Time-Dependent Deformation of Non-Composite and Composite Sand-Lightweight Prestressed Concrete Structures, Phase 1, HR-137, 1969

Presented in this report is an investigation of the use of "sand-lightweight" concrete in prestressed concrete structures. The sand-lightweight concrete consists of 100% sand substitution for fines, along with Idealite coarse and medium lightweight aggregate and Type I Portland Cement.

Creep and Shrinkage Properties of Lightweight Concrete Used in the State of Iowa, HR-136, Phase I, 1968

In February of 1968 a cooperative research project by the Iowa State Highway Commission (Project No. HR-136) and the University of Iowa, Iowa City, Iowa was initiated in order to determine experimentally the creep and shrinkage characteristics of lightweight-aggregate concrete used in the State of Iowa. This report is concerned with Phase 1 of the Project as described in the Prospectus for the project submitted in November of 1967: "The State Highway Commission is planning to conduct pilot studies in prestressed-lightweight structures fabricated with materials that are proposed for use in bridge structures in the near future. Thus, Phase will have as its immediate objective, investigating the materials to be used in the above mentioned pilot studies.” (1) The work described in this report was also carried out in conjunction with a second cooperative project: "Time-Dependent Camber and Deflection of Non-Composite and Composite Lightweight-Prestressed Concrete Beams" (Project No. HR-137).

Preliminary design of a prestressed concrete viaduct

O presente Trabalho Final de Mestrado consiste na elaboração de um Estudo Prévio de um viaduto rodoviário, em betão armado pré-esforçado. O viaduto, com tabuleiro em laje vigada, é constituído por 10 tramos, prevendo-se que seja construído tramo a tramo, com juntas de betonagem a quintos de vão. A plataforma do viaduto é constituída por duas vias de tráfego com 3.5m cada, duas bermas de 1.00 m e dois passeios laterais com 1.10 m cada, perfazendo uma largura total de 11.20. O viaduto localiza-se em Polónia e foi dimensionado de acordo com os Eurocódigos e os Anexos Nacionais desse país.

Estudio de la fisuración en particiones verticales de yeso laminado, producidas por la deformación de forjados

Las exigencias de calidad, tanto en el ámbito de la rehabilitación como en el de las obras de nueva planta, obligan a evitar la fisuración de la tabiquería. Una de sus principales causas es la deformación excesiva de los forjados. Aunque en la mayoría de los casos no tiene efectos estructurales sino solamente estéticos, es necesario tomar precauciones para evitar la fisuración, pues es una de las patologías más frecuentes y en muchos casos motivo de reclamación de los usuarios. El aumento del consumo de los paneles de placa de yeso laminado y lana de roca para la realización de tabiquerías, justifica la necesidad de ahondar en el conocimiento del comportamiento y del mecanismo de fisuración de este material, pues hasta la fecha no se ha encontrado ningún trabajo especificamente dedicado al estudio del comportamiento en fractura de paneles sandwich de placa de yeso laminado y lana de roca en su plano. A la hora de abordar el estudio del comportamiento en fractura del material objeto de esta tesis, es preciso tener en cuenta que se trata de un material compuesto y, como tal, sus propiedades mecánicas y resistentes dependen en gran medida de las de sus componentes. Por tanto, para poder explicar el comportamiento en fractura del panel sandwich, habrá que estudiar también el de sus componentes. Por otro lado, se considera también muy útil disponer de una herramienta de calculo para la simulación de la fractura de paneles sandwich que sea predictiva. Este modelo hará posible facilitar el diseño de tabiquerías que no se fisure con este material, al poder relacionar las flechas que pueden tomar los forjados con su potencial fisuración. Para contrastar y validar un modelo de este tipo, es necesario disponer de suficientes datos experimentales del comportamiento en fractura del panel sandwich de placa de yeso laminado y lana de roca, que se puedan simular numericamente con el mismo. A partir de lo anteriormente expuesto se plantea, en primer lugar, una campaña experimental con el fin de obtener los parámetros necesarios para caracterizar el comportamiento en fractura de los paneles sandwich y sus componentes: placa de yeso laminado y lana de roca, estudiando también, su comportamiento en fractura en Modo Mixto, y el efecto del tamaño en los parámetros del panel. Por otro lado se propone un modelo de cálculo para la simulación de la fractura en Modo Mixto de paneles sandwich de placa de yeso laminado y lana de roca, comprobando la validez del modelo numérico a partir de los resultados experimentales obtenidos en la campaña de ensayos. Finalmente, se aplica el modelo para estudiar la fisuración de tabiquería realizada con el panel sandwich producida por la deformación de forjados unidireccionales realizados con viguetas de hormigón y bovedilla cerámica, por ser esta tipología la más usual en obras de edificación de viviendas. The quality requirements in terms of rehabilitation and new Works, force to prevent cracking on partitions and one of the main causes is the excessive deformation of the floor. In most of the cases, there are any structural damages, only aesthetic effects, but it is necessary to take precautions to avoid cracking because it is one of the most common diseases and in addition is the main reason of user’s complaints. The increased consumption of plasterboard panels and mineral wool used to build partitions, justifies the need to develop a deeper understanding of the cracking behaviour and mechanism, because by now, any specifically work dedicated to the study of fractures behaviour of sandwich plasterboard panels and rock wool has been found. When approaching the study of the fracture behaviour of the material it must bear in mind that we are referring to a composite material and as such, its mechanical and strength properties depend heavily on its components. Therefore, to explain the fracture behaviour of sandwich panels its components must be studied as well. On the other hand, it is also considered very useful to have a calculation tool to simulate the more likely fractures of the sandwich panel in order to predict it. This model used to perform simulations will enable the design of partitions built with these materials without cracks because it will relate the deflections in decks with its potential cracking. To contrast and validate this type of model, it is necessary and imperative to have enough experimental data of the sandwich plasterboard and rock wool fractures in order to enable its numerical simulation with it. On the basis of the above, the question arises firstly an experimental campaign in order to obtain the necessary parameters to characterize the cracking behaviour of sandwich panels and its components: plasterboard and rock wool, studying also its cracking behaviour in a mixed mode fracture and the effect of size parameters of the panel. Furthermore, a calculation model to simulate fractures in mixed mode of the sandwich panels made of plasterboard and rock wool is proposed in order to check the validity of the numerical model, based on experimental results obtained from the test campaign. Finally, this model is applied to study cracking on partitions built with sandwich panels resulting from the unidirectional floor’s deformations built with prestressed concrete beams and slab pottery pieces being this typology the most common one on residential buildings works.

End connections of pretensioned I-beam bridges.

Mode of access: Internet.

Markov chain modeling of evolution of strains in reinforced concrete flexural beams

From the analysis of experimentally observed variations in surface strains with loading in reinforced concrete beams, it is noted that there is a need to consider the evolution of strains (with loading) as a stochastic process. Use of Markov Chains for modeling stochastic evolution of strains with loading in reinforced concrete flexural beams is studied in this paper. A simple, yet practically useful, bi-level homogeneous Gaussian Markov Chain (BLHGMC) model is proposed for determining the state of strain in reinforced concrete beams. The BLHGMC model will be useful for predicting behavior/response of reinforced concrete beams leading to more rational design.

Fracture energy of the concrete-FRP interface in strengthened beams

To determine the load at which FRPs debond from concrete beams using global-energy-balance-based fracture mechanics concepts, the single most important parameter is the fracture energy of the concrete-FRP interface, which is easy to define but difficult to determine. Debonding propagates in the narrow zone of concrete, between the FRP and the (tension) steel reinforcement bars in the beam, and the presence of nearby steel bars prevents the fracture process zone, which in concrete is normally extensive, from developing fully. The paper presents a detailed discussion of the mechanism of the FRP debonding, and shows that the initiation of debonding can be regarded as a Mode I (tensile) fracture in concrete, despite being loaded primarily in shear. It is shown that the incorporation of this fracture energy in the debonding model developed by the authors, details of which are presented elsewhere, gives predictions that match the test results reported in the literature. © 2013 Elsevier Ltd.

Monitoring and repair of an impact damaged prestressed bridge

This paper details the monitoring and repair of an impact damaged prestressed concrete bridge. The repair was required following an impact from a low-loader carrying an excavator while passing underneath the bridge. The repair was carried out by preloading the bridge in the vicinity of the damage to relieve some prestressing. This preload was removed following the hardening and considerable strength gain of the repair material. The true behaviour of damaged prestressed concrete bridges during repair is difficult to estimate theoretically due to lack of benchmarking and inadequacy of assumed damage models. A network of strain gauges at locations of interest was thus installed during the entire period of repair. Effects of various activities were qualitatively and quantitatively observed. The interaction and rapid, model-free calibration of damaged and undamaged beams, including identification of damaged gauges were also probed. This full scale experiment is expected to be of interest and benefit to the practising engineer and the researcher alike.

Shear behaviour of steel-fibre-reinforced concrete simply supported beams

The structural behaviour of steel-fibre-reinforced concrete beams was studied using non-linear finite-element analysis and existing experimental data. The work aim was to examine the potential of using steel fibres to reduce the amount of conventional transverse steel reinforcement without compromising ductility and strength requirements set out in design codes. To achieve this, the spacing between shear links was increased while steel fibres were added as a substitute. Parametric studies were subsequently carried out and comparisons were also made with BS EN 1992-1-1 predictions. It was concluded that the addition of steel fibres enhanced the load-carrying capacity and also altered the failure mode from a brittle shear mode to a flexural ductile one. The provision of fibres also improved ductility. However, interestingly it was found that adding excessive amounts of fibres led to a less-ductile response. Overall, the study confirmed the potential for fibres to compensate for a reduction in conventional shear reinforcement.

Interface slip control for CFRP-concrete composite beams

Carbon fibre reinforced polymer (CFRP) has been used frequently to retrofit concrete structures. Strengthening efficiency is related to the CFRP application process and the characteristics of the bonding agent. In this paper the mechanism of interface shear behaviour in CFRP to concrete beams is discussed considering previous test observations and mathematical models. This paper then discusses the consequences of introducing interface slip which reduces the integrity of the composite section, however improve ductility and delay debonding failure. The paper suggests that using softer bonding agent as well as setting limits on the interface slip could ensure acceptable serviceability and ductile behaviour.

Shear strength of reinforced concrete circular cross-section beams

A proposed adequation of NBR 6118, Item 7.4, related to shear strength of reinforced concrete beams is presented with aims to application on circular cross-section. The actual expressions are most suitable to rectangular cross-section and some misleading occurs when applied to circular sections at determination of VRd2, Vc and Vsw, as consequence of bw (beam width) and d (effective depth) definitions as well as the real effectiveness of circular stirrups. The proposed adequation is based on extensive bibliographic review and practical experience with a great number of infrastructure elements, such as anchored retaining pile walls, where the use of circular reinforced concrete members is frequent.

Investigation of prestressed reinforced concrete for highway bridges.

Mode of access: Internet.

Greener and leaner : unleashing capacity of railroad concrete ties via limit states concept

New knowledge has raised a concern about the cost-ineffective design methods and the true performance of railroad prestressed concrete ties. Because of previous knowledge deficiencies, railway civil and track engineers have been aware of the conservative design methods for structural components in any railway track that rely on allowable stresses and material strength reductions. In particular, railway sleeper (or railroad tie) is an important component of railway tracks and is commonly made of prestressed concrete. The existing code for designing such components makes use of the permissible stress design concept, whereas the fiber stresses over cross sections at initial and final stages are limited by some empirical values. It is believed that the concrete ties complying with the permissible stress concept possess unduly untapped fracture toughness, based on a number of proven experiments and field data. Collaborative research run by the Australian Cooperative Research Centre for Railway Engineering and Technologies (Rail CRC) was initiated to ascertain the reserved capacity of Australian railway prestressed concrete ties that were designed using the existing design code. The findings have led to the development of a new limit-states design concept. This paper highlights the conventional and the new limit-states design philosophies and their implication to both the railway community and the public. © 2011 American Society of Civil Engineers.

Briefing: Limit states design of railway concrete sleepers

Recently updated information has raised a concern over not only the existing cost-ineffective design method but also the unrealistic analysis mode of railroad prestressed concrete sleepers. Because of the deficient knowledge in the past, railway civil engineers have been mostly aware of the over-conservative design methods for structural components in any railway track, which rely on allowable stresses and material strength reductions. Based on a number of proven experiments and field data, it is believed that the concrete sleepers which complied with the allowable stress concept possess unduly untapped fracture toughness. A collaborative research project run by the Australian Cooperative Research Centre for Railway Engineering and Technologies (RailCRC) was initiated to ascertain the reserved capacity of Australian railway prestressed concrete sleepers designed using the existing design code. The findings have led to the development of a new limit states design concept. This briefing highlights the conventional and the new limit states design philosophies and their implication to both the railway and the public community.