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The first objective of this thesis was to determine the material properties of grade 270 and grade 300 prestressing strand of various sizes. Tension tests were performed on each type of strand. The data from these tests was used to determine modulus of elasticity, yield stress, ultimate stress, and ultimate elongation for each strand. The yield stresses and ultimate stresses for many of the strands did not meet the requirements found in ASTM A416. The ultimate elongation results far exceeded the requirements and the measured elastic moduli were near the modulus recommended by AASHTO LRFD. A secondary objective from the tension tests was to evaluate a gripping method which used aluminum tubing to cushion the strands against notching. The grips performed very well. Most of the strand breaks did not occur in the grips and when a strand did break in the grips, the failure occurred after significant post-yield elongation. The second objective was to evaluate the bond properties of grade 270 and grade 300 prestressing strands. The North American Strand Producers (NASP) Bond Test and Large Block Pullout Test (LBPT) were performed on six different strand grade and strand size combinations. Both of the tests are simple pullout tests on untensioned strand. The results for each strand type were compared to one another as well as to measured transfer and development lengths from beams using the strand from the same reel. All of the strands showed sufficient bond in the beams, but one strand type did fail both the NASP Test and the LBPT. Both pullout tests were acceptable methods to evaluate strand surface condition and the benchmarks set for 0.5 in. diameter regular strand were conservative for the strands used in this thesis. Little difference was evident in the bond performance of grade 270 and grade 300 prestressing strand. / Master of Science

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.

The introduction of fibre-reinforced polymers (FRPs) to the field of civil engineering has led to numerous research efforts focusing on a wide range of applications where properties such as high strength, light weight or corrosion resistance are desirable. In particular, FRP materials have been especially attractive for use as internal reinforcement in reinforced concrete (RC) structures exposed to aggressive environments due to the rapidly deteriorating infrastructure resulting from corrosion of conventional steel reinforcement. While FRPs have been successfully implemented in a variety of structural applications, little research has been conducted on the use of FRP reinforcement for short span slab bridges. Furthermore, the behaviour of FRP-RC flexural members cast with self-consolidating concrete (SCC) is largely absent from the literature. The present study investigates the behaviour of an all-FRP reinforcement system for slab bridges which combines lower cost glass FRP (GFRP) reinforcing bars with high performance carbon FRP (CFRP) prestressed tendons in SCC to produce a structure which is both cost-efficient and characterized by excellent structural performance at the serviceability, ultimate and fatigue limit states. An extensive experimental program comprised of 57 large or full-scale slab strips was conducted to investigate the effects of reinforcement type, reinforcement ratio, prestressing level and shear reinforcement type on the flexural performance of slab bridges under both monotonic and fatigue loading. The proposed reinforcement system was found to display excellent serviceability characteristics and high load capacities as well as significant deformability to allow for sufficient warning prior to failure. Lastly, the use of post-tensioned CFRP tendons limited the stresses in the GFRP reinforcing bars leading to significantly longer fatigue lives and higher fatigue strengths compared to non-prestressed slabs. Analytical models were used to predict the behaviour of the slab bridge strips at service and at ultimate. Where these models failed to accurately represent the experimental findings, simple modifications were proposed. The results from ancillary tests were also used to modify existing analytical models to predict the effects of fatigue loading on the deflection, crack width, shear resistance and flexural capacity of each of the tested slabs.

Bei dem Prozess einer Wasserstoffinduzierten Spannungsrisskorrosion (H-SpRK) handelt es sich um einen zeitabhängigen Vorgang, der zu einer Reduzierung der Duktilität und Widerstandskraft des Spannstahls führt und daraus resultierend ein sprödes und schlagartiges Versagen eines Spannbetonbauwerkes zur Folge haben kann. Der Prozess selbst und insbesondere auch die ihn beeinflussenden Parameter sind für die im Bauwesen verwendeten hochfesten Spannstähle älterer Produktion weitestgehend unerforscht. Die Relevanz für bestehende Bauwerke ist jedoch nicht zuletzt durch einzelne dokumentierte und untersuchte Schadensfälle nachgewiesen. Ziel der vorliegenden Arbeit war es, die zur Verfügung stehenden Bauwerksuntersuchungen aus den zurückliegenden ca. 10 Jahren statistisch zu analysieren und auszuwerten. Auf dieser Basis war ein Berechnungsmodell wahrscheinlichkeitstheoretischer Basis zu entwickeln, mit dem die Gefahr eines spröden Bauwerksversagens für das Gesamttragwerk beurteilt und hinsichtlich der Auswirkungen auf das einzuhaltende Sicherheitsniveau bewertet werden kann. Es wurden insgesamt 31 Bauwerksuntersuchungen statistisch ausgewertet und beurteilt. Die zur Verfügung stehenden Daten wurden analysiert und hinsichtlich der Prüfqualität sowie der Quantität der Proben bewertet. Dabei war festzustellen, dass aufgrund fehlender konkreter Vorgaben im Regelwerk eine sehr heterogene Datenbasis vorliegt. Nicht alle Untersuchungsergebnisse konnten in die weitere Auswertung einbezogen werden. Die in ausreichender Datenqualität und Datenumfang geeigneten Untersuchungen wurden hinsichtlich ihrer Relevanz für den Prozess einer H-SpRK analysiert und die Auswirkungen einzelner Parameter bewertet. Im Ergebnis der materialtechnischen Untersuchungen und statistischen Auswertung der Bauwerksuntersuchungen wurde ein Berechnungsmodell vorgestellt, das den gleichzeitigen Ausfall von Spannstahl in allen Bereichen des Bauwerkes berücksichtigt. Zusätzlich zum Standardverfahren des beschriebenen Vorgehens wird das Modell um den Ansatz eines korrelierten Spannstahlausfalls erweitert. Außerdem wird für Bauwerke mit einem statisch unbestimmten Anteil der Vorspannung sowie für Konstruktionen mit gestaffelter Spannstahlbewehrung die Anwendung des Verfahrens konkretisiert. Neben der Erstellung des Berechnungsmodells wurden Vorschläge zu Vorgaben für die Bauwerksprüfung vorgestellt. Dazu zählen insbesondere die Festlegung von Prüfintervallen sowie einheitliche Vorgaben zu den verwendeten Prüfmethoden und -verfahren. Bezüglich der Festlegung von Mindestumfängen von Proben wird zwischen bestehenden und auch weiter zu nutzenden Bauwerken einerseits sowie Probennahmen im Rahmen von Rückbaumaßnahmen unterschieden.

The manufacturing process ‘long line method’ has shown many advantages when producing prestressed concrete sleepers, such as rapid production and low cost. However, there have been certain difficulties when cutting the 100 m long concrete blocks into sleepers. The sleepers tend to crack when the diamond cutting blade cuts through the last strands. Moreover, the shape and size of the cracks varies from one sleeper to another. Although these cracks may not affect the load carrying capacity, they will not be aesthetically pleasing. No earlier studies within the area have been found, i.e. diamond cutting of prestressed concrete blocks. As a result, there have been certain difficulties when approaching the problem. Finite element analysis has been proven to be a useful tool when analyzing stress variation. Throughout this project, the cutting simulation has been analyzed using the finite element analysis software ABAQUS. To summarize, stress variation has been examined during different cutting depths. The results from the FE model shows that no critical values were reached in the areas expected to have cracks. The true cause of the problem could not be specified. Therefore, further studies are needed yet this thesis could be a good foundation.

The introduction of fibre-reinforced polymers (FRPs) to the field of civil engineering has led to numerous research efforts focusing on a wide range of applications where properties such as high strength, light weight or corrosion resistance are desirable. In particular, FRP materials have been especially attractive for use as internal reinforcement in reinforced concrete (RC) structures exposed to aggressive environments due to the rapidly deteriorating infrastructure resulting from corrosion of conventional steel reinforcement. While FRPs have been successfully implemented in a variety of structural applications, little research has been conducted on the use of FRP reinforcement for short span slab bridges. Furthermore, the behaviour of FRP-RC flexural members cast with self-consolidating concrete (SCC) is largely absent from the literature. The present study investigates the behaviour of an all-FRP reinforcement system for slab bridges which combines lower cost glass FRP (GFRP) reinforcing bars with high performance carbon FRP (CFRP) prestressed tendons in SCC to produce a structure which is both cost-efficient and characterized by excellent structural performance at the serviceability, ultimate and fatigue limit states. An extensive experimental program comprised of 57 large or full-scale slab strips was conducted to investigate the effects of reinforcement type, reinforcement ratio, prestressing level and shear reinforcement type on the flexural performance of slab bridges under both monotonic and fatigue loading. The proposed reinforcement system was found to display excellent serviceability characteristics and high load capacities as well as significant deformability to allow for sufficient warning prior to failure. Lastly, the use of post-tensioned CFRP tendons limited the stresses in the GFRP reinforcing bars leading to significantly longer fatigue lives and higher fatigue strengths compared to non-prestressed slabs. Analytical models were used to predict the behaviour of the slab bridge strips at service and at ultimate. Where these models failed to accurately represent the experimental findings, simple modifications were proposed. The results from ancillary tests were also used to modify existing analytical models to predict the effects of fatigue loading on the deflection, crack width, shear resistance and flexural capacity of each of the tested slabs.

Prestressed hollow core slabs are essential components in structures such as bridges, parking garages, marine structures, and commercial and industrial buildings. Material degradation and altered functional requirements may seriously threaten the structural integrity of these reinforced concrete structures. Using FRP composites, the NSM strengthening technique presents a viable solution to these challenges. However, further investigation is required to establish comprehensive empirical design guidelines. The intent of this research project is to investigate the NSM technique in conjunction with common design concepts such as prestressed concrete, precast hollow core slabs, the complex behaviour of disturbed regions, and fiber-reinforced composite materials. An experimental program was developed, which included eleven full-scale slab specimens, subject to a four-point load configuration. The main parameters included the prestressing reinforcement ratio, CFRP strengthening ratio, and in-service opening location. Experimental results showed that prestressed concrete strengthened in flexure with NSM-CFRP is a viable technique for lower reinforcement ratios.

Historical monuments are the most invaluable reflections of our architectural heritage and cultural identity, both of which have significant roles to create a strong link between the past and the present. They should be conserved in their own settings with their original characteristics or with as minimum changes as possible. However, natural or man-made hazards cause a serious risk for the survival of historical monuments. While some of them require to be strengthened only, some should be relocated to a new site since there are no means to save them without transporting. In this study, an innovative methodology is developed in a general sense for transporting historical masonry monuments without destructing their unity. In the proposed methodology, which is applicable especially to the slender historical structures, it is aimed to transport the structure by tilting it up to a horizontal ground level without dismantling into pieces. Due to the fact that masonry is a very brittle material, externally located prestressed cables are used to strengthen the structure against tension forces, which occur at the time of tilting. Hasankeyf, which is the cradle of various civilizations, is an impressive medieval city located in Mesopotamia region in Turkey. Unfortunately, this unique heritage will be flooded by the reservoir of Ilisu Dam unless the project is cancelled. Therefore, a masonry minaret located in Hasankeyf is selected as a case for this study. Because of the non-homogeneous characteristics of the structural material, Finite Element Method, as a powerful analytical modeling tool, is used in order to evaluate the validity and effectiveness of the proposed methodology. Finally, it is certified that this methodology is successfully applicable for the relocation of historical masonry monuments.