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The strength and behavior of composite slabs are governed by the shear interaction between the concrete and the steel deck. The interaction property depends on several factors and it is not possible to express the relationship from a purely analytical basis. As such, analysis and design methods available today use the interaction property derived from full scale performance tests. In numerical modeling, the interaction property is obtained from a variety of elemental push off tests which, for the most part, do not represent actual slab bending. This research comprises experimental, analytical and numerical investigations of composite slabs. The central objective of the experimental work is to develop a new small scale test method for evaluating the performance and behavior of composite slabs and also for determining the shear interaction property for use in numerical analysis. The characteristics of the new test specimen are simple, easy and economical to conduct, as well as comparable in performance and behavior with the more common full slab test. The analytical study was conducted to determine whether data from small scale tests can be used in the present analytical methods to predict the strength of the actual slabs, to use the same test data for input in the numerical analysis, and to improve the present Partial Shear Connection (PSC) design procedure. A model that relates the shear bond stress to slab slenderness, which can be used to estimate the shear interaction property for slabs with any slenderness, was developed. Finally, a finite element study was conducted to develop a simple modeling method that is suitable for analyzing composite slabs with variable slenderness. Parametric analyses to determine the effect of slenderness on the performance and behavior of composite slabs, and on the accuracy of the present design methods were also conducted. The results of this investigation demonstrate that the small scale test is feasible as a replacement for the full scale test. Data from the small scale test can be used not only in the analytical methods but also in the numerical analysis, thus eliminating the need for separate push off type tests. / Ph. D.

No / In steel¿concrete composite beams, the longitudinal shear force is transferred across the steel flange/concrete slab interface by the mechanical action of the shear connectors. The ability of the shear connectors to transfer these longitudinal shear forces depends on their strength, and also on the resistance of the concrete slab against longitudinal cracking induced by the high concentration of shear force. Most of the research in composite construction has concentrated on the more traditional reinforced concrete and metal deck construction, and little information is given on shear capacity of the headed studs in precast hollowcore slabs. In this paper, a standard push test procedure for use with composite beams with precast hollowcore slabs is proposed. Seven exploratory push tests were carried out on headed studs in solid RC slabs to validate the testing procedures, and the results showed that the new test is compatible with the results specified in the codes of practice for solid RC slabs. Once a standard procedure is established, 72 full-scale push tests on headed studs in hollowcore slabs were performed to determine the capacities of the headed stud connectors in precast hollowcore slabs and the results of the experimental study are analysed and findings on the effect of all the parameters on connectors¿ strength and ductility are presented. Newly proposed design equations for calculating the shear connectors¿ capacity for this form of composite construction are also be given.

Yes / This paper describes a sequence of experiments on a long-span asymmetric composite cellular beam. This type of beam has become very popular, combining the composite action between the steel and concrete with the increased section depth, compared with more commonly used solid-web I sections. Openings in the steel web also reduce the self-weight and can accommodate the passage of service ducts. Eurocode 4 recommends a high degree of shear connection for asymmetric composite beams despite the practical difficulties in achieving this. Recent research suggests that the required degree of shear connection could be reduced, particularly for beams that are unpropped during construction. However, little test data exists to verify the behaviour of unpropped composite cellular beams. Therefore two series of tests were conducted on a 15.26 m long asymmetric composite cellular beam with regular circular openings and an elongated opening at the mid-span. The degree of shear connection was 36%, less than half of that recommended in Eurocode 4, and the beam was unpropped during construction. The beam was subjected to uniformly distributed loading and shear load during the tests. The end-slip, mid-span vertical deflection, shear connector capacity and strain distribution were examined. The beam failed at an applied uniform load of 17.2 kN/m2 (3.4 × design working load 5.0 kN/m2). The member withstood an applied shear load that was 45% higher than predicted, and exhibited a Vierendeel mechanism at the elongated opening. Overall, these tests demonstrated the potential of unpropped composite cellular beams with low degrees of shear connection. / RFCS

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No. of bitstreams: 2 Dissertação - Vanessa Elizabeth dos Santos Borges - 2012.pdf: 14072419 bytes, checksum: a1a40d9889226694c5d95e512ec5a689 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2012-08-21 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Currently, the civil construction industry has presented some changes. This is due to the recent economic growth that Brazil had achieved. These changes increased the employment of precast concrete structures. The front of this, some studies about the precast concrete connections had been developed. This work objective was to study the shear stress transference mechanism, which appears in the beam-slab connection interface – the composite beams. It was tested three different roughness degrees of the slab shear pockets: naturally rough surface, intentionally rough surface and surface with shear-key. For this, push-out tests – double “L” – were carried out and they showed that the employment of surface setting retarder admixture (ARSP) achieves the roughness degree recommended by the NBR 9062 (ABNT, 2006) without significantly reduce the connection strength. Next, with the same model type, the influence of the percentage of steel across the joint above the strength connection was tested. Besides, another model type – three blocks – was carried out with the same aim. Through those tests, It was could ascertained that the increase of the percentage of steel across the joint provides a linear increase of the strength connection, in as much as, the minimum and maximum values were inspected. Furthermore, the double “L” tests allowed the proposition of two expressions to determine the strength shear connection. And, in a third moment, composite beams were carried out, the results indicated, for the roughness degree and percentage of steel across the joint tested, that the beam-slab connection presents a partial interaction degree, even as the connection degree. Ultimately, the similarity between the three different types of tests could be proved with the proposed expressions application in the tests results. / A indústria da construção civil, no Brasil, tem passado por alterações nos últimos anos. Tal fenômeno deve-se ao atual crescimento econômico atingido pelo país. Como resultado dessas alterações, aumentou o emprego das estruturas pré-moldadas de concreto. Diante desse contexto, têm sido realizados estudos sobre ligações entre peças pré-moldadas. Este trabalho apresenta como objetivo o estudo dos mecanismos de transferência das tensões de cisalhamento que se formam na interface entre vigas e lajes pré-moldadas, as chamadas vigas compostas. Foram avaliados, por meio de ensaios de cisalhamento direto em modelos compostos por duas peças em formato de “L”, três diferentes níveis de rugosidade da interface entre as peças, quais sejam: superfície naturalmente rugosa, superfície intencionalmente rugosa e superfície com chaves de cisalhamento. Dessa avaliação da rugosidade, constatou-se ser possível garantir o nível mínimo de rugosidade estabelecido pela NBR 9062 (ABNT, 2006) com o emprego de um aditivo retardador de pega superficial (ARSP), não apresentando redução significativa na resistência da ligação. Posteriormente, foram realizados ensaios utilizando o mesmo modelo, nos quais foi avaliada a influência da taxa de armadura normal à interface, que variou de 0,19% a 1,2%, sobre a resistência ao cisalhamento da ligação. E, paralelamente a esses ensaios, modelos do tipo três blocos ligados por meio de nichos, também com presença de armadura normal à superfície de cisalhamento, com taxas de 0,5% a 1,2%, foram testados e comparados com os anteriores. Tais ensaios permitiram a constatação de que ao se aumentar o valor da taxa de armadura, aumenta-se linearmente a resistência ao cisalhamento da ligação, ressaltando-se a necessidade de verificação de um valor mínimo e um máximo. E, além disso, os ensaios do tipo duplo “L” permitiram a proposição de expressões para cálculo da resistência ao cisalhamento da ligação. Em um terceiro momento, ensaios em vigas compostas formadas por viga e laje pré-moldadas ligadas mediante nichos com superfícies tratadas com ARSP foram realizados. Esta etapa visava à confirmação da eficiência da ligação com nichos e conectores metálicos. Quanto aos ensaios das vigas compostas, estes mostraram que para o nível de rugosidade avaliada e as taxas de armadura adotadas o grau de interação entre as peças é parcial, assim como seu grau de conexão. No que diz respeito à forma de ruptura observada nas vigas compostas, assim como nos modelos de cisalhamento direto, pode-se sugerir que o tratamento da interface na região dos nichos não proporcionou rugosidade suficiente para que houvesse uma ligação mais resistente entre as peças. E, por fim, da aplicação das expressões aos resultados dos ensaios de três blocos e de vigas constatou-se que há representatividade entre os três tipos de ensaio realizados.

A common bridge type is the steel-concrete bridge where the concrete deck is built over steel girders. In many earlier designs the bridge type was often built as non-composite, which means that the concrete deck and the steel girder has no shear connection at the steel-concrete interface and therefore bend as individual components. With the increased traffic loads of today some of the existing non-composite bridges have insufficient bending capacity, and therefore they must either be replaced or strengthened. To replace a bridge and construct a new one has many downsides, it is time consuming, expensive, and it consumes a lot of finite resources. Therefore, it is better if the bridges could be strengthened instead. Non-composite steel-concrete bridges can in some cases be strengthened by installing shear connectors that enable composite action between the concrete deck and steel girder. To enable full composite action, many shear connectors need to be installed (10-15 per meter). In some cases, full composite action is not needed to achieve a sufficient load capacity. Therefore, to save time and money and reduce material usage, it could be favourable if the amount of shear connectors could be lowered. The concept of using less shear connectors than required for full composite action is known as partial composite action and is defined as a ratio η that can vary between 0 and 1,0. If the ratio is 0, the structure is non-composite and if it is 1,0, it is fully composite. For every ratio between, the structure is partially composite. Partial composite action is not allowed by the standard for new composite bridges in Europe, EN 1994-2, which instead requires full composite action for new bridges. Since the conventional shear connector type, Welded Headed Stud (WHS) is impractical for post-installation this can yield large costs. This thesis therefore analyses the efficiency of strengthening non-composite bridges with partial composite action by post-installation of the shear connector type Coiled Spring Pins (CSPs), which is more suitable for post-installation compared to WHS since the installation can be made from underneath the bridge deck. The thesis consists of a theoretical study about composite action with a focus on partial composite action. In addition to the theoretical study, a case study is performed on an existing non-composite steel-concrete bridge, the bridge over Yxlö channel, which is situated south of Stockholm in Nynäshamn municipality. In the case study, hand-calculations to calculate the moment capacity for the bridge and the bending stresses in the bridge is made. In addition, a linear Finite Element-analysis (FE-Analysis) is made to evaluate the bending stresses in the cross-section. Further, in the FE-analysis, the horizontal slip and shear flow at the steel-concrete interface is evaluated. The calculations in the case study are made for 10 different degrees of shear connection from 0 - 1,0 with increments of 0,1. The results from the hand-calculations showed that partial composite action an efficient strengthening method, especially for lower degrees of shear connection. The moment capacity in the mid-section of the bridge could be increased between 16 and 41 % for shear connection ratios between 0,4 and 1,0, when applying plastic properties. If elastic properties were used, the increase in moment capacity for the same interval and section was 13 – 21 %, which shows that if it is possible to use plastic properties, the moment capacity could be increased more.  The results from the stress analysis in both the Hand- and FE-calculations showed that the stresses were reduced efficiently, especially for the top flange of the steel girder, where the stresses reduced 75-85 % for shear connection ratios between 0,4 & 1,0. The reduction of the stresses in the bottom flange were not as efficient, but still a reduction of 15 – 20 % is possible for shear connection ratio between 0,4 – 1,0. The overall conclusion from the thesis is that partial composite action can be an efficient strengthening method, and that non-composite bridges like the Yxlö Bridge could be strengthened with CSPs and have an effective increase of the bending moment capacity. This way the allowed axle- and bogie load on the bridge could be increased which could extend the technical life length of the bridge and reduce the need for new bridges.

Neste trabalho, foram estudadas as vigas compostas formadas por viga e laje pré-moldadas de concreto. A ligação empregada na interface era constituída por conectores metálicos associados com concreto moldado no local. Os conectores eram formados por vergalhões de aço dobrados em forma de laço, que eram inseridos em nichos existentes na laje pré-moldada. A ligação era realizada preenchendo os nichos com concreto de alto desempenho. O objetivo foi caracterizar a ligação viga-laje e analisar o comportamento à flexão das vigas compostas com laje pré-moldada. Foram realizados ensaios de cisalhamento direto sob carregamento monotônico, tendo sido observados aumentos de 250% na resistência da ligação devido à substituição da ligação plana e lisa por outra com chave de cisalhamento. A partir desses ensaios, foi proposto um modelo analítico para representar o comportamento das ligações com chave de cisalhamento, considerando a influência da resistência do concreto, do diâmetro do conector e da adição de fibras metálicas à ligação. Foram realizados ensaios de cisalhamento direto com carregamento cíclico não reversível, tendo sido observado menores perdas de rigidez na ligação devido à adição de fibras. Os resultados de ensaios em vigas mostraram que a resistência à flexão da viga composta está diretamente relacionada com a resistência ao cisalhamento da interface. O dimensionamento adequado da interface garantiu à viga composta com laje pré-moldada um comportamento semelhante ao das vigas com laje moldada no local. Dessa forma, esse sistema apresenta-se como uma alternativa viável ao sistema com laje moldada no local. / Composite beams formed by precast beam and precast deck were studied in this work. The connection used in the interface was constituted by steel connectors associated with cast-in-place concrete. Steel bars bent in hoop form constituted the connectors, which were inserted in shear pockets in the precast deck. The connection was carried out filling the shear pockets with high performance concrete. The objective was to characterize the beam-deck connection and to analyze the flexural behavior of the composite beams with precast deck. Push-out tests with monotonic loading were carried out, and it was observed an increase of 250% in the shear strength of the connection due to the substitution of the plane smooth surface for other with shear-key. Based on these tests, an analytic model to represent the behavior of the connections with shear-key was proposed, considering the influence of the strength of the cast-in-place concrete, the diameter of the connector and the addition of steel fibers to the connection. Push-out tests with no reversible cyclic loading were carried out, and it was observed lower shear stiffness degradation in the connection due to the addition of fibers. The results of beam tests showed that the flexural strength of the composite beam is directly related to the shear strength of the interface. The appropriate design of the interface guaranteed to the composite beam with precast deck a flexural behavior similar to the beams with cast-in-place deck. In that way, the system with precast deck is a viable alternative to the system with cast-in-pace deck.

Neste trabalho, foram estudadas as vigas compostas formadas por viga e laje pré-moldadas de concreto. A ligação empregada na interface era constituída por conectores metálicos associados com concreto moldado no local. Os conectores eram formados por vergalhões de aço dobrados em forma de laço, que eram inseridos em nichos existentes na laje pré-moldada. A ligação era realizada preenchendo os nichos com concreto de alto desempenho. O objetivo foi caracterizar a ligação viga-laje e analisar o comportamento à flexão das vigas compostas com laje pré-moldada. Foram realizados ensaios de cisalhamento direto sob carregamento monotônico, tendo sido observados aumentos de 250% na resistência da ligação devido à substituição da ligação plana e lisa por outra com chave de cisalhamento. A partir desses ensaios, foi proposto um modelo analítico para representar o comportamento das ligações com chave de cisalhamento, considerando a influência da resistência do concreto, do diâmetro do conector e da adição de fibras metálicas à ligação. Foram realizados ensaios de cisalhamento direto com carregamento cíclico não reversível, tendo sido observado menores perdas de rigidez na ligação devido à adição de fibras. Os resultados de ensaios em vigas mostraram que a resistência à flexão da viga composta está diretamente relacionada com a resistência ao cisalhamento da interface. O dimensionamento adequado da interface garantiu à viga composta com laje pré-moldada um comportamento semelhante ao das vigas com laje moldada no local. Dessa forma, esse sistema apresenta-se como uma alternativa viável ao sistema com laje moldada no local. / Composite beams formed by precast beam and precast deck were studied in this work. The connection used in the interface was constituted by steel connectors associated with cast-in-place concrete. Steel bars bent in hoop form constituted the connectors, which were inserted in shear pockets in the precast deck. The connection was carried out filling the shear pockets with high performance concrete. The objective was to characterize the beam-deck connection and to analyze the flexural behavior of the composite beams with precast deck. Push-out tests with monotonic loading were carried out, and it was observed an increase of 250% in the shear strength of the connection due to the substitution of the plane smooth surface for other with shear-key. Based on these tests, an analytic model to represent the behavior of the connections with shear-key was proposed, considering the influence of the strength of the cast-in-place concrete, the diameter of the connector and the addition of steel fibers to the connection. Push-out tests with no reversible cyclic loading were carried out, and it was observed lower shear stiffness degradation in the connection due to the addition of fibers. The results of beam tests showed that the flexural strength of the composite beam is directly related to the shear strength of the interface. The appropriate design of the interface guaranteed to the composite beam with precast deck a flexural behavior similar to the beams with cast-in-place deck. In that way, the system with precast deck is a viable alternative to the system with cast-in-pace deck.

This paper presents a numerical investigation into the behaviour of headed shear stud in composite beams with profiled metal decking. A three-dimensional finite element model was developed using general purpose finite element program ABAQUS to study the behaviour of through-deck welded shear stud in the composite slabs with trapezoidal deck ribs oriented perpendicular to the beam. Both static and dynamic procedures were investigated using Drucker Prager model and Concrete Damaged Plasticity model respectively. In the dynamic procedure using ABAQUS/Explicit, the push test specimens were loaded slowly to eliminate significant inertia effects to obtain a static solution. The capacity of shear connector, load-slip behaviour and failure modes were predicted and validated against experimental results. The delamination of the profiled decking from concrete slab was captured in the numerical analysis which was observed in the experiments. ABAQUS/Explicit was found to be particularly suitable for modelling post-failure behaviour and the contact interaction between profiled decking and concrete slabs. It is concluded that this model represents the true behaviour of the headed shear stud in composite beams with profiled decking in terms of the shear connection capacity, load-slip behaviour and failure modes.