This thesis compares the consumption of primary superstructure material in a conventional single span CPCI system with those of double-T alternatives. The CPCI system is currently the preferred bridge type for short and medium spans in Canada, despite its relatively inefficient use of materials due to imperfect live load sharing among multiple parallel girders. The double-T alternatives utilize slender double-T cross-sections, fully precast segments, and post-tensioning in both longitudinal and transverse direction. The economy of the CPCI and double-T systems is compared within the framework of four sample designs. The results indicate that the double-T systems are in general more efficient than the CPCI system and have the potential to achieve better economy.

This thesis compares the consumption of primary superstructure material in a conventional single span CPCI system with those of double-T alternatives. The CPCI system is currently the preferred bridge type for short and medium spans in Canada, despite its relatively inefficient use of materials due to imperfect live load sharing among multiple parallel girders. The double-T alternatives utilize slender double-T cross-sections, fully precast segments, and post-tensioning in both longitudinal and transverse direction. The economy of the CPCI and double-T systems is compared within the framework of four sample designs. The results indicate that the double-T systems are in general more efficient than the CPCI system and have the potential to achieve better economy.

Thesis (Ph. D.)--University of Texas at Austin, 1999. / Vita. Includes bibliographical references (leaves 306-312). Available also in a digital version from Dissertation Abstracts.

Thesis (M.S.)--Florida State University, 2006. / Advisor: Kamal Tawfig and Primus Mtenga, co-advisors, Florida State University, College of Engineering, Dept. of Civil & Environmental Engineering. Title and description from dissertation home page (viewed Sept. 15, 2006). Document formatted into pages; contains ix, 87 pages. Includes bibliographical references.

Due to the unbonded nature of tendons to the slab within Unbonded Post Tensioned (UPT) concrete structures, tendon stress relaxation under heating affects all regions of the slab spanned by the tendon; not just in the locality of the fire. The numerical modelling of bonded and unbonded post tensioned concrete structures in fire has been performed to some degree, notably by Bailey and Ellobody. The consideration of elevated temperature creep to the relaxation of tendon prestress however, has not been considered. This thesis attempts to incorporate a uniaxial creep strain rate function of stress and temperature into the commercial FE software package Abaqus, compatible for use within the in-built multiaxial metal plasticity constitutive framework. What follows is a validation study of the Harmathy’s uniaxial creep strain accumulation function via the modelling of stress relaxation in isolated, tensioned and heated prestressing steel tendons, against experimental data. From here, UPT concrete slab models are analysed whilst exposed to a standard fire temperature-time curve and subsequently allowed to cool. Tendon prestress relaxation and resulting UPT concrete slab deflection is compared, where tendon creep is explicitly modelled, as opposed to implicitly covered by Eurocode 2 determined temperature dependent stress-strain curves. Following this, a large scale continuous one-way spanning UPT concrete structural model is developed to consider global structural behaviour resulting from localised fire, where realistic boundary conditions such as beam rotation and deflection are permitted. The ignorance of explicit elevated temperature creep consideration, in prestressing steel tendons, is commonly justified through the implicit accountability stated within Eurocode 2 temperature dependent stress-strain curves. This however is not completely true; Eurocode 2 states implicit accountability only holds should the tendon be heating at a rate within the bounds of 2⁰C/min to 50⁰C/min. Where only heating of a UPT concrete slab is considered, evidence from this thesis suggests Eurocode 2 determined stress-strain curves can implicitly account for accumulated creep strain up to limited temperatures. Prestressing steel tendons are however embedded within a concrete slab through which thermal gradients build up during fire. This means heat transfer can continue to the tendon, increasing its temperature postfire at an ever decreasing rate until it reaches its peak. Should post-fire cooling behaviour not be considered, continued tendon heating and subsequent creep strain accumulation will be ignored. Further, during the transition from heating to cooling within the tendon, it will be exposed to elevated temperatures with a rate of change below 2⁰C/min, whereby Eurocode 2, as stated cannot implicitly account for creep. It is shown, a significant degree of subsequent relaxation of prestress, UPT concrete slab deflection and concrete damage in hogging can occur during this phase of postfire behaviour, where the tendon temperature peaks during its transition from heating to cooling. In order to justify non consideration of creep, it should be shown tendon temperature will remain suitably low throughout the entire heating-cooling regime to which the UPT concrete slab is exposed. This must be achieved through adequate specification of minimum concrete cover to tendons to limit tendon temperature exposure for a given parametric fire curve duration, including the potential continued rise post-fire. Evidence within this thesis identifies 350⁰C as a critical temperature whereby the explicit consideration of tendon creep does not significantly increase predicted prestress relaxation and subsequent UPT concrete slab deformation, compared to implicit creep consideration from Eurocode 2. The manufacturing standard to which prestressing steel tendon strands are produced has been shown experimentally by Gales to significantly influence their susceptibility to elevated temperature creep. This is reflected by Gales determining differing creep parameters as a function of stress for incorporation in Harmathy’s uniaxial creep strain function. Modelled prestress relaxation of isolated, tensioned and heated tendons within this thesis is therefore significantly reduced when tendons are manufactured to a yield stress of 1860MPa according to the BS 5896 standard, as opposed to the ASTM A416 standard. As a result Eurocode 2 determined stress-strain curves implicitly account for accumulated creep strain during heating, at 10⁰C per minute, up to approximately 400⁰C for grade 1860 ASTM A416 manufactured tendons and 500⁰C for grade 1860 BS 5896 standard tendons. The aforementioned critical temperature of 350⁰C does not in actuality apply to necessary explicit creep consideration for UPT concrete slabs modelled with grade 1860 BS 5896 standard tendons. This temperature however remains a design temperature limit, owing to the potential onset of microstructural recrystallization beyond 400⁰C and the associated degradation of mechanical properties that coincides. The reasons for such differing elevated temperature creep and stress relaxation behaviour between the two manufacturing standards of prestressing steel wires and strands has been postulated within this thesis to be due to differing chemical compositions. This relates specifically to large relative differences of phosphorus and sulphur found in wires manufactures to each standard as tested by Gales.

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, EC2, NBR, B3 e GL. O estudo da deformação do CAA também foi feito por meio da monitoração de uma viga protótipo protendida, seguida da comparação das deformações medidas com as obtidas por um programa de elementos finitos. A partir dos resultados experimentais, observa-se que dentre os modelos de previsão de fluência e retração estudados, o que mais se adéqua aos resultados obtidos experimentalmente, é o fornecido pelo ACI e GL. A utilização do modelo de previsão do ACI pelo programa de elementos finitos gerou bons resultados de previsão de deformações quando comparados com os resultados medidos. Em relação à função de fluência, nota-se que a norma brasileira é adequada para o concreto estudado. / Self-compacting concrete (SCC) is a new material and its mechanical properties have yet to be studied. It has a higher amount of mortar and smaller coarse aggregates which make it more deformable. On the other hand, the packing of the particles in fresh SCC and its larger strength (at a constant water/cement ratio) may act in the opposite way. Besides, the prediction models provided by the Brazilian Code do not take special concretes into account. The main objective of this work is to verify if the creep and shrinkage prediction models available in the literature can predict those properties of a SCC. This study involves aspects of its characterization by tests in laboratory of creep, shrinkage and other mechanical properties, such as compressive strength, splitting tensile strength and modulus of elasticity. For the creep test, the influence of environmental conditions (for specimens kept in an environment with and without temperature and humidity controlled) and age at loading were evaluated. From the obtained experimental results, a comparison was made to the values obtained from the ACI, EC2, NBR, B3 and GL prediction models. The deformability of SCC was analyzed by monitoring a post-tensioned beam prototype followed by the comparison of the measured deflection and strain long the time to those obtained from a finite element model. From the obtained experimental results of creep and shrinkage, the most adequate prediction models are the ACI and GL models. The use of the ACI model with the finite element method produced good results when compared to the experimental measurements of deflection and strain of the prototype beam. With respect to the compliance creep function, it can be noticed that the model provided by the Brazilian Code is adequate to the studied SCC.

This thesis aims to compare the cost of post-tensioned connection systems with conventional connections for the transferal of uplift forces in CLT stabilising walls. The desire for taller timber buildings has increased over time, in part due to environmental aspects but also to meet demands from an urbanizing population. For taller buildings, the horizontal load from wind increases. Due to timbers low self-weight, the uplifting force caused by the horizontal loading will be relatively large. Post-tensioning within timber structures is a non-conventional method for the transferal of uplifting forces that has been applied in only a few projects. The cost of the post-tensioning method is therefore unclear to the general engineer and has for that reason been investigated within this thesis. To gain information about the different aspects that might be affected by the connection method, interviews were held with different professionals who had worked with the post- tension method in timber structures. A cost comparison was performed for four different connection methods for stabilising walls, where the methods were three versions of the post-tension method and one with the more common angle brackets and hold-downs. The thesis was completed with a cost comparison within a case study, where the financial differences between the different connection methods for stabilising walls in a building were investigated. The case study building was based on a project currently being designed in Uppsala. Several different versions of the building were created, where the number of stories and stabilising walls of the building were changed. The connection costs for the different versions were compared to find the most cost-effective solution. The results from the stabilising wall analysis showed that the conventional connection method, was the cheaper option for stabilising walls of 4-storeys. While the post-tension method had a cheaper material cost for stabilising walls of 8-storeys and above. As the building height increased the post-tension systems became more priceworthy. The largest cost difference found between the conventional and the post-tension systems was for the 20-storey tall wall subjected to an uplift of 100 kN, where the conventional system was 76,5% more expensive than the most economical post-tensioning system. A four- storey interval was used for the analysis of the building heights. The results from the case study cost comparison followed in the same line as the results from the stabilising wall cost comparison. Both indicated that the post-tension systems became more economical compared to the angle brackets for increased building heights. / Syftet med detta examensarbete är att undersöka kostnaden för olika infästningsmetoder för stabiliserande väggar i träkonstruktioner. Fokus ligger på efterspänningsmetoden, som innebär att det monteras stänger i väggarna genom flera våningar som sedan spänns åt. Examensarbetet begränsas i att titta på byggnader uppförda i KL-trä. Det övergripande syftet med arbetet är att avgöra om efterspänningssystem är ett ekonomiskt lönsamt alternativ kontra konventionella infästningsmetoder, för att stabilisera KL-träväggar. KL-trä står för kors-limmat trä och används idag för bärande konstruktioner inom träbyggnader och består av flera lager träskivor som har limmats ihop. Varje lager har vridits med 90 grader i förhållande till det föregående, för att främja komponentens styrka och fuktmotstånd. För att samla information om de olika aspekter som påverkas av valet av infästningsmetod hölls intervjuer med personer som använt sig av efterspänningsmetod i träkonstruktioner. Utöver detta genomfördes även en kostnadsjämförelse mellan olika infästningsalternativ för olika stabiliserande väggar. De alternativ som jämfördes var efterspänningsmetoden och de mer konventionella vinkeljärnen. Resultaten från kostnadsjämförelsen visade att vinkeljärnen var det mest ekonomiska valet för byggnader i 4-våningar, medan materialkostnaden för efterspänningsmetoden var lägre för byggnader med 8-våningar och uppåt. Den största prisskillnaden mellan de två metoderna var för en vägg i en byggnad med 20 våningar och 100 kN i upplyftande krafter, där kostnaden av det konventionella systemet var 76,5% dyrare än det billigaste av de efterspända systemen. Analysen av byggnadshöjderna gjordes i intervaller om fyra våningar. Detta examensarbete avslutades med en fallstudie där de olika aspekterna som påverkar kostnaden av anslutningsmetod, som byggnadshöjd och planlösning, jämfördes. Resultaten från fallstudien följde i samma fotspår, då efterspänningsmetoden blev allt mer kostnadseffektiv med ökat våningsantal.

La presente tesis, expone inicialmente el atraso del Perú en cuanto al desarrollo de edificaciones en altura respecto al resto de países en la región sudamericana. Este hecho, junto al contexto de desarrollo del país, nos lleva a esperar que este tipo de proyectos se generen en los próximos años como landmarks en el país. Tomando en cuenta la suma de ambos conceptos, junto al factor sísmico al que el país está sometido constantemente, es que planteamos realizar el diseño de un edificio en altura, para ser tomado como una referencia dentro del marco de la normativa peruana. Para lograr esto, determinaremos los usos y requerimientos usuales de un edificio en altura, tomando como ejemplo otros edificios en altura de la región; las consideraciones a ser tomadas en cuenta en los criterios de estructuración, explorando el uso de un núcleo rígido central en edificaciones de este tipo; los factores del análisis estructural que pueden variar respecto al análisis de otro tipo de edificación; y el diseño estructural de los elementos resistentes que le dan solución a los esfuerzos generados por el análisis estructural, principalmente al diseño del núcleo rígido central y las losas postensadas. / his thesis initially exposes Peru's downside in the development of tall buildings comparing it to the rest of the countries in the South American. This fact, along with the country's development context, gives us hope that these type of projects will be generated in the up coming years as landmarks in the country. Taking into account the sum of both concepts, together with the seismic factor to which the country is constantly subjected, we propose to design a tall building, to be taken as a reference within the framework of Peruvian regulations. To achieve this, we will determine the usual uses and requirements of a tall building, taking as an example other tall buildings in the region; the considerations to be taken into account in the structuring criteria, exploring the use of rigid core walls in buildings of this type; the factors of the structural analysis that may vary depending on the analysis of another type of building; and the structural design of the resistant elements that provide a solution to the stresses generated by the structural analysis, mainly the design of the central rigid core and the post-tensioned slabs. / Tesis

During the fall of 2012, two separate Interstate 15 highway bridges over the 400 South roadway in Orem, Utah were demolished after 50 years of service. Four post-tensioned girders were salvaged from both the north-bound and south-bound bridge. A series of tests was performed with these girders in the System Material And Structural Health Laboratory (SMASH Lab). The girders were tested with different loading criteria to determine the strength and material properties of the girder. The experimental results were compared with the American Association of State Highway and Transportation Officials Load Resistance Factored Design (AASHTO LRFD) Bridge Design Specifications and a finite-element model using ANSYS. The AASHTO LRFD Specification was fairly conservative on predicting capacity and capable of predicting the type of failure that occurred. The ANSYS model was developed and calibrated to model the girder behavior. The concrete properties in the model were significantly adjusted in order to be comparable to the experimental results. Further exploration in ANSYS needs to be done to precisely model the actual behavior of the girder.

Accelerated Bridge Construction (ABC) techniques have resulted in innovative options that save time and money during the construction of bridges. One such group of techniques that has generated considerable interest is the usage of individual precast concrete members. Utilizing precast concrete decks allows for offsite curing, thus eliminating long delays due to formwork and concrete curing time. These precast concrete decks have inherent joints between the individual panels. These joints are locations for potential leakage, which can lead to corrosion or inadequate long-term performance. Post-tensioning the precast deck panels helps to eliminate leakage; however, conventional longitudinal post-tensioning systems require complete deck replacement in the event of a single faulty deck panel. A proposed post-tensioned, curved-strand connection allows for a single panel to be replaced. The capacity of the proposed curved-strand connection was investigated in order to compare its behavior to other systems that are currently in use. Tests were performed in composite negative bending, beam shear, and positive bending. The curved strand connection was found to behave similarly to the standard post-tensioning system in positive bending and shear. The curved-strand connection was found to be comparable to a standard post-tensioning system. The ultimate capacity of the curved-strand connection in negative bending was found to be 97% of the standard post-tensioning. Pre-stress losses were measured and predicted for the service life of the connection and were found to be 6% at the 75- year service life of a bridge.