To investigate the benefit induced by adding a small amount of bonded reinforcing steel into a fully unbonded prestressed concrete beam, two well-founded and straightforward approaches for predicting tendon stress are proposed. The primary approach utilizes a flexural analysis to calculate member deformation. The supplementary approach employs a truss model to consider the additional member deformation due to shear force. Both approaches use a simplified iterative method. With these two approaches, a systematic parametric study is conducted to investigate the effects of various factors. The results indicate that adding little bonded reinforcement does significantly increase the stress increment in unbonded tendons at ultimate state for one-point loading as expected. Moreover, a lower span-to-depth ratio, the use of high-strength concrete, and a smaller mechanical reinforcement ratio also raise the stress increment.

To investigate the benefit induced by adding a small amount of bonded reinforcing steel into a fully unbonded prestressed concrete beam, two well-founded and straightforward approaches for predicting tendon stress are proposed. The primary approach utilizes a flexural analysis to calculate member deformation. The supplementary approach employs a truss model to consider the additional member deformation due to shear force. Both approaches use a simplified iterative method. With these two approaches, a systematic parametric study is conducted to investigate the effects of various factors. The results indicate that adding little bonded reinforcement does significantly increase the stress increment in unbonded tendons at ultimate state for one-point loading as expected. Moreover, a lower span-to-depth ratio, the use of high-strength concrete, and a smaller mechanical reinforcement ratio also raise the stress increment.

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, the system was shown to work and provide a durable solution for unbonded post-tensioning systems. The CFRP tendon was successfully inserted in the opening left by the removal of the corroded tendon and stressed. It was found that the current anchorage configuration experienced large load losses of up to 60 % during the transfer. Changing the orientation of the anchor was found to reduce the load lost to a range of 1 % to 9 %. / Thesis (Master, Civil Engineering) -- Queen's University, 2009-04-09 15:30:59.865

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第21364号 / 工博第4523号 / 新制||工||1704(附属図書館) / 京都大学大学院工学研究科建築学専攻 / (主査)教授 西山 峰広, 教授 竹脇 出, 准教授 倉田 真宏 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

<p>If designed and constructed properly, post-tensioned construction can provide improved durability and offers the ability to construct longer span bridges and curved girders. Furthermore, this method of construction has become economically competitive with traditional, pretensioned concrete and steel plate girder bridges. A critical issue, however, has been corrosion of the steel strand. While grouting has been the primary corrosion protection method for the strand, experience has shown that grouting presents its own problems and limitations that compromised the durability and service-life of bridges. As a result, unbonded post-tensioning has gained interest as it eliminates issues with grouting and allows for inspection as well as future strand replacement. The behavior and strength of structures constructed with unbonded post-tensioning, however, is not well understood, especially shear strength. Therefore, the objective of this research investigation is to evaluate the structural performance of prestressed girders containing unbonded tendons with a primary focus on shear strength. The scope of this phase of the research was to develop the means and methods to construct and test girder specimens with multiple design criteria and allow evaluation of multiple test variables. The research developed the materials and procedures to enable the large scale testing program to be developed. Finally, the procedures developed were verified through the construction of the initial set of test specimens and testing of the first shear specimen.</p>

O presente trabalho aborda a utilização da protensão não aderente em edifícios residenciais e comerciais de concreto, focando os aspectos referentes às soluções com protensão aderente e não aderente e em concreto armado, para o consumo de materiais, notadamente: concreto, fôrmas e armaduras. São considerados três diferentes sistemas estruturais, sendo estes: laje plana maciça apoiada sobre pilares; laje plana nervurada apoiada sobre pilares e laje nervurada apoiada em vigas faixa protendidas sobre pilares. São apresentados estudos destes casos com a utilização da ferramenta computacional de análise estrutural TQS, a qual é baseada na análise por grelha. São comparados os índices de consumo de materiais para os dois referidos sistemas de protensão, discutindo os limites de sua utilização. Como resultados, o estudo fornece conclusões satisfatórias para utilização da protensão, tanto aderente quanto não aderente, em relação ao concreto armado. Ainda, o sistema de protensão aderente mostrou-se ligeiramente mais econômico, do ponto de vista de consumo de materiais, porém, é um sistema com produtividade inferior às soluções com protensão não aderente, tornando esta última solução, a mais adotada no cotidiano dos escritórios de cálculo de engenharia civil dentre as citadas / The present work deals the use of the prestressed unbonded tendons in residential and commercial concrete buildings, pointing out aspects to the application with bonded and unbonded prestressing and reinforced concrete, regarding the consumption such as concrete, molds and reinforcing steel. Three different structural systems are considered: flat plate and columns; waffle slab and columns and waffle slab (non prestressed) in prestressed strip beams supported by columns. Case studies are presented with the use of the software of structural analysis TQS, which is based on the grillage analogy method. The consumption of materials is compared for the two referred prestressing systems, discussing the limits of their application. Based on the developed analyses, the study supplies satisfactory conclusions for use of the prestressing systems (bonded and unbonded), compared to reinforced concrete systems. With relation to the consumption of materials, the use of bonded tendons is a bit more cost effective, however, with smaller productivity than tendons with prestressed unbonded tendons, being the last one the more usual prestressing systems. Still, the system of prestressed bonded tendons was shown more economical, of the point of view of materials consumption, however, it is a system with inferior productivity to the solutions with prestressed unbonded tendons adopted in civil engineering offices nowadays

A protensão não-aderente caracteriza-se pela liberdade de deslocamento relativo entre o cabo de protensão e a fibra de concreto adjacente. A tensão na armadura de protensão no estado limite último é de difícil obtenção, não sendo dependente apenas das deformações em uma determinada seção transversal, mas sendo função de todas as deformações que ocorrem no concreto adjacente ao perfil de protensão. Para que seja obtida a tensão última, é necessária a integração das curvaturas ao longo de todo o elemento a fim de se obter o alongamento no cabo de protensão, o que se consegue com precisão apenas recorrendo-se a ferramentas numéricas, devido às não-linearidades físicas envolvidas no problema. O método construtivo com protensão não aderente vem sendo cada vez mais utilizado na execução de edifícios no Brasil. O principal sistema de protensão não aderente é o que utiliza a mono-cordoalha engraxada e plastificada, que alia os benefícios da protensão e a simplicidade necessária às obras moldadas no local. Apesar disso, não há no Brasil um volume de pesquisa sobre o comportamento dos elementos com protensão não aderente, compatível com a demanda da indústria da construção civil. Visando contribuir para o desenvolvimento das formulações nacionais de projeto dos elementos com protensão não aderente, o presente trabalho é a continuação de uma pesquisa que vem sendo realizada no Programa de Pós-Graduação em Engenharia Civil – PPGEC/UFRGS, a qual foi iniciada com a implementação de um modelo numérico capaz de analisar elementos com protensão não aderente e seguida de uma análise paramétrica sobre as principais variáveis que influenciam na tensão última na armadura de protensão. O trabalho que ora se apresenta traçou uma correlação entre os resultados não-aderentes obtidos da análise paramétrica com resultados aderentes, os quais são de mais fácil obtenção, pois se baseiam na compatibilidade de deformações na seção transversal. Foram feitas análises numéricas e analíticas com aderência dos mesmos protótipos estudados anteriormente sem aderência. Os resultados obtidos mostraram incrementos de tensão maiores no caso aderente, bem como maiores capacidades portantes. Estudou-se também uma metodologia capaz de computar a tensão última na armadura não aderente com análises do tipo compatibilidade de deformações, com a utilização de um coeficiente Lo/L redutor de aderência. Os resultados iniciais mostraram-se bons para carregamento nos terços, mas insatisfatórios para carregamentos distribuído e concentrado. Através de um ajuste no coeficiente Lo/L baseando-se nos dados da pesquisa precedente, bons resultados foram obtidos para todos os tipos de carregamento. A metodologia apresentada foi validada pela comparação com diferentes protótipos analisados numericamente, bem como protótipos ensaiados experimentalmente por diversos autores. / Unbonded post-tensioning is characterized for allowing relative displacement between the tendon and the concrete adjacent fiber. The ultimate stress in the unbonded tendon is difficult to be obtained, because it is not only dependent on the deformed shape of a cross section, but on the whole deformations occurring in the tendon profile adjacent concrete. To evaluate this ultimate stress, it is necessary to integrate all curvatures along the whole element, in order to obtain the total tendon elongation. This can only be precisely obtained using numerical tools, due to the non-linear factors involved in the problem. Unbonded post-tensioning is becoming ever more used in Brazilian building construction. The main unbonded post-tensioning system uses the unbonded mono-strand, that joins the benefits of prestressing with the necessary building simplicity. Nevertheless, there is no research effort in Brazil compatible with the construction industry demand. This study seeks to contribute to the development of the national formulations design of unbonded posttensioning elements. This work is a continuation of a research being undertaken at PPGEC/UFRGS. A numerical model able to determine the behavior of unbonded posttensioned elements was first developed, followed by a parametric study about the main parameters influencing the ultimate stress in unbonded tendons. The present work traced a correlation between the results for unbonded elements, obtained from the parametric analysis, with results for bonded elements. The latter are easily obtained, because they are based on the compatibility of strains in the cross section. Numerical and analytical calculations were performed for the same prototypes studied in the previous research, but now considering the existence of bond in the tendons. The results showed greater increments in stress for the bonded cases and also greater ultimate resistance. It was also devised a calculation method able to determine the ultimate stress in the unbonded tendon using an analysis similar to strain compatibility, but with a reduction bond coefficient Lo/L. The initial results obtained for a third-point loading showed a good agreement, but that not happened for the results of distributed and concentrated loads. However, by an adjustment of the Lo/L coefficient, based on the data of the previous research, good agreement was observed for all loading types. The presented methodology was validated by comparing results with other prototypes analyzed by the numerical model, and also results of experimental studies carried out by several authors.

Estruturas com protensão não aderente estão sendo utilizadas como uma alternativa na tecnologia de projeto e execução de edifícios. Este trabalho apresenta a análise numérica de estruturas com protensão não aderente. Para este fim, foi desenvolvido um programa computacional onde implementou-se um modelo não linear físico e geométrico através do método dos elementos finitos. O comportamento dos materiais é descrito por um modelo elasto-viscoplástico. No concreto, são utilizados elementos finitos isoparamétricos tridimensionais. Para representar o seu comportamento após a fissuração é utilizado o modelo de fissuras distribuídas. As armaduras são incluídas através do modelo incorporado, utilizando-se de elementos unidimensionais isoparamétricos.As armaduras passivas são consideradas como uma linha de material mais rígido no interior do elemento de concreto, existindo uma aderência perfeita entre o concreto e o aço. Nas armaduras não aderentes, é considerada a compatibilidade de deslocamentos entre os materiais apenas nas ancoragens, sendo que a armadura pode movimentar-se livremente no interior do concreto. O modelo não linear geométrico, utilizado para o concreto e para a armadura, foi desenvolvido com base na formulação Lagrangeana Total, considerando grandes deslocamentos e pequenas deformações. Para verificar a precisão do modelo computacional, compararam-se resultados numéricos com valores experimentais disponíveis na literatura. / Unbonded prestressed concrete structures have been increasingly used as an alternative in the technology of design and construction of buildings. This work presents a numerical analysis of unbonded prestressed concrete structures. To accomplish this, a computational program has been developed in which a physical and geometrical nonlinear model was implemented through the finite element method. Materials behavior has been described through an elasto-viscoplastic model. In the concrete, a threedimensional isoparametric finite element has been used. To represent its behavior after cracking, the smeared cracking model has been used to. The prestressing tendons and reinforcement have been included according with the embedded model approach by the use of one-dimensional isoparametric elements. The reinforcement has been considered in the model as a line of a stiffer material inside the concrete element, with a perfect bonding between concrete and steel. As for the unbonded tendons, displacement compatibility between materials has been considered only at the anchorages, but they are allowed to move freely along their length inside the concrete. The geometric nonlinear model that has been used for the concrete, reinforcement and tendons has been developed according to the Total Lagrangean formulation, considering large displacements and small strains. In order to evaluate the accuracy of the computational model, numerical results have been compared with experimental values available in the literature.

Minimum impact construction for bridge building is a growing demand in modern urban environments. Pre-cast segmental construction is one solution that offers low-impact, economical, and aesthetically pleasing bridges. The standardization of pre-cast concrete sections and segments has facilitated an improved level of economy in pre-cast construction. Through the development of high performance materials such as high strength fibre-reinforced concrete (FRC), further economy in pre-cast segmental construction may be realized. The design of pre-cast bridges using high-strength FRC and external unbonded tendons for cantilever construction may provide an economical, low-impact alternative to overpass bridge design. This thesis investigates the feasibility and possible savings that can be realized for a single cell box girder bridge with thin concrete sections post-tensioned exclusively with external unbonded tendons in the longitudinal direction. A cantilever-constructed single cell box girder with a curtailed arrangement of external unbonded tendons is examined.

Minimum impact construction for bridge building is a growing demand in modern urban environments. Pre-cast segmental construction is one solution that offers low-impact, economical, and aesthetically pleasing bridges. The standardization of pre-cast concrete sections and segments has facilitated an improved level of economy in pre-cast construction. Through the development of high performance materials such as high strength fibre-reinforced concrete (FRC), further economy in pre-cast segmental construction may be realized. The design of pre-cast bridges using high-strength FRC and external unbonded tendons for cantilever construction may provide an economical, low-impact alternative to overpass bridge design. This thesis investigates the feasibility and possible savings that can be realized for a single cell box girder bridge with thin concrete sections post-tensioned exclusively with external unbonded tendons in the longitudinal direction. A cantilever-constructed single cell box girder with a curtailed arrangement of external unbonded tendons is examined.