización de los recursos en esta, lo cual ha sido confrontado de muchas maneras dentro de las cuales se encuentra la utilización de herramientas computacionales. En este trabajo se elaboran modelos de simulación digital con información real proveniente de un módulo programable y autónomo para captura de fotografías digitales de los procesos involucrados en la construcción de losas en concreto postensado. A partir de estas fotografías junto con información adicional obtenida en campo, se caracterizan los procesos constructivos, teniendo en cuenta el flujo de actividades, la disposición de los recursos humanos en obra y duraciones de actividades. Esta información fue el punto de partida para elaborar el modelo de simulación digital a través del software Arena 14, que representa el procedimiento real de cómo se ejecutó en obra, y en el cual fue posible analizar la disposición de la mano de obra a lo largo del proceso, factores generadores de demoras, esperas y duraciones de las actividades involucradas. Adicionalmente...

Shelf Life and the Effects of Storage Conditions on Post-Tensioned Grouts

Brunner, Brett W
Fonte: University of Florida; University of Florida ( [Gainesville, Fla.] ) Publicador: University of Florida; University of Florida ( [Gainesville, Fla.] )
Tipo: Artigo de Revista Científica Formato: 1 online resource (130 p.)
Publicado em //2014 ENGLISH
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In the series University of Florida Digital Collections.; Includes vita.; (Bibliography) Includes bibliographical references.; (Source of Description) Description based on online resource; title from PDF title page.; (Source of Description) This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.; (Statement of Responsibility) by Brett W Brunner.; (Thesis) Thesis (M.E.)--University of Florida, 2014.; (Local) Adviser: HAMILTON,HOMER ROBERT,III.; (Local) Co-adviser: FERRARO,CHRISTOPHER CHARLES.

Deformation Capacity and Moment Redistribution of Partially Prestressed Concrete Beams

Rebentrost, Mark
Fonte: Universidade de Adelaide Publicador: Universidade de Adelaide
Tipo: Tese de Doutorado Formato: 5564067 bytes; 196399 bytes; 9596673 bytes; 3946117 bytes; 2543466 bytes; 126665 bytes; application/pdf; application/pdf; application/pdf; application/pdf; application/pdf; application/pdf
Publicado em //2004 EN
Relevância na Pesquisa
46.81%
Ductility is a measure of the ability of a material, section, structural element or structural system to sustain deformations prior to collapse without substantial loss of resistance. The Australian design standard, AS 3600, imposes minimum ductility requirements on structural concrete members to try to prevent premature non-ductile failure and hence to ensure adequate strength and ductile-type collapse with large deflections. The requirements also enable members to resist imposed deformation due to differential settlement, time effects on the concrete and temperature effects, whilst ensuring sufficient carrying capacity and a safe design. Current AS 3600 requirements allow a limited increase or reduction in elastically determined bending moments in critical regions of indeterminate beams, accommodating their ability to redistribute moment from highly stressed regions to other parts of the beam. Design moment redistribution limits and ductility requirements in AS 3600 for bonded partially prestressed beams are a simple extension of the requirements for reinforced members. The possibility of premature non-ductile failure occurring by fracture of the reinforcement or prestressing steel in partially prestressed members has not adequately addressed. The aim of this research is to investigate the overload behaviour and deformation capacity of bonded post-tensioned beams. The current ductility requirements and design moment redistribution limits according to AS 3600 are tested to ensure designs are both safe and economical. A local flexural deformation model based on the discrete cracked block approach is developed to predict the deformation capacity of high moment regions. The model predicts behaviour from an initial uncracked state through progressive crack development into yielding and collapse. Local deformations are considered in the model using non-linear material laws and local slip behaviour between steel and concrete interfaces...

Prediction of deformations in post-tensioned prestressed suspended slabs in tall buildings.

Vincent, Thomas J.
Fonte: Universidade de Adelaide Publicador: Universidade de Adelaide
Tipo: Tese de Doutorado
Publicado em //2009
Relevância na Pesquisa
66.81%
The research presented in this thesis focuses on the accuracy of predicting deflections and cambers in partially prestressed suspended slabs. Precision in predicting this behaviour accurately is complex due to the large number of variables which affect the behaviour of suspended prestressed slabs. This level of complexity is particularly relevant for post tensioned slabs due to the numerous on site construction steps. Many of the variables are hard to determine accurately due to their tendency to be unique for each construction site. Variables such as ambient temperatures, concrete material properties, stressing times, applied loads, loading times, prop movement and humidity are all examples of these properties. Hence, when predicting the behaviour of post tensioned suspended slabs of a multi storey building there always remains a degree of uncertainty. The research presented in this thesis addresses crucial areas of this topic and ultimately aims to supply reinforced concrete designers and constructors with additional confidence when predicting this behaviour. The requirement for this project surfaced during the design stages of 151 Pirie, a multistorey building constructed in Adelaide, Australia. The design project for 151 Pirie was particularly complex due to a very ambitious construction timeline. The strict construction timeline was imposed due to the contractual agreement of early occupancy of the top three floors (of a 9 storey building). The client purchasing the top floors required functioning office space within a matter of months. This contract created a construction priority of erecting the bare structural requirements up to and including the top three floors in the shortest possible time. Fittings and services to the top three floors was then the secondary priority. Fitting and services to the lower floors (which would usually be achieved before the upper floors) would be performed at a later date. Excessive deflection limits of the slabs due to the accelerated construction were a major concern for the client. The effect on the deformation performance due to the accelerated construction was difficult to predict for the designer. Therefore...

The generic simulation of reinforced concrete beams with prestressing and external reinforcement.

Knight, Daniel
Fonte: Universidade de Adelaide Publicador: Universidade de Adelaide
Tipo: Tese de Doutorado
Publicado em //2014
Relevância na Pesquisa
26.62%
This thesis presents a series of journal papers in which a new segmental moment-rotation (M/Ө) approach is developed for simulating the instantaneous and sustained loading behaviour of reinforced concrete (RC) beams with prestressing and external reinforcement. The M/Ө approach is formed on the fundamental Euler-Bernoulli postulation that plane sections remain plane, but not necessarily on the Euler-Bernoulli corollary of a linear strain profile. Further adaption of the well-established mechanics of partial-interaction (PI) theory introduces a fundamental baseline concept in which residual strains due to time-effects, thermal gradients and prestressing are accounted for in simulating the formation and gradual widening of cracks and the associated effects of tension-stiffening allowing for bond-slip. The effects of concrete softening are incorporated into the M/Ө approach through a size dependent concrete stress-strain relationship based on the mechanics of shear-friction theory which simulates the behaviour of a member once a concrete softening wedge forms. The approach is shown to be able to quantify segmental equivalent flexural rigidities for both instantaneous and time-dependent behaviour, thus removing the reliance on empiricism in quantifying the effects of concrete cracking and softening. In defining the segmental equivalent flexural rigidities of RC beams with both post-tensioned and pre-tensioned reinforcement it is shown how the approach is used to quantify the load-deflection behaviour of the entire member through the application of conventional analysis techniques. The established M/Ө approach is then generically applied to RC beams with both prestressed fibre reinforced polymer (FRP) and steel reinforcement in quantifying the beams instantaneous and sustained loading behaviour through being able to accommodate any conventional method of quantifying the time-dependent parameters. Thus the broad application of the M/Ө approach provides a novel method of simulating...

Construir con tapial: piscina en Toro

Antelo Tudela, Enrique; Sánchez Iglesias, Santiago; Crespo González, Cristóbal; Raya de Blas, Antonio
Fonte: Universidade da Coruña Publicador: Universidade da Coruña
Tipo: Artigo de Revista Científica
SPA
Relevância na Pesquisa
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[Resumen] Este artículo transmite la experiencia arquitectónica obtenida en la construcción con tapial de grandes muros de cerramiento para una piscina en Toro (Zamora). Partiendo de los aspectos compositivos y espaciales se llega a los técnicos, describiendo las soluciones utilizadas, tales como el postensado del tapial. Se prosigue con la descripción de las incidencias y se propone una serie de medidas a considerar en nuevas construcciones de características similares.; [Abstract] Th is article tries to convey the architectural experience gained through the construction of the rammed earth walls of the new Municipal Indoor swimming pool in Toro(Zamora – Spain). From compositional and spatial matters to technical questions,the text describes the solutions used in the construction of the pool enclosure, such as the post-tensioned walls. It continues with a description of the problems found to finally, proposes a number of actions to consider in similar constructions.

Sistema de losas postensadas para fundaciones en arcillas expansivas

Saltarini Korpos, Andrés Alejandro
Fonte: Universidad Andrés Bello Publicador: Universidad Andrés Bello
Tipo: Tesis
ES
Relevância na Pesquisa
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Tesis (Ingeniero Constructor); RESUMEN: Los sistemas de Losas Postensadas en arcillas expansivas, han tenido una amplia difusión en Estados Unidos, como consecuencia de la búsqueda de alternativas de fundación sobre este tipo de suelos. Esta investigación tiene como objetivo principal, exponer el sistema de losas postensadas, como solución de fundación para arcillas expansivas, y su aplicación en nuestro país, además de plantear y analizar las variables que fundamentan la problemática de este tipo de suelos en las fundaciones. Finalmente realizar un análisis técnico económico del sistema y compararlo con soluciones tradicionales. El desarrollo del tema se fundamentó en el conocimiento de la arcilla expansiva, su problemática y los elementos que componen el sistema. Sin embargo, la metodología y conceptos de diseño, se extrajeron de la normativa y experiencia, recopilada de Instituto del postensado de Texas, Estados Unidos. Para esto último fue necesario, investigar las variables relacionas con el clima, de manera de convalidar el sistema a la realidad nacional. Se concluye que el sistema de Losas Postensadas sobre Arcillas Expansivas, tiene grandes ventajas técnicas y económicas, si bien su utilización esta limitada por las variables que fundamentan su diseño...

CFRP Tendons For The Repair Of Post-Tensioned, Ubonded Concrete Buildings

Amato, Lucio Roger
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado Formato: 4511239 bytes; application/pdf
EN; EN
Relevância na Pesquisa
56.85%
The deterioration of prestressed concrete structures due to corrosion is a costly problem. This problem is accelerated in cold weather climates where de-icing salts are used. These salts accelerate the corrosion of the steel tendons greatly reducing the service life of the structures and leading to constant costly repairs. Recent research has shown composite materials such as Fibre Reinforced Polymers (FRP) to be suitable alternatives to steel, providing similar strength without being susceptible to electrochemical corrosion. Carbon FRP in particular has great promise for prestressed applications, showing resistance to corrosion in environments that might be encountered in concrete and experiencing less relaxation than steel. This thesis outlines the testing and implementation of a post-tensioned system that uses CFRP tendons to replace corroded, unbonded post-tensioned steel tendons. This system was then implemented in a parking garage in downtown Toronto. To the author’s knowledge, this is the first example of an unbonded, post-tensioned tendon replacement using FRP tendons. The system used split wedge anchors designed specifically for CFRP tendons at the University of Waterloo. The dead end was anchored by directly bonding the tendon to the concrete slab. Overall...

Post-Fire Assessment of Unbonded Post-Tensioned Concrete Slabs: Strand Deterioration and Prestress Loss

MacLean, Kevin J.N.
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado Formato: 6053766 bytes; application/pdf
EN; EN
Relevância na Pesquisa
66.98%
Unbonded post-tensioned concrete slabs have been widely used in Canada and the United States since the 1960s, as they allow increased span-to-depth ratios and excellent control of deflections compared to non-prestressed reinforced concrete flexural members. The satisfactory fire performance of unbonded post-tensioned concrete slabs in North America was established by a series of standard fire tests performed in the United States during the 1960s. However, there is a paucity of data on the effect of elevated temperatures on cold-drawn prestressing steel, both in terms of post-fire residual mechanical properties and high-temperature stress relaxation, which can lead to significant prestress loss both during and after a fire. A detailed and comprehensive literature review is presented that provides background on the residual mechanical properties of prestressing steel, as well as on the creep-relaxation behaviour experienced at elevated temperatures under stress. The results of two test series are discussed; the first examining the effects of elevated temperatures on the residual mechanical properties of prestressing steel exposed to elevated temperatures. The second test series examines the irrecoverable and significant loss of prestress force that results from steel relaxation and other thermal effects experienced during heating. A preliminary analytical model is presented...

Transient High-Temperature Prestress Relaxation of Unbonded Prestressing Tendons for use in Concrete Slabs

GALES, JOHN
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado Formato: 2014492 bytes; application/pdf
EN; EN
Relevância na Pesquisa
36.18%
Unbonded post-tensioned (UPT) flat plate concrete slabs have seen widespread use in multi-storey office and condominium buildings since the 1960s. The popularity of these systems can be attributed to various economic and structural benefits, including reductions in slab thickness, storey height, building mass, and excellent deflection control over large spans. The “inherent fire resistance” of these systems is often quoted as a key additional benefit as compared with competing structural systems. Such statements are apparently based largely on satisfactory results from large scale standard fire resistance tests performed on UPT slabs during the 1960s and on experience from real fires in UPT buildings. However, much remains unknown about the true structural behaviour of continuous multiple bay UPT slabs in real building fires. For instance, relatively little data exist on the effects of elevated temperature on cold drawn prestressing steel under realistic, sustained service stress levels. The primary objective of this thesis is to provide a greater understanding of the high-temperature performance (predominantly related to prestress relaxation) of prestressing steel used in UPT flat plate slabs. A computational model is developed...

Nonlinear, unbonded, post-tensioned tendon element for concrete structures

Lin, Yuh-Yi, 1957-
Fonte: Universidade da Flórida Publicador: Universidade da Flórida
Tipo: Artigo de Revista Científica Formato: x, 180 leaves : ill. ; 29 cm.
Publicado em //1990 ENGLISH
Relevância na Pesquisa
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(Thesis) Thesis (Ph. D.)--University of Florida, 1990.; (Bibliography) Includes bibliographical references (leaves 177-179).; Typescript.; Vita.; (Statement of Responsibility) by Yuh-Yi Lin.