The goal of the splice girder research project 0-6652 funded by the Texas Department of Transportation is to utilize the full potential of splicing prestressed TX girders continuously. The TX girder family of beams is cost effective alone due to their simple, repetitive fabrication, but to truly optimize their potential would be to span several beams together as one continuous unit. The weight and length restrictions allowed by trucks or barges limit the prestressed beam lengths. Therefore, splicing together prestressed beams becomes the solution to the transporting obstacle. As a result, the prestressed girders will be more competitive to other bridge types such as steel I-girders, steel trapezoidal girders, cable-stayed bridges, and concrete segmental bridges. In fact, a prestressed/post-tensioned concrete bridge is preferred over steel designs in highly corrosive environments such as the coast or in snow regions where de-icing chemicals are used. In comparison, to a segmental box girder bridge, the post-tensioned prestressed bridge has reduced complexity due to fewer segments and the number of reduced joints susceptible to corrosion. The issue that arises with splicing prestressed beams is that in the process of connecting them together an opening must be made to install the post-tensioning (PT) steel strands. The openings are created by installing several steel or plastic circular ducts into the web region. Since the post-tensioning results in a reduction of the concrete web region, a modification is necessary to the shear capacity equation. The experimental study performed at the Ferguson Structural Engineering Laboratory consisted of fabricating and testing two full-scale prestressed Tx46 girders. One girder contained a plastic post-tensioning duct with grout and steel strands installed in the web region. The other beam was a standard Tx46 beam fabricated without a duct. Both beams had a reinforced concrete deck installed with an overhang to model an actual bridge section. Furthermore, the purpose of the standard beam was to serve as a direct comparison to the beam with a duct and determine the actual reduction in shear capacity. The research and findings will include the impact of the plastic duct in the Tx46 compared to the control beam. The failure loads of the test specimens will be compared to the current 2012 AASHTO code predictions for shear design. Also, revisions to the AASHTO code will be recommended if necessary. The primary goal of this research was to improve the design and detailing of the skewed end-blocks commonly used in these beams. As U-beams had been in service for several decades without incident, it was anticipated that there would be little need for change in the design, and the findings of the research would involve a slight tweaking to improve the overall performance. / text

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, extending previous research by others, to predict transient high temperature stress relaxation (i.e., prestress loss) for a tendon in a typical UPT multiple span flat plate concrete slab under transient heating and cooling. The computational model is validated by comparison against a series of novel high temperature experiments on locally-heated, stressed, and restrained prestressing tendons with realistic as-built configurations. Reasonable agreement between measured and predicted prestress losses is observed, although some refinement of the model’s input parameters may be required. Test data also indicate that the most crucial fire scenario on a UPT concrete slab may be localized heating rather than a global, fully developed fire. The model is subsequently used to predict the capacity in flexure and punching shear of a UPT flat plate structure under various spatial and temporal heating regimes. The results highlight the need for particular care in the construction of UPT slabs to ensure adequate, robust concrete cover for structural fire safety. / Thesis (Master, Civil Engineering) -- Queen's University, 2009-09-24 18:27:25.559

[Abstract]Over the last few decades, there has been a rapid increase in the volume and weight of heavy vehicles using national road networks. More than half of the bridges around the world are over forty years old. The deterioration of these existing bridges due to increased traffic loading, progressive structural aging, and reinforcement corrosion from severe environmental conditions has become a major problem in most countries. Several techniques have been used to strengthen these structures around the world. External post-tensioning is one of the widely used strengthening techniques in many countries due to its advantages over other methods. Furthermore, flexural strengthening using external post-tensioning has become a well established technique over the past few decades. However, when external post-tensioning is used to strengthen shear damaged reinforced concrete members, unlike flexural damage, the efficiency is significantly reduced by existing shear cracks.This research study was carried out to investigate the behaviour of reinforced concrete beams with existing shear cracks when strengthened by external means. The study consists of two parts: experimental investigations of reinforced concrete beams with different parameters and numerical analysis of reinforced concrete beams usingsimplified theoretical formulation and finite element modelling.To study the behaviour of shear damaged concrete beams, two different strengthening techniques, namely external post-tensioning and external clamping, were used. In addition to the strengthening, the effect of cracks on the behaviour of reinforced concrete beams was investigated by repairing such cracks using epoxy resin injection. Experimental results showed that existing shear cracks have a substantial effect on the member capacity when strengthened by external posttensioning. Although there are concerns about the practical applications of externalclamping, the experimental results suggest that external clamping could be a more effective technique than external post-tensioning to reduce the effect of existing shear cracks on the behaviour of concrete beams. Furthermore, proper repair of the shear cracks could significantly reduce their impact.In the numerical analysis, a simplified mathematical approach was developed to estimate the capacity of shear damaged reinforced concrete beam by expanding themodified compression field theory (MCFT). In addition to the simplified theoretical formulation, a finite element model was developed using the commercial finite element package, Abaqus. Comparison between the predicted behaviour using finite element analysis (FEA) and the experimental data illustrated that the developed finite element model could be used as a reliable tool to estimate the capacity of shear damaged reinforced concrete beams. A parametric study was conducted to investigate the effect of different parameters such as concrete strength, amount of shear reinforcement and crack width, using the developed finite element model. From the numerical study, it was concluded that the simplified approach developedin this study can be used as a reliable and conservative technique to predict the member capacity of a cracked reinforced concrete beam strengthened by external means. Furthermore, the parametric study showed that crack width is the most sensitive parameter that affects the capacity of a cracked beam strengthened by external post-tensioning.Based on this research study it can be concluded that existing shear cracks have a substantial effect on the behaviour of reinforced concrete beams strengthened byexternal post-tensioning. The simplified mathematical approach developed in this study can be used to estimate the capacity of such beams.

This thesis investigates a parametric study of a flat plate floor system designed using post-tensioning. The load balanced by the post-tensioning, the slab depth, and the strength of concrete were varied to create the parametric study of a hotel/condominium grid layout. In order to perform the parametric study, research was conducted on the development of post-tensioning, methods of analysis for two-way slab design, and post-tensioning methods of analysis. Design was conducted by hand through a series of Excel spreadsheets and compared to results found using the computer analysis program, ADAPT-PT. The designs found in the parametric study were then used to perform a cost analysis across ten cities in the United States: Atlanta, Boston, Chicago, Denver, Houston, Los Angeles, Miami, Phoenix, San Francisco, and Seattle. The designs from the hand analysis and the ADAPT-PT model provided similar results for the post-tensioning, and both methods provide an adequate design. The use of ADAPT-PT is recommended because of its ease of use and quick calculation capabilities. The designs of the hand analysis were quantified and along with unit prices gathered from contractors and suppliers the cost analysis found that the design with 100% of the dead load balanced provided the least expensive solution for all the cities, and the design using a 6000 psi strength concrete provide the most expensive solution for all cities. The least expensive slab design was $9.02 per square foot in Atlanta, Georgia, and the most expensive slab design was $24.96 per square foot in Miami, Florida. A more rigorous parametric study in the future may provide a better optimization for the hotel/condominium slab investigated as the parametric study of this thesis found costs which varied by less than 10% between the most expensive and least expensive slabs in the ten cities.

O presente trabalho faz um estudo da representação da protensão em estruturas de barras através de um Conjunto de Cargas Concentradas Equivalentes para determinação dos esforços solicitantes e dos deslocamentos, gerados pela protensão. O trabalho aborda a conceituação de protensão, forças de desvio e perdas imediatas de protensão. Na sequência discute-se alguns métodos para determinação de esforços de protensão, inclusive para o caso de peças hiperestáticas, como por exemplo o método dos esforços solicitantes iniciais e o da carga distribuída equivalente. A seguir discute-se o algoritmo em estudo - Conjunto de Cargas Concentradas Equivalentes, CCCE (também conhecido como Método da Força Variável), suas vantagens e aplicações. Na parte final compara-se, através de exemplos, a aplicabilidade e precisão do CCCE com alguns dos métodos mais tradicionais citados anteriormente assim como as vantagens e desvantagens de cada um deles. / This work is a study about the representation of the prestressing through a CELG (Concentrated Equivalent Loads Group) in order to determine the internal forces and displacements in prestressed structures, due to prestressing. This study considers the concept of prestressing, deviation forces and immediate loss of prestressing. Furthermore some alternative methods to determine forces of prestressing are discussed including the case of hiperestatic structures e.g. initial forces and equivalent distributed loads. Next, the studied algorithm is discussed - CELG, (also known as Variable Force Method), its advantages and uses. Finally the use and precision of CELG is compared to some of the most traditional methods quoted beforehand and also its advantages and disadvantages.

Engineered wood products (EWP) are becoming extremely popular and a viable material option for the construction of residential, commercial, and hybrid buildings. Cross-laminated timber (CLT) is among one of the many EWP available in North America, which can be utilized for many different applications such as: walls, floors, and roofs. Despite the available requirements in the Canadian blast design standard (CSA, 2012) with regard to the design of wood structures, there are currently no provisions on how to retrofit timber structures to improve their performance when subjected to blast loads. The current study is aimed at investigating the effect of different retrofitting alternatives in order to improve the overall behaviour of CLT when exposed to out-of-plane bending. The experimental program examined the behaviour of seventeen reinforced CLT slabs. Testing was conducted at the University of Ottawa by means of a shock tube capable of simulating high strain rates similar to those experienced during a blast event. The current study was divided into two phases. The first consisted of CLT slabs retrofitted with steel straps where strap spacing, location, and order of installation was investigated. The second phase focused on the development of dynamic properties of CLT panels when reinforced with GFRP. Lay-up configuration and fabric orientation were among the parameters explored. The results from the experimental program show that reinforcing the panels with steel straps had minimal effect on the ultimate strength, but significant levels of post peak resistance and ductility was achieved. The horizontal straps were able to restrict the failure to small regions and to promote flexural failure by preventing rolling shear failure. It also eliminated flying debris and enhanced the ultimate strength, stiffness as well as ductility. Applying GFRP layers enhanced the overall behaviour of the slab resulting in a significant increase in peak resistance, ductility, and stiffness when compared to the dynamic results of an unretrofitted panel. The post peak resistance was also greatly improved. In particular, applying stacked quadraxial lay-up configuration significantly improved the ductility and resulted in the greatest post peak resistance. The effect of steel straps on damaged and retrofitted was relatively minimal, and only partial recovery of the resistance and the stiffness was achieved. GFRP with full confinement yielded better performance compared to the unretrofitted and undamaged counterpart. More work is needed to quantify the benefits of using GFRP in these applications.

Made available in DSpace on 2016-06-02T20:09:11Z (GMT). No. of bitstreams: 1 2580.pdf: 4760065 bytes, checksum: 5236258da515ebb08b8d6b0431607f59 (MD5) Previous issue date: 2009-07-30 / This work shows a calculation sequence to determine and detail the longitudinal and transverse reinforcement of prestesses beams with pre-composed section. All procedures are done in a way that meets all the requirements of NBR6118: 2003 and 9062:2006 Code. It shows how the checks can be made of the ultimate state limit and the cracking service state and determining whether there is need for the isolation of the strand. The prestesses loss are considered taking into account the age of the constituents of the concrete section at the time when each step is performed and the procedure for progressive loss. The assumptions adopted for the calculation as composite section and the respective transverse reinforcement are detailing. It can be done as the detailing of transverse reinforcement with special care for the end of the piece where it is common the use of dapped-end. Four numerical examples are solved showing how the recommended calculation sequence allows the designer immediately realize the best solution, including the need for the use of prestressed strand along the top edge. The results obtained in the examples it can be seen: the advantage of using the section Ibeam, the semi-rigid connection has a limited efficiency even with large amounts of negative reinforcement, because the existence of the dapped-end, that considering the effect of prestressing causes the shear reinforcement required is minimal. Finally we can conclude that in several instances the situation critical for obtaining the longitudinal reinforcement was in service with the decompression. / Este trabalho mostra um roteiro para determinar e detalhar as armaduras longitudinal e transversal de vigas pré-tracionadas com seção composta. Todos os procedimentos são feitos de maneira que atenda a todas as prescrições das normas NBR 6118:2003 e NBR 9062:2006. Apresentam-se como podem ser feitas as verificações do estado limite último assim como em serviço de fissuração e determinando se há necessidade do isolamento das cordoalhas. As perdas de protensão são consideradas levando-se em conta a idade dos concretos constituintes da seção na época em que cada etapa é executada e o procedimento de perdas progressivas. As hipóteses adotadas para o cálculo como seção composta e respectiva armadura de costura são detalhadas. Mostra-se como pode ser feito o detalhamento da armadura transversal com especial cuidado para a extremidade da peça onde é comum o uso de dente Gerber. Quatro exemplos numéricos são resolvidos mostrando como o roteiro recomendado permite ao projetista perceber logo a melhor solução, inclusive da necessidade do uso de protensão junto a borda superior. Pelos resultados obtidos nos exemplos percebe-se: a vantagem do uso da seção em forma de I; que a ligação semi-rígida tem pequena eficiência mesmo com grande quantidade de armadura negativa, devido a existência do dente Gerber; que considerando o efeito da protensão faz com que a armadura de cisalhamento necessária seja a mínima. Finalmente pode-se concluir que nos diversos exemplos a situação determinante para a obtenção da armadura longitudinal foi a em serviço com a descompressão.

O presente trabalho faz um estudo da representação da protensão em estruturas de barras através de um Conjunto de Cargas Concentradas Equivalentes para determinação dos esforços solicitantes e dos deslocamentos, gerados pela protensão. O trabalho aborda a conceituação de protensão, forças de desvio e perdas imediatas de protensão. Na sequência discute-se alguns métodos para determinação de esforços de protensão, inclusive para o caso de peças hiperestáticas, como por exemplo o método dos esforços solicitantes iniciais e o da carga distribuída equivalente. A seguir discute-se o algoritmo em estudo - Conjunto de Cargas Concentradas Equivalentes, CCCE (também conhecido como Método da Força Variável), suas vantagens e aplicações. Na parte final compara-se, através de exemplos, a aplicabilidade e precisão do CCCE com alguns dos métodos mais tradicionais citados anteriormente assim como as vantagens e desvantagens de cada um deles. / This work is a study about the representation of the prestressing through a CELG (Concentrated Equivalent Loads Group) in order to determine the internal forces and displacements in prestressed structures, due to prestressing. This study considers the concept of prestressing, deviation forces and immediate loss of prestressing. Furthermore some alternative methods to determine forces of prestressing are discussed including the case of hiperestatic structures e.g. initial forces and equivalent distributed loads. Next, the studied algorithm is discussed - CELG, (also known as Variable Force Method), its advantages and uses. Finally the use and precision of CELG is compared to some of the most traditional methods quoted beforehand and also its advantages and disadvantages.

Concrete girder bridges are a commonly used type of bridge which can be reinforced withboth regular and post-tensioned reinforcement. At a certain span length, the use of tensionreinforcement becomes a must because regular reinforcement won’t be enough. To get anidea of where this boundary lies, we studied a bridge in this research which is a half-throughbridge intended for railway traffic with the use of post-tensioned reinforcements. Thisbridge has a span of 22,15 metres and it is compared to bridges at the same span andshorter span using regular reinforcements. The analysis in this thesis is made using the finiteelementsprogram Brigade Standard.Two previously executed projects are used as references. A literature study will be carriedout initially, where Eurocodes, old examination projects and other literature on tensionreinforcement are examined.The acquired result is that the tension-reinforced bridge relates to a bridge with about 3/4span with regards to torque over the middle support. The torque over the support is thelimiting factor which causes an exponential increase in the amount of reinforcement atlonger spans. At about 20 metres the amount of necessary reinforcement starts to increaseexponentially and above this span post-tensioning is the preferred method.Torsion at the end support is also a crucial parameter since a regular-reinforced bridge with20-metre span cannot be reinforced to handle this with the current geometry. At a 20-metrespan, actions are therefore required to improve the torsion capacity, for example, increasingthe girder width. This increased girder width could be considered a saving in materials dueto the avoided increment of concrete in the case of tension-reinforced design, where thisincreased width is unnecessary.The total amount of reinforcement, independent of the reinforcement type, is greater in themiddle support of the regular reinforced bridge than the tension reinforced with the samespan. However, the total amount of reinforcement over the entire bridge is higher in thetension reinforced alternative.The result also shows that the tension reinforcement increases the compression force in thebridge and eliminates tension cracks which were expected according to our literature study.

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