No / In composite steel beams with precast hollow core slabs, the amount of transverse reinforcement can have a significant effect on the shear and slip capacity of the mechanical shear connectors. The issue of connector ductility becomes especially important when partial shear connection is adopted, as premature failure of the shear connectors would lead to sudden failure of the composite beam. This chapter presents its findings on the effect of transverse reinforcement on connector ductility and proposes design equations. Transverse reinforcement is used to provide ties for the slabs and confined concrete from splitting. The ductility of the shear connector, that is, slip capacity is directly affected by the amount of transverse reinforcement. Design equations presented in this chapter for estimating the shear capacity of the headed shear stud show a good correlation with the push-off test results. For full shear connection design, pre-splitting shear capacity of the headed stud can be used for the composite design, while for partial shear connection design, post-splitting shear capacity of the headed stud should be used. In general, a minimum transverse reinforcement of T16 bars should be used if partial shear connection design is used to ensure a minimum ductility of 6mm slip.

Corrosion of reinforcing steel is a major cause of damage to bridges in the United States. A possible solution to the corrosion issue is carbon fiber reinforced polymer (CFRP) material. CFRP material has been implemented as flexural reinforcement in many cases, but not as transverse reinforcing. The CFRP material studied in this thesis was NEFMAC grid, which consists of vertical and horizontal CFRP tows that form an 8 in. by 10 in. grid. The use of NEFMAC grid as transverse reinforcing has not been previously investigated. First, the development length of NEFMAC grid was determined. Next, an 18 ft long 19 in. deep beam, modeled after prestressed Bulb-T beams, was created with NEFMAC grid reinforcement. The beam was loaded with a single point load near the support to induce shear failure. Beams were fitted with instrumentation to capture shear cracking data. Shear capacity calculations following four methods were compared to test results. Lastly, a parametric study with strut-and-tie modeling was performed on Precast Bulb-T (PCBT) girders to determine the amount of CFRP grid needed for reinforcement in the anchorage zone. This thesis concludes that NEFMAC grid is a viable shear design option and presents the initial recommendations for design methods. These methods provide a basis for the design of NEFMAC grid shear reinforcing that could be used as a starting point for future testing of full scale specimens. When designing with NEFMAC grid, the full manufacturer's guaranteed strength should be used as it is the average reduced by three standard deviations. AASHTO modified compression field theory provides the best prediction of shear capacity. For anchorage zone design, working stress limits for CFRP grids need to be increased to allow more of the strength to be implemented in design. / Master of Science

Corrosion of reinforcing steel causes shorter life spans in bridges throughout the United States. The use of carbon fiber reinforced polymer (CFRP) materials as the flexural reinforcement in bridge girders has been extensively studied. However, CFRP transverse reinforcement has not been as rigorously investigated, and many studies have focused on CFCC stirrups. The use of C-Grid as an option for transverse reinforcing has not been previously investigated. This thesis concludes that C-Grid is a viable shear design option and presents the initial recommendations for design methods. These methods provide a basis for the design of C-Grid shear reinforcing that could be used as a starting point for future testing of full scale specimens. This testing program first determined the mechanical properties of C-Grid and its development length. Four 18 ft long 19 in. deep beams, modeled after prestressed Bulb-T beams, were created to test the C-Grid, as well as steel and CFCC stirrups. The beams were loaded with a single point load closer to one end to create a larger shear load for a given flexural moment. Overall beam displacement was measured to determine when flexural reinforcement yielding was reached, and beams were fitted with rosettes and instrumentation to capture initiation of shear cracking. Shear capacity calculations following four methods were compared to test results. The design method should follow the AASHTO modified compression field theory with equations for β and θ. The manufacturer's guaranteed strength should be used for design as long as that strength is the average reduced by three standard deviations. Shear crack widths are controlled to a similar size as steel stirrups when using at least two layers of grid. / Master of Science

As vigas mistas de aço-concreto vêm ganhando espaço no mundo e no Brasil. Sua grande vantagem é o aproveitamento das melhores propriedades que cada material apresenta. O aço possui excelente resposta para esforços tanto de tração como os de compressão e o concreto para esforços de compressão. As vigas mistas envolvem basicamente o perfil de aço, a laje de concreto, os conectores e as armaduras. Na interface destes materiais ocorrem fenômenos que merecem destaque, como grau de interação, cisalhamento na superfície de contato e separação vertical. Os procedimentos normalmente empregados em projetos de estruturas convencionais de concreto armado e de aço fornecem muitas respostas para questões semelhantes nas estruturas mistas, porém, no geral, não abordam a questão mais relevante que é a ligação entre o aço e o concreto. Na vizinhança dos conectores de cisalhamento, a laje da viga mista de aço e concreto está sujeita a uma combinação de cisalhamento longitudinal e momento fletor transversal, por isso a interface é a região que necessita de uma análise cuidadosa. Esses aspectos são os objetos principais da pesquisa. Adicionalmente são discutidos os procedimentos de projetos adotados pelas normas brasileira (NBR 8800-86), americana (AISC) e européia (EUROCODE 4): nas regiões de ligações entre os materiais por meio de conectores em perfis de aço sob lajes de concreto, no controle da fissuração em seções solicitadas por momentos negativos e nas armaduras transversais de costura. / The use of composite steel-concrete beams is increasing in Brazil and in the world, because this is to take advantage of the best properties of each material. Steel has an excellent response to compression and tension and concrete has to compression. Composite beams include basically the steel beam, concrete slab, connectors and reinforcement. Some phenomena in the interface of these materials must be considered, like the degree of interaction, shear in contact surface and uplift. The procedures normally taken in design of conventional structures of reinforced concrete and steel structures supply many answers to similar questions in composite structures, but, in general, they do not approach the most relevant question which is the bond between steel and concrete. The slab of composite steel-concrete beam is affected by a combination of longitudinal shear and transverse flexure, in the neighborhood of the shear connector. The analysis of the behavior of the slab and the reinforcement are main aspect of the work. In addition, some design procedures adopted by Brazilian Standard (NBR 8800-86), American Standard (AISC-2005) and European standard (EUROCODE 4) are discussed, in especial the related to connects, the crack control in sections with hogging moment and in transverse reinforcement.

A previously completed study in the field of concrete block construction by Ahmed and Feldman (2012) indicated that, on average, the reinforcing bars in non-contact lap splices, where the lapped bars are located in adjacent cells, only develop 71% of the tensile resistance of spliced bars which are in contact. An experimental program was therefore initiated to design and evaluate remedial measures which can potentially increase the tensile resistance of non-contact lap splices to that of contact lap splice of the same lap length. Implementation of the proposed measures in various field situations was also analyzed. Six unique remedial splice details, along with standard contact and unaltered non-contact lap splices were evaluated and compared. The mitigative details included providing additional confinement, installing knock-out webs, placing splice reinforcement between the lapped bars, and combinations of these aforementioned details. Three replicates of each splice detail were constructed for a total of 24 wall splice specimens. Each wall splice specimen was reinforced with No. 15 Grade 400 deformed steel reinforcing bars with 200 mm lap splice lengths at located the midspan. The specimens were tested in a horizontal position under a monotonic, four-point loading geometry. Load and deflection data were collected throughout testing and were subsequently used in an iterative moment-curvature analysis to calculate the maximum tensile resistance of the spliced reinforcement. This was then used to compare the structural performance of each remedial splice detail to the standard contact and non-contact lap splices. The wall splice specimens which contained non-contact lap splices with knock-out webs, s-shaped, and transverse reinforcement in the splice region achieved similar tensile capacities as the wall splice specimens with standard contact lap splices. Industry professionals have indicated that the installation of the remedial measures evaluated in this study would not affect the constructability of masonry assemblages in field situations. The splice detail with knock-out webs confined within the lap splice length was determined to be the most viable procedure as it can be installed to increase the resistance of non-contact lap splices in almost all construction situations. This remedial procedure was able to improve the tensile resistance of the lapped reinforcement by 63% compared to the wall splice specimens with standard non-contact lap splices.

As vigas mistas de aço-concreto vêm ganhando espaço no mundo e no Brasil. Sua grande vantagem é o aproveitamento das melhores propriedades que cada material apresenta. O aço possui excelente resposta para esforços tanto de tração como os de compressão e o concreto para esforços de compressão. As vigas mistas envolvem basicamente o perfil de aço, a laje de concreto, os conectores e as armaduras. Na interface destes materiais ocorrem fenômenos que merecem destaque, como grau de interação, cisalhamento na superfície de contato e separação vertical. Os procedimentos normalmente empregados em projetos de estruturas convencionais de concreto armado e de aço fornecem muitas respostas para questões semelhantes nas estruturas mistas, porém, no geral, não abordam a questão mais relevante que é a ligação entre o aço e o concreto. Na vizinhança dos conectores de cisalhamento, a laje da viga mista de aço e concreto está sujeita a uma combinação de cisalhamento longitudinal e momento fletor transversal, por isso a interface é a região que necessita de uma análise cuidadosa. Esses aspectos são os objetos principais da pesquisa. Adicionalmente são discutidos os procedimentos de projetos adotados pelas normas brasileira (NBR 8800-86), americana (AISC) e européia (EUROCODE 4): nas regiões de ligações entre os materiais por meio de conectores em perfis de aço sob lajes de concreto, no controle da fissuração em seções solicitadas por momentos negativos e nas armaduras transversais de costura. / The use of composite steel-concrete beams is increasing in Brazil and in the world, because this is to take advantage of the best properties of each material. Steel has an excellent response to compression and tension and concrete has to compression. Composite beams include basically the steel beam, concrete slab, connectors and reinforcement. Some phenomena in the interface of these materials must be considered, like the degree of interaction, shear in contact surface and uplift. The procedures normally taken in design of conventional structures of reinforced concrete and steel structures supply many answers to similar questions in composite structures, but, in general, they do not approach the most relevant question which is the bond between steel and concrete. The slab of composite steel-concrete beam is affected by a combination of longitudinal shear and transverse flexure, in the neighborhood of the shear connector. The analysis of the behavior of the slab and the reinforcement are main aspect of the work. In addition, some design procedures adopted by Brazilian Standard (NBR 8800-86), American Standard (AISC-2005) and European standard (EUROCODE 4) are discussed, in especial the related to connects, the crack control in sections with hogging moment and in transverse reinforcement.

no / Precast concrete floors are widely used in building construction, but there is little detailed design guidance on their application in steel-framed buildings. Traditionally the steel beams have been designed to support the precast slabs on their top flange. However, there are an increasing number of composite frames and slim floor constructions where the precast slabs are designed to interact structurally with the steel frame. Composite action can be developed by welded shear connectors attached to the steel beams and by transverse reinforcement; however, this form of construction is currently outside the provisions of the current codes of practice. This paper discusses some of the particular issues that affect this form of construction, and presents design guidance using the Eurocode methodology.

Longitudinal slab splitting in composite hot rolled girders and joist girders was investigated. Two different type of framing configurations were studied with two tests conducted per configuration. The framing configurations were designated as either flush-framed or haunched, which describes the framing of the joists into the joist girders or H-shape. Each floor system consisted of at least one exterior or spandrel joist girder, one interior joist girder, and in three of the four tests, an exterior or spandrel H-shape. The nominal lengths of the girders were 30 ft 4 in. with a centerline spacing of 7 ft for the flush-framed tests and 6 ft 9 in. for the haunch tests. Varying amounts of transverse reinforcement were used in the slab over each girder. Shear connectors were all 0.75 in. diameter headed shear studs of varying lengths. The results of these tests were used to determine the minimum amount of transverse reinforcement required to prevent longitudinal splitting from controlling the strength of the section. A comparative analytical study was performed to generate a design procedure for determining the appropriate amount of transverse reinforcement. This consisted of adapting existing procedures in reinforced concrete for similar shear problems and generating alternative procedures based on existing research for composite construction. Results from these methods were then calibrated against experimental data obtained in this study. / Master of Science

Closure joints are used in precast bridge construction to join two pieces of precast concrete. The pieces of concrete are joined by a lap splice which consists of longitudinal steel sticking out of each precast element and overlapped over the minimum required development length. State departments of transportation find it desirable to make the width of closure joints short. To achieve this, bridge engineers have been using hooked bars in the closure joints in lieu of straight bars, with the assumption that this would allow for shorter splice lengths. Though engineers in practice are doing this, design guidance does not exist. One research project by Coleman (2024) tested 58 beam-splice specimens to investigate the impacts of a variety of parameters on bond and anchorage and develop design guidance for hooked bar lap splices. This project did not investigate three parameters: the number of lap splices, the placement of transverse reinforcement, and the addition of steel fibers in the closure joint. For this thesis, 15 beam-splice specimens were tested in 4 point-bending to investigate the impact of these parameters on bond and validate the descriptive equation developed by Coleman (2024) to determine the bar stress of a hooked bar lap splice. The findings of this study suggest that the number of splices and the placement of transverse reinforcement has minimal impact on the bar stress developed, and the equation by Coleman (2024) adequately predicts the bar stress when these parameters were varied. The addition of steel fibers to the closure joint had a substantial impact on increasing the splice strength. In the beams where steel fibers were added in a 1% fiber volume fraction, the descriptive equation by Coleman (2024) underpredicted the bar stress for both unconfined and confined beams with the addition of fibers. Thus, this thesis proposes a factor to multiply the descriptive equation by determining the bar stress when steel fibers are added. With these findings, using steel fibers in closure joints for precast concrete can be used to reduce splice length in non-contact hooked bar lap splices. / Master of Science / Precast concrete is concrete that is cast off-site in a controlled environment and transported to the site to then be put together at the site of a project. In bridge construction, this is very beneficial to projects since it means that there is more quality control of the specimens and can allow for faster construction times since the components can have time to cure to strength off-site. To put together pieces of precast concrete to create continuous beams and other components, a closure joint is used. These closure joints consist of two precast pieces of concrete which have longitudinal steel sticking out of each precast element. The pieces of concrete are then joined by overlapping the longitudinal steel in a lap splice. Where a lap splice is used to develop the minimum development, length is required to provide the adequate bar strength such that load will be transferred from one beam to another to create a continuous beam. State departments of transportation find it desirable to make the width of closure joints short. Since closure joint width is typically controlled by the minimum development length required to connect the pieces of concrete, the main way to reduce the width is to reduce the minimum development length. To achieve this, bridge engineers have been using hooked bars in the closure joints in lieu of straight bars, with the assumption that this would allow for shorter splice lengths. Though engineers in practice are doing this, design guidance does not exist. One research project by Coleman (2024) tested 58 beam-splice specimens to investigate the impacts of a variety of parameters on bond and anchorage and develop design guidance for hooked bar lap splices. This project did not investigate three parameters: the number of lap splices, the placement of transverse reinforcement, and the addition of steel fibers in the closure joint. For this thesis, 15 beam-splice specimens were tested in 4 point-bending to investigate the impact of these parameters on bond and validate the descriptive equation developed by Coleman (2024) to determine the bar stress of a hooked bar lap splice. The findings of this study suggest that the number of splices and the placement of transverse reinforcement has minimal impact on the bar stress developed, and the equation by Coleman (2024) adequately predicts the bar stress when these parameters were varied. The addition of steel fibers to the closure joint had a substantial impact on increasing the splice strength. In the beams where steel fibers were added in a 1% fiber volume fraction, the descriptive equation by Coleman (2024) underpredicted the bar stress for both unconfined and confined beams with the addition of fibers. Thus, this thesis proposes a factor to multiply the descriptive equation by determining the bar stress when steel fibers are added. With these findings, using steel fibers in closure joints for precast concrete can be used to reduce splice length in non-contact hooked bar lap splices.

[pt] Neste trabalho é feito o estudo da influência do cobrimento da armadura longitudinal e dos grampos suplementares na resistência de pilares de concreto submetidos à compressão excêntrica. Para este fim foram ensaiados pilares curtos, com armadura longitudinal contínua e pilares com emenda na armadura. Foi elaborado um modelo para o cálculo da distribuição da tensão normal e da tensão de aderência nas barras de emendas comprimidas que reproduziu bem o verificado experimentalmente. Mostra-se a importância da tensão de ponta na transmissão de forças na emenda. Se alerta sobre como a técnica normalmente empregada no reparo dos pilares onde as armaduras apresentam corrosão, que consiste na retirada parcial ou total do que restou do cobrimento para o tratamento e/ou substituição da armadura, e posterior reposição da camada de cobrimento, pode levar a ruptura do elemento por perda de aderência. Mostra-se como não colocar os grampos suplementares pode levar a perda da estabilidade do elemento. / [en] In this work, the influence of the longitudinal reinforcement cover and supplementary transversal reinforcement on the ultimate strength of the concrete columns under eccentric compression is studied. For this purpose, tests on short columns with continuum and lapped spliced bars were carried out. A theoretical model for the calculation of the stress and bond distributions on the splice length is proposed and tested with the experimental data of this work, showing a good agreement. The relevance of the end bearing effect on the transmission of the forces in the splice is shown. An alert again the usual technique used to repair the corroded bars inside the column, i.e., to remove partially or totally the remaining concrete cover to treat or substitute the damaged reinforcement bars, and lately to put back the concrete cover. This technique may provide the element failure by the lost of bond between the remaining concrete surface and reinforcement bars. It is shown how the absence of supplementary transversal reinforcement can lead to the instability of column.