UHPC (ultra-high performance concrete) is a relatively new type of concrete that exhibits mechanical properties that are far superior to those of conventional concrete and in some cases rival those of steel. The main characteristics that distinguish UHPC from conventional reinforced concrete are the improved compressive strength, the tensile strength, the addition of steel fibers, and the resistance to corrosion and degradation. The mechanical properties of UHPC allow for smaller, thinner, lighter sections to be designed while strength is maintained or improved. The use of UHPC has been limited to a few structural applications due to the high cost of the materials and the lack of established design guidelines. A proposed material model based on material and finite element models has served as the foundation of this research effort. The model was used to minimize the dimension of an optimum section in order to limit the material usage and maximize the performance. In the model, the top flange served as the riding surface and contained no reinforcing steel to resist shear. The lack of steel reinforcement allowed for the possibility of a punching shear failure to occur from the application of a point load such as a wheel tire patch load. The model and optimized section served as the foundation for this research, the characterization of punching shear capacity of thin UHPC plates. A total of 12 UHPC slabs were tested to failure to determine the boundary between a flexural failure and a punching shear failure. The variables considered were the slab thickness and loading plate dimensions. The results of the testing were compared to existing models for punching shears and other failure modes, with varying success. The test results aided in the development of a design equation for the prediction of punching shear in UHPC slabs. After evaluation of the test results, recommendations are made as to which model predicts the punching shear capacity of UHPC slabs and the minimum slab thickness required to prevent a punching shear failure. / Master of Science

Over the life span of a structure it may become necessary to retrofit, or strengthen certain components or elements. This may be due to construction errors, changes in use and occupancy, or changes due to material deterioration or damage. Slab-column connections in flat slab structures might need to be strengthened for punching shear. Using steel shear bolts to strengthen connections for punching shear is a new technique used for retrofit that was developed at the University of Waterloo. If the retrofitted part of the structure is exposed to the atmosphere, or to chemicals such as deicing salts, the steel can corrode, thus furthering to damage the structure. Non-corrosive materials that can replace the steel shear bolts can be a good practical alternative to steel. Reported in this thesis are the results of research on the development and use of non-corrosive shear bolts for reinforced concrete interior slab-column connections. Externally applied shear reinforcing bolts provide the punching shear reinforcement strength, while allowing the flexibility and ease of installation of an external application after construction. By providing a bearing area against both sides of the slab surface, the formation of punching shear cracks can be restrained, and the connection can become strengthened against punching shear failure. Three different types of non-corrosive shear bolts were developed and tested. The first was an off-the-shelf glass fiber reinforced polymer (GFRP) bolt / nut product. The two others used two different GFRP core rods with aluminum fittings crimped to their ends. A total of six specimens were tested, four were tested under an increasing static load, while two were tested with an unbalanced pseudo-dynamic lateral load. All six specimens were designed to fail in punching shear before reaching their flexural capacity. The results are compared against previous test results of specimens both unreinforced and reinforced with steel shear bolts to determine their effectiveness. From the test results it was found that the GFRP shear bolts did strengthen the connections for punching shear. The GFRP nut and bolt did not strengthen the connection, and, in fact, decreased its overall strength when compared to the unreinforced specimen. The presence of the GFRP shear bolts also increased the connection ductility and the deflection capability. In the pseudo-dynamic tests the GFRP shear bolts significantly increased the amount of energy dissipated by the connection under reverse cyclic loading. The results of the testing appeared to be depended on the proper application of the crimping technique to place the bolts in the slab.

Over the life span of a structure it may become necessary to retrofit, or strengthen certain components or elements. This may be due to construction errors, changes in use and occupancy, or changes due to material deterioration or damage. Slab-column connections in flat slab structures might need to be strengthened for punching shear. Using steel shear bolts to strengthen connections for punching shear is a new technique used for retrofit that was developed at the University of Waterloo. If the retrofitted part of the structure is exposed to the atmosphere, or to chemicals such as deicing salts, the steel can corrode, thus furthering to damage the structure. Non-corrosive materials that can replace the steel shear bolts can be a good practical alternative to steel. Reported in this thesis are the results of research on the development and use of non-corrosive shear bolts for reinforced concrete interior slab-column connections. Externally applied shear reinforcing bolts provide the punching shear reinforcement strength, while allowing the flexibility and ease of installation of an external application after construction. By providing a bearing area against both sides of the slab surface, the formation of punching shear cracks can be restrained, and the connection can become strengthened against punching shear failure. Three different types of non-corrosive shear bolts were developed and tested. The first was an off-the-shelf glass fiber reinforced polymer (GFRP) bolt / nut product. The two others used two different GFRP core rods with aluminum fittings crimped to their ends. A total of six specimens were tested, four were tested under an increasing static load, while two were tested with an unbalanced pseudo-dynamic lateral load. All six specimens were designed to fail in punching shear before reaching their flexural capacity. The results are compared against previous test results of specimens both unreinforced and reinforced with steel shear bolts to determine their effectiveness. From the test results it was found that the GFRP shear bolts did strengthen the connections for punching shear. The GFRP nut and bolt did not strengthen the connection, and, in fact, decreased its overall strength when compared to the unreinforced specimen. The presence of the GFRP shear bolts also increased the connection ductility and the deflection capability. In the pseudo-dynamic tests the GFRP shear bolts significantly increased the amount of energy dissipated by the connection under reverse cyclic loading. The results of the testing appeared to be depended on the proper application of the crimping technique to place the bolts in the slab.

This thesis examines punching shear response of reinforced-concrete flat slabs under fire conditions. The shear behaviour of concrete in fire is relatively poorly understood compared to its flexural response. Failures such as the Gretzenbach car park failure in Switzerland (2004) have prompted concerns over the punching shear capacity of flat slabs in fire. The shear behaviour of reinforced-concrete in fire depends on degradation of the individual material properties with temperature, their interaction, and more recently recognised, the effects of restrained thermal expansion. Through experimental testing this thesis aims to build a foundation understanding of the punching shear behaviour of flat reinforced-concrete slabs in fire conditions. A series of shear blocks, tested after exposure to elevated temperature (realistic fire temperature), were used to develop an understanding of the effects of elevated temperature on the shear transfer performance of reinforced-concrete. These tests allowed the complex interplay of shear-carrying mechanisms at ambient temperature to be extended to the case of post-elevated temperature. Fifteen slab-column punching shear specimens were tested under both applied load and extreme heating. In particular, the effects of restrained thermal expansion were experimentally investigated by altering the support conditions of the slab-column specimens. A purpose-built restraint frame allowed the boundary support conditions to be either fully restrained or unrestrained. This experimental series is the only series to have tested restrained specimens at elevated temperatures, though previous researchers have simulated the thermal restraint effects and reported the importance of restrained thermal expansion and curvature on the behaviour of punching shear. Parameters of slab thickness and reinforcement ratio were also varied to investigate their respective impacts on punching shear behaviour at elevated temperature. The thicker 100 mm reinforced slabs failed in punching shear, whereas the 50 mm and 75 mm thick slabs failed in flexure-shear mechanisms and the unreinforced slabs failed in flexure. Clear behavioural differences were observed between specimens with different support conditions. Unrestrained 100 mm thick slabs under sustained load failed soon after heating began, whereas none of the corresponding restrained specimens failed during heating. One restrained, heavily reinforced specimen failed during cooling, whilst under sustained load. This is the first recorded punching shear failure during the cooling phase of an elevated temperature test and may also be the first recorded test specimen ever to have failed during the cooling phase of an elevated temperature test. This failure highlights the unknown and potentially unsafe behaviour of structures during the cooling phase. Further structural investigation of the cooling behaviour of concrete flat slabs after exposure to fire, needs to be undertaken. Most of the specimens’ central deflection was away from the heat source (in the direction of loading) during the whole test, irrespective of support condition. The test setup was assessed to investigate the unusual slab-column deflection away from the heat source, however the complex behaviour observed during the tests cannot currently be explained. It is assumed that the degradation in concrete properties and non-linear material behaviour dominates over the thermal expansion of the slabs. Quantitative and qualitative comparisons are presented, though the quantitative data is impacted by size effect, non-repeatable heating application between tests and jack friction influences on specimens with low capacities. Eurocode 2 punching shear prescriptive elevated temperature design, extends the ambient temperature equation for elevated temperature use, by degrading the temperature-dependant parameters by factors. Support conditions are not considered, with the code specifically telling the designer not to consider in-plane thermal expansion effects, therefore consequently ignoring the premature punching shear failure that can occur. Furthermore, the ambient temperature equation is based on the regression of available experimental data at the time and does not consider the reinforcement as a shear transfer mechanism. The experimental capacities of the 100 mm thick, reinforced slabs that failed in pure punching shear mechanism were similar to the Eurocode 2 punching shear prescriptive design capacity, when directly compared. The unrestrained support condition was shown to be consistently, not conservatively predicted by Eurocode 2, whereas the restrained support condition capacities were conservatively predicted. It is comforting to know that the Eurocode 2 design predicts the restrained supported slabs conservatively, as real buildings are more likely to have supports closer to the restrained condition rather than the unrestrained support condition. A sensitivity analysis of the Eurocode 2 prescriptive design equation shows it is highly sensitive to the concrete strength degradation and not the variable, cp, which was used to make a support condition comparison in this thesis. This indicates how the Eurocode 2 equation for punching shear capacity lacks in its consideration of whole structural behaviour. The Critical Shear Crack Theory has been proposed as the background to a harmonised shear design approach, called Model Code 2010. The Critical Shear Crack Theory was safe in predicting the experimental punching shear capacities. There were large variances for the 100 mm thick slabs, however they are consistent with the original model comparison to test data. An expansion of the Critical Shear Crack Theory for elevated temperature requires further validation with experimental restrained thermal expansion tests, such as those presented in this thesis. Finally, a digital image correlation technique has been proven to be a reliable method to measure structural displacements of concrete at elevated temperatures. Digital image correlation allowed the crack locations and slab rotation angles to be visualized throughout testing. No other measurement techniques are able to provide similar versatility in fire testing such as that presented herein.

Atualmente, alguns códigos como o CEB/90 e o texto base da NB-1/94 (ainda em fase de apreciação pelo meio técnico) têm apresentado inovações com relação à verificação da resistência à punção. Fez-se então, neste trabalho, uma análise do texto base da NB-1/94 referente à punção, comparando suas recomendações com algumas das fornecidas pelo CEB/90. Observou-se uma certa divergência entre os dois códigos com relação a pilares de borda e de canto, fornecendo o CEB/90 um tratamento mais simplificado para essas duas situações. Além disso, observa-se que, ao contrário do CEB/90, o texto base não menciona as seguintes recomendações: utilização de uma armadura a ser disposta ao longo das bordas livres da laje, destinada a combater esforços de torção, e limitação da resistência do concreto em 50 MPa para essas verificações. Observou-se, ainda, uma omissão desses dois códigos com relação à situação de pilares internos submetidos a momentos fletores atuando em duas direções diferentes. Sugere-se, ainda, ao texto base, a inclusão de expressões que visem a facilitar e agilizar a sua aplicação. Após essa análise, foram apresentados exemplos de cálculo para pilares internos, de borda e de canto, tanto com como sem armadura de punção, verificados segundo as recomendações do texto base da NB-1/94, do EUROCODE N.2, do CEB/90 e do ACI 318/89. Por fim, comparam-se resultados experimentais com valores dados por estes códigos, visando determinar suas respectivas eficiências frente a alguns parâmetros, tais como, por exemplo, a presença de armadura transversal ou a relação entre os lados do pilar. Verifica-se que a utilização de armaduras de combate à punção pode elevar substancialmente o valor da resistência da ligação, além de torná-la mais dúctil. As observações referentes à comparação entre os valores fornecidos através de ensaios e os dados pelos códigos devem ser levadas em consideração apenas como uma indicação de seus respectivos comportamentos, necessitando-se de mais dados para uma afirmação mais conclusiva. / Nowadays, some standards like CEB/90 and the Brazilian code basic text NB-1/94 (not approved yet) have presented some innovations for the punching shear strength. In this work, a comparative analysis is presented about the NB1-94 basic text recommendations and some presented by the CEB/90. Some differences are noted between the NB1-94 basic text and the CEB/90 recommendations relatives to corner and edge columns. The CEB/90 has a simplified treatment for these situations. lt is noted that, in opposition to the CEB/90, the NB1-94 basic text about punching shear strength does not mention an additional reinforcement to be placed at the free edges of the slab, to provide torsion strength, and neither have a limit value of 50 MPa for the concrete compressive strength. lt is also noted that the CEB/90 and the NB1-94 basic text do not have a recommendation for internal columns with bending moments acting on two different directions. lt is suggested that the NB1-94 basic text includes some expressions that can make its application easier and faster. After this analysis, some examples are presented with internal, edge and corner columns, with and without shear reinforcement, verified by the NB1-94 basic text, the EUROCODE N.2, the CEB/90 and the ACI 318/89 recommendations. Finally, a comparative analysis between some experimental results and those given by the codes is presented. The experimental results were related to some parameters like, for instance, the presence of shear reinforcement or the column sides ratio. lt is verified that the shear reinforcement utilization can give more resistance and ductility to the connection. Finally, it is noted that the observations about the comparison between the experimental results and the values given by the codes can just be taken like a behavior indication for the connections. For conclusive affirmations, more experimental analysis are necessary.

Atualmente, alguns códigos como o CEB/90 e o texto base da NB-1/94 (ainda em fase de apreciação pelo meio técnico) têm apresentado inovações com relação à verificação da resistência à punção. Fez-se então, neste trabalho, uma análise do texto base da NB-1/94 referente à punção, comparando suas recomendações com algumas das fornecidas pelo CEB/90. Observou-se uma certa divergência entre os dois códigos com relação a pilares de borda e de canto, fornecendo o CEB/90 um tratamento mais simplificado para essas duas situações. Além disso, observa-se que, ao contrário do CEB/90, o texto base não menciona as seguintes recomendações: utilização de uma armadura a ser disposta ao longo das bordas livres da laje, destinada a combater esforços de torção, e limitação da resistência do concreto em 50 MPa para essas verificações. Observou-se, ainda, uma omissão desses dois códigos com relação à situação de pilares internos submetidos a momentos fletores atuando em duas direções diferentes. Sugere-se, ainda, ao texto base, a inclusão de expressões que visem a facilitar e agilizar a sua aplicação. Após essa análise, foram apresentados exemplos de cálculo para pilares internos, de borda e de canto, tanto com como sem armadura de punção, verificados segundo as recomendações do texto base da NB-1/94, do EUROCODE N.2, do CEB/90 e do ACI 318/89. Por fim, comparam-se resultados experimentais com valores dados por estes códigos, visando determinar suas respectivas eficiências frente a alguns parâmetros, tais como, por exemplo, a presença de armadura transversal ou a relação entre os lados do pilar. Verifica-se que a utilização de armaduras de combate à punção pode elevar substancialmente o valor da resistência da ligação, além de torná-la mais dúctil. As observações referentes à comparação entre os valores fornecidos através de ensaios e os dados pelos códigos devem ser levadas em consideração apenas como uma indicação de seus respectivos comportamentos, necessitando-se de mais dados para uma afirmação mais conclusiva. / Nowadays, some standards like CEB/90 and the Brazilian code basic text NB-1/94 (not approved yet) have presented some innovations for the punching shear strength. In this work, a comparative analysis is presented about the NB1-94 basic text recommendations and some presented by the CEB/90. Some differences are noted between the NB1-94 basic text and the CEB/90 recommendations relatives to corner and edge columns. The CEB/90 has a simplified treatment for these situations. lt is noted that, in opposition to the CEB/90, the NB1-94 basic text about punching shear strength does not mention an additional reinforcement to be placed at the free edges of the slab, to provide torsion strength, and neither have a limit value of 50 MPa for the concrete compressive strength. lt is also noted that the CEB/90 and the NB1-94 basic text do not have a recommendation for internal columns with bending moments acting on two different directions. lt is suggested that the NB1-94 basic text includes some expressions that can make its application easier and faster. After this analysis, some examples are presented with internal, edge and corner columns, with and without shear reinforcement, verified by the NB1-94 basic text, the EUROCODE N.2, the CEB/90 and the ACI 318/89 recommendations. Finally, a comparative analysis between some experimental results and those given by the codes is presented. The experimental results were related to some parameters like, for instance, the presence of shear reinforcement or the column sides ratio. lt is verified that the shear reinforcement utilization can give more resistance and ductility to the connection. Finally, it is noted that the observations about the comparison between the experimental results and the values given by the codes can just be taken like a behavior indication for the connections. For conclusive affirmations, more experimental analysis are necessary.

As lajes lisas podem oferecer diversas vantagens quando comparadas ao sistema de lajes, vigas e pilares, sendo, em muitos casos, mais econômicas. O uso da protensão pode oferecer outras vantagens, tais como um melhor controle da fissuração e dos deslocamentos transversais da laje. Como a punção é um dos pontos fracos das lajes lisas protendidas, face à grande esbeltez destas lajes, apresentam-se resultados experimentais de ligações laje-pilar interno, com carregamento concêntrico, com e sem armadura de punção (conectores tipo-pino), com e sem protensão por pós-tração (cabos não aderentes). Os principais aspectos analisados foram as influências da armadura de punção e da protensão na resistência da ligação laje-pilar. Fez-se também uma análise envolvendo a previsão da resistência da ligação, dada por algumas normas e códigos. Observa-se que, de um modo aproximado, a armadura de punção eleva significativamente a resistência do modelo à punção, seja ele de concreto armado ou protendido. Observa-se ainda que, embora diminuindo a taxa de armadura dos modelos de concreto armado, para que se introduzissem as cordoalhas de protensão, os valores experimentais obtidos mostram que a presença da protensão aumentou a resistência da ligação. De um modo geral, a melhor norma que reflete o comportamento da ligação lajepilar é a Revisão da NB-1 (2000). Com relação aos modelos protendidos, o ACI poderia ter tido um bom desempenho, caso não houvesse uma restrição tão rígida com relação ao uso de armaduras de punção / The use of flat plates may offer some economical and aesthetic benefits when compared with other structural systems. The use of post-tensioned slabs may offer other advantages, as a better crack and deflection control and a thinner slab for the same span and load conditions. This work presents some experimental results and conclusions about the punching shear failure, as it is a critical problem for flat plate structures, post-tensioned or not. The main aspects analyzed are the influence of the shear reinforcement (studs) and of the post-tensioning with unbonded tendons on a slab – internal column connection strength. A comparison between experimental results and those given by some standards is presented. This comparison aims to verify if the codes accurately predict the punching shear strength of the connection. It can be noted that, in an specific comparison, the studs enhance the punching shear strength of the slab-column connection. In spite of the use of less flexural reinforcement in the post-tensioned models, the punching shear strength of the connection had a higher value when compared with the reinforced ones. This fact is due to the presence of the prestressed strands

O crescente uso de lajes sem vigas (lisa com ou sem capitel) como solução estrutural de edificações, justificado por questões econômicas e construtivas, têm destacado a importância do estudo desses elementos estruturais. Já as desvantagens desse sistema estrutural estão associadas às altas tensões geradas na região próxima dos pilares, originando o fenômeno de punção. As normas atuais especificam uma seção íntegra resistente para dimensionamento à punção, entretanto, devido principalmente à passagem de instalações hidráulicas e elétricas através dos pavimentos, é necessária a execução de furações, em alguns casos muito próximas ao contorno dos pilares, o que implica diretamente na redução dessa seção e da resistência das lajes. Portanto, são necessários modelos de cálculo específicos para isso. A NBR 6118 tem critérios para esse problema, mas são antigos e precisam ser modernizados. Assim, comparando os dados experimentais de algumas pesquisas com as cargas últimas estimadas para normas vigentes (fib MC2010:2013, EC2:2004, ACI-318:2014 e NBR 6118:2014), este trabalho teve como objetivo identificar limitações das normas estudadas e verificar a eventual possibilidade de melhorias. Com base nos resultados observados foi proposta uma alteração para a NBR 6118: 2014 no cálculo da punção para lajes lisas com furo(s) na região do pilar, de modo que seja considerado no dimensionamento o momento gerado pela excentricidade do perímetro crítico devido à presença de furo(s) na laje. / The increasing use of flat slabs (slabs without beams with or without drop panel) as a structural solution of buildings, justified by economic and constructive issues, has highlighted the importance of the study of these structural elements. The disadvantages of this structural system are associated with high stresses generated in the region near of the columns, causing the punching shear phenomenon. The current standards specify a resistant section for punching shear design, however, due mainly to the passage of hydraulic and electric installations through the floors, it is necessary to execute holes, in some cases very close to the boundaries of the columns, which reduces this section and the slab strength. Therefore, it is necessary to specify calculation models for that. The NBR 6118 has criteria for this problem, nonetheless it is old and needs to be modernized. Comparing experimental data from some researches, with the estimated ultimate loads for current standards (fib MC2010: 2013, EC2: 2004, ACI-318: 2014 and NBR 6118: 2014), this work had as objective to identify limitations of the standards studied and verify possible improvements. Based on the observed results, it was proposed a modification for NBR 6118: 2014 in the design of the punching shear of flat slabs with hole(s) near of the column, considering the moment caused by the eccentricity of the critical perimeter due to the presence of hole(s) in the slab.

Flat plate systems are constructed with slabs directly supported on columns. Since there are no beams in the system, the behavior of connections between the slabs and columns play a crucial role. Due to the sudden and brittle nature of punching shear failures, slab-column connection design must be conducted with proper safety precautions. The first part of this study aims to evaluate the safety level of different design expressions in the codes. Fir this purpose, the ability of ACI 318-11, TS-500 and Eurocode-2 to estimate punching shear strength was examined in light of experimental results compiled from previous research. Interior and exterior connections were examined in the course of the study. In the second part of the study, beam and shell models were calibrated to simulate the load-deformation response of interior slab-column connections in light of experimental results. In the final part of this thesis, a typical floor plan of a flat plate system was analyzed to investigate the possibility of a progressivefailure mechanism after punching failure takes place at a slab-column connection. Minimum post-punching capacity required to avoid progressive punching failure in a floor was estimated. It is believed that, the results of this study can be helpful in guiding engineers in understanding the safety inherent in punching shear design expressions and to take necessary precautions against progressive collapse.

Reinforced concrete slab-column structures are widely used because of their practicality. However, this type of structures can be subject to punching-shear failure in the slab-column connections. Without shear reinforcement, the slab-column connection can undergo brittle punching failure, especially when the structure is subject to lateral loading in seismic zones. The shear bolts are a new type of transverse reinforcement developed for retrofit of existing structures against punching. This research focuses on how the shear bolts can improve the punching-shear capacity and ductility of the existing slab-column connections under vertical service and lateral seismic loads. A set of nine full-scale reinforced concrete slab-column connection specimens were tested under vertical service and cyclic loads. The vertical (gravity) load for each specimen was kept at a constant value throughout the testing. The cyclic lateral drift with increasing intensity was applied to the columns. The specimens were different in number of bolts, concrete strength, number of openings, and level of gravity punching load. Strains in flexural rebars in the slabs, crack widths, lateral loads, and displacements were obtained. The peak lateral load (moment) and its corresponding drift ratio, connection stiffness, crack width, and ductility were compared among different specimens. The testing results show that shear bolts can increase lateral peak load resisting capacity, lateral drift capacity at peak load, and ductility of the slab-column connections. Shear bolts also change the failure mode of the slab-column connections and increase the energy dissipation capacity. The thesis includes also research on the development of guidelines for shear bolt design for concrete slab retrofitting, including the punching shear design method of concrete slab (with shear bolts), dimensions of bolts, spacing, and influence of bolt layout patterns. Suggestions are given for construction of retrofitting method using shear bolts. Recommendations are also presented for future research.