Yes / To investigate the flexural performance of steel-UHPC (ultra-high performance concrete) composite beams with welded steel shear keys (SSK), eight specimens were experimental studied by four-point bending test. The finite element (FE) models were established based on the experimental results, then, the failure mode, load, deflection, strain and relative interface slip were parametric analyzed. The influences of strength, dimensions and configuration of upper concrete slab, steel beams as well as SSK on flexural performance, in terms of load-deflection response, ductility and ultimate energy dissipation, were studied. The experimental results show that steel-UHPC composite beams have superior bearing capacity, deformation capacity, ductility and energy dissipation ability when compared with steel-NSC (normal strength concrete) composite counterparts. Increasing the height of upper concrete slab has a significant effect on improving bending capacity and flexural stiffness, while increasing the width has a significant effect on enhancing deformation, ductility and ultimate energy dissipation. Increasing the yield strength, thickness of web and flange of steel beams has significant effect on improving bending capacity. Reducing the SSK spacing or increasing the yield strength of SSK, height and thickness slightly improve the cracking, yield and ultimate loads, reduce deflections, enhance the flexural stiffness, slightly weakens the ductility and ultimate energy dissipation. Besides, four types of failure modes were defined, based on reasonable assumptions, formulae for bearing capacity were proposed, and the predicted results fit well with experimental results. The results can be taken as reference for the design and application of steel-UHPC composite beams in long-span and heavy-load structures. / The authors would like to acknowledge the financial support to the work by the Natural Science Foundation of Jiangsu Province, China (BK20201436), High-End Foreign Experts Project of Ministry of Science and Technology, China (G2022014054L), Science and Technology Project of Jiangsu Construction System (2021ZD06, 2018ZD047), Science and Technology Cooperation Fund Project of Yangzhou City and Yangzhou University (YZU212105, YZ2022194), Science and Technology Project of Yangzhou Construction System (202309, 202312, 202204).

Este trabalho apresenta uma análise teórico-experimental da ligação pilar-fundação por meio de cálice em estruturas de concreto pré-moldado, com ênfase no colarinho. No programa experimental, foram ensaiados cinco protótipos sob força normal com grande excentricidade, variando-se o tipo e condição de interface: três com interface lisa, onde em dois foi eliminada a adesão para representar a situação mais adequada de projeto; e dois com interface rugosa, com duas configurações diferentes de chaves de cisalhamento. Foram realizadas simulações numéricas pelo método dos elementos finitos nos modelos lisos sem adesão, com as não-linearidades físicas e de contato, e nos cálices rugosos, considerando-se a não-linearidade física e a aderência perfeita das interfaces. Os resultados experimentais indicaram a necessidade de se reavaliar os principais métodos de projeto para essa ligação. Desta forma, foi proposto, para o cálice liso, um modelo de projeto considerando o atrito entre as interfaces e o cálculo das paredes longitudinais como consolos. Já para o cálice com interface rugosa, como foi verificada a proximidade do comportamento dos modelos físicos rugosos com uma ligação monolítica, recomendou-se o dimensionamento de suas armaduras verticais, admitindo a transferência total dos esforços, e das armaduras horizontais superiores também com o funcionamento das paredes longitudinais como consolos. Os modelos numéricos apresentaram uma boa convergência e semelhanças na fissuração e no caminho de tensões em relação aos protótipos físicos, apesar das deformações terem sido menores que as observadas experimentalmente. / This research presents a theoretical-experimental analysis of column-foundation connection through socket of precast concrete structures, with emphasis in pedestal walls. The experimental program included five models submitted to normal load with large eccentricity, changing the type and the condition of interface: three models had smooth interface and two models had rough interface. In two of smooth models, the bond was eliminated to represent the more appropriate situation of design. Two different configurations of shear keys were used in rough models. Numerical simulations, by finite elements method, were developed on the smooth models without bond, using physical and contact non-linear analyses, and on the rough socket connections, using physical non-linear analyses and perfect adherence of interfaces. The experimental results indicated the need to revalue the principal design methods for this connection. In that way, a design model was proposed for the smooth socket connection, considering friction between the interfaces, and the design of longitudinal walls was suggested as corbels. As it was verified the proximity of rough physical models behavior with a monolithic connection, its vertical reinforcings design was recommended, admitting the total transfer of the efforts. Numerical models had a good convergence and likeness with cracking and tensions field of physical prototypes, in spite of deformations have been smaller than experimental results.

Made available in DSpace on 2014-07-29T15:18:24Z (GMT). No. of bitstreams: 1 2009MELO-CAPITULO1.pdf: 82281 bytes, checksum: 82f866764e23625996fbd50c82fe3c4f (MD5) Previous issue date: 2009-10-22 / In structural system of composite beams with slab and beam, both precast, it is necessary that shear stress is transferred from the slab to the beam through the interface to assure the composite action between beam and slab. This study has the objective of assessing the behavior of composite beams with slab and beam precast connected by pockets. For this, it was developed a computational model based on the Finite Element Method using the commercial software DIANA® 9.3, which make possible the analysis of interaction between shear stresses transferred by interface to precast beam and shear stress on the precast beam due to vertical loading. In the analysis, the behavior of these beams was compared with the behavior of beams with continuous connection, usually employed. In addition, the type of beam-slab interface (with or without shear-key) was analyzed. It is tried from this analysis to confirm some models presented in the literature for design composite beams connected by pockets. Usually, the models used to design of reinforced concrete beams to shear are slightly modified to design the composite beams connected by pockets. The results show that, in fact, there is an increase on the shear stress of precast beam due to a discrete connection provided by pockets / No sistema estrutural de vigas compostas formadas por laje e viga pré-moldadas, para que os elementos estruturais trabalhem efetivamente como um sistema composto, é necessário que as tensões na interface sejam transferidas de um elemento para o outro. Nesta linha, o presente trabalho tem o objetivo de avaliar o comportamento de vigas compostas formadas por viga e laje pré-moldadas ligadas por meio de nichos de concretagem. Para tanto, foi desenvolvido um modelo computacional, com base no Método dos Elementos Finitos, utilizado o programa comercial DIANA® 9.3, com o qual é possível analisar a interação entre as tensões de cisalhamento transferidas da interface para a alma da viga e as tensões de cisalhamento oriundas da força cortante provocada pelo carregamento vertical. Nas análises, são feitas comparações do comportamento dessas vigas com o comportamento de vigas compostas com ligação contínua, usualmente empregada. Também é avaliada a influência do tipo de tratamento da interface (com e sem chave de cisalhamento). Procura-se, assim, confirmar modelos sugeridos pela literatura para o projeto de vigas compostas ligadas mediante nichos existentes, os quais sugerem alterações nos modelos usualmente empregados no projeto de vigas de concreto. A análise dos resultados demonstra que de fato há um aumento nas tensões de compressão na viga pré-moldada devido ao fato da ligação ser discreta

Este trabalho apresenta uma análise teórico-experimental da ligação pilar-fundação por meio de cálice em estruturas de concreto pré-moldado, com ênfase no colarinho. No programa experimental, foram ensaiados cinco protótipos sob força normal com grande excentricidade, variando-se o tipo e condição de interface: três com interface lisa, onde em dois foi eliminada a adesão para representar a situação mais adequada de projeto; e dois com interface rugosa, com duas configurações diferentes de chaves de cisalhamento. Foram realizadas simulações numéricas pelo método dos elementos finitos nos modelos lisos sem adesão, com as não-linearidades físicas e de contato, e nos cálices rugosos, considerando-se a não-linearidade física e a aderência perfeita das interfaces. Os resultados experimentais indicaram a necessidade de se reavaliar os principais métodos de projeto para essa ligação. Desta forma, foi proposto, para o cálice liso, um modelo de projeto considerando o atrito entre as interfaces e o cálculo das paredes longitudinais como consolos. Já para o cálice com interface rugosa, como foi verificada a proximidade do comportamento dos modelos físicos rugosos com uma ligação monolítica, recomendou-se o dimensionamento de suas armaduras verticais, admitindo a transferência total dos esforços, e das armaduras horizontais superiores também com o funcionamento das paredes longitudinais como consolos. Os modelos numéricos apresentaram uma boa convergência e semelhanças na fissuração e no caminho de tensões em relação aos protótipos físicos, apesar das deformações terem sido menores que as observadas experimentalmente. / This research presents a theoretical-experimental analysis of column-foundation connection through socket of precast concrete structures, with emphasis in pedestal walls. The experimental program included five models submitted to normal load with large eccentricity, changing the type and the condition of interface: three models had smooth interface and two models had rough interface. In two of smooth models, the bond was eliminated to represent the more appropriate situation of design. Two different configurations of shear keys were used in rough models. Numerical simulations, by finite elements method, were developed on the smooth models without bond, using physical and contact non-linear analyses, and on the rough socket connections, using physical non-linear analyses and perfect adherence of interfaces. The experimental results indicated the need to revalue the principal design methods for this connection. In that way, a design model was proposed for the smooth socket connection, considering friction between the interfaces, and the design of longitudinal walls was suggested as corbels. As it was verified the proximity of rough physical models behavior with a monolithic connection, its vertical reinforcings design was recommended, admitting the total transfer of the efforts. Numerical models had a good convergence and likeness with cracking and tensions field of physical prototypes, in spite of deformations have been smaller than experimental results.

No description available.

No description available.

No description available.

<p dir="ltr">Reinforced concrete elements are vulnerable to sliding against each other when shear forces are transmitted between them. Shear-friction is the mechanism by which shear is transferred between concrete surfaces. It develops by aggregate interlock between the concrete interfaces while reinforcement crossing the shear interface or normal force due to external loads contributes to the shear resistance. Current design provisions used in the United States (ACI 318-19, AASHTO LRFD (2020), and the PCI Design Handbook (2017)) include design expression for shear-friction capacity. However, the value of the reinforcement yield strength input into the expressions is limited to a maximum of 60 ksi. Furthermore, the concrete strength is not incorporated into the primary design expressions. These limits cause the potential contribution of high-strength reinforcement and high-strength concrete in shear-friction applications from being considered. Therefore, a research program was developed to investigate the possibility of improving current shear-friction design practice and addressing these current limits.</p><p dir="ltr">Specifically, an experimental program was conducted to evaluate the influence of high-strength reinforcement and high-strength concrete on shear-friction strength. In addition, a statistical analysis was performed using a comprehensive shear-frication database comprised of past tests available in the literature. The experimental program consisted of two phases. Phase I included 24 push-off specimens to study the influence of the yield strength of the interface reinforcement (Grade 60 and Grade 100) and the number and size of interface reinforcing bars (6-No.4 and 4-No. 5 bars) with three different interface conditions (rough, smooth, and shear-key). Phase II included 20 push-off specimens with rough interfaces to investigate the influence of the yield strength of the interface reinforcement (Grade 60 and Grade 100) and concrete strength (target strengths of 4000 psi and 8000 psi). The influence of these two variables was observed over a range of reinforcement ratios (ρ = 0.55%, 0.83%, 1.11%, and 1.38%).</p><p dir="ltr">The test results showed that the overall shear-friction strength was the greatest for rough interface specimens, followed by specimens detailed with shear keys. The smooth interface specimens had the lowest strengths. The results of both phases of the experimental program indicated that the use of high-strength reinforcement did not improve shear-friction capacity.</p><p dir="ltr">Furthermore, the results from the Phase II tests showed that increasing the concrete compressive strength led to increased shear-friction capacity. The test results from the experimental program were analyzed and compared with current design provisions, which demonstrated room for improvement of current design practice.</p><p dir="ltr">Following the experimental program, a comprehensive shear-friction database was analyzed, and multilinear regression was used to create a model to predict shear-friction strength. Factors were then applied to the model to provide acceptable design expressions for shear-friction strength (less than 5% unconservative estimates). The database was used to evaluate the factored model and current design provisions.</p><p dir="ltr">The research outcomes, especially the expressions for shear-friction strength that were developed and that include consideration of the concrete compression strength, along with the shear-friction tests demonstrating the lack of strength gain with the use of Grade 100 reinforcement, provide valuable information for the concrete community to help direct efforts toward improving current shear-friction design practice.</p>