published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / abstract / Civil Engineering / Doctoral / Doctor of Philosophy

No description available.

This study presents an assessment of the seismic performance of rectangular concrete columns internally reinforced with G (Glass) FRP. Eight full-scale columns prototypes, with a shear span of 1650-mm and 350-mm square cross-section, were constructed and tested under simulated seismic waves and constant axial loading. These columns simulate the lower portion of first storey columns between the footing and the contra-flexure point. Therefore, heavy steel-RC footing was post-tensioned to the laboratory strong floor in order to provide rational fixity to the column. The test parameters included reinforcement type, longitudinal reinforcement ratio, level of axial load, and stirrup spacing. Test results showed that deformability of GFRP-RC columns prototypes successfully replaced ductility in steel-RC columns in dissipating the seismic energy in the presence of constant axial load. Furthermore, the failure of sections was prominent by flexure concrete crushing at high drifts. Accordingly, GFRP-RC columns are a doable application in earthquake-resistant structures. / October 2015

Maintaining structural stability is an integral component of building fire safety. Stability must be ensured to provide adequate time for safe egress of the buildings occupants, fire fighting operations and property protection. Structural fire engineering endeavours to design structures to withstand the effects of fire in order to achieve this objective. The behaviour of reinforced concrete in fire is not as well understood as other construction materials, such as steel. This is in part due to the complexity of concrete material behaviour and also due to concrete’s reputation of superior fire performance. Concrete technology is, however, continually evolving; structures are increasingly slender, more highly stressed and have higher compressive strengths. A more robust understanding of concrete’s behaviour in fire will enable predictions of the implications of changing concrete technology and also help to properly quantify the fire safety risk associated with concrete structures. A fundamental key to understanding structural fire performance is the relationship between the thermal environment induced by the fire and the structure. Significant thermal variation has been found experimentally to exist within fire compartments. Despite this the design of structures for fire almost universally assumes the compartment thermal environment to be homogeneous. In this thesis the implications of compartment fire non-uniformity for concrete structural behaviour is investigated to assess the validity of the uniform compartment temperature assumption. The investigation is conducted using numerical tools; a detailed review of the necessary background knowledge, material modelling of reinforced concrete, finite element modelling of reinforced concrete structures and compartment fire thermal variation is included. The behaviour of a two-way spanning reinforced concrete slab is used as a structural benchmark. The membrane behaviour exhibited by two-way spanning RC slabs at high temperatures has been previously studied under uniform thermal conditions. They therefore are an ideal benchmark for identifying the influence of non-uniform thermal environments for behaviour. The relationship between gas phase temperature variation and concrete thermal expansion behaviour, which is fundamental to understanding concrete high temperature structural behaviour, is first investigated. These preliminary studies provide the necessary fundamental understanding to identify the influence of gas phase temperature variation upon the membrane behaviour of reinforced concrete slabs. The individual influences of spatial and temporal variation upon slab membrane behaviour are investigated and the behaviour under non-uniform thermal variation contrasted with uniform thermal exposure behaviour. The influence of spatial variation of temperature is found to be strongly dependent upon the structural slenderness ratio. The tensile membrane action of slender slabs is particularly susceptible to the distorted slab deflection profiles induced by spatial variation of gas temperature. Conversely the compressive membrane behaviour of stocky slabs is found to be insensitive to the deformation effects induced by spatial variation of temperature. The influence upon slender slabs is demonstrated under a range of temporal variations indicating that the thermal response of concrete is sufficiently fast to be sensitive to realistically varying distributions of temperature. Contrasting behaviour induced by uniform and non-uniform thermal exposures indicates that uniform temperature assumptions provide both conservative and unconservative predictions of behaviour. The accuracy of the uniform temperature assumptions was also found to be dependent upon the type of fire, for example, fast hot and short cool fires. Additionally, the sensitivity of structural performance to deformations caused by spatial variation of temperature demonstrated in this thesis challenges the purely strength based focus of traditional structural fire engineering. Spalling is an important feature of concrete’s high temperature behaviour which is not currently explicitly addressed in design. The incorporation of spalling into structural analysis is not, however, straightforward. The influence of spalling upon behaviour has therefore been dealt with separately. A spalling design framework is developed to incorporate the effects of spalling into a structural analysis. Application of the framework to case studies demonstrates the potential for spalling to critically undermine the structural performance of concrete in fire. It also demonstrates how the framework can be used to quantify the effects of spalling and therefore account for these in the structural fire design addressing spalling risk in a rational manner.

Blocos sobre estacas ou blocos de coroamento são elementos estruturais usados para transferir as ações da superestrutura para um conjunto de estacas. São encontrados em infra-estruturas de pontes e edifícios. O conhecimento de seu real comportamento estrutural é de fundamental importância, pois são elementos estruturais que garantem a segurança de toda a estrutura. Ainda não há consenso no meio técnico quanto ao seu real comportamento estrutural; também não se sabe a real forma geométrica das bielas de compressão no Estado Limite Último para a aplicação do método biela-tirante, e falta normalização deste elemento estrutural; estes são alguns aspectos que tornam este trabalho necessário. Com o objetivo de contribuir para diretrizes de projeto, foram apresentados os critérios utilizados nos projetos de blocos sobre estacas e desenvolvido, por meio de resultados de modelos analíticos, um método para a verificação da tensão de compressão na biela junto ao pilar. Nos modelos adotados variaram-se os diâmetros de estacas e dimensões de pilar. Conclui-se que os resultados são de grande relevância, pois os resultados obtidos mostraram-se muito coerentes por serem constantes em função da quantidade de estacas e da relação x/d. / Piles caps are structural elements used to transfer actions of the superstructure to a group of piles. They are found in infrastructures of bridges and buildings. The knowledge of its real structural behavior presents fundamental importance, once piles caps are structural elements that guarantee the safety of all structure. There is no consensus yet between specialists on its real structural behavior, the real geometric shape of the struts on the ULS for the application of the strut-and-tie model its not know, and the lack of standardization of this structural element are some of the aspects that makes this work necessary. With the objective to contribute to the design guidelines, were presented the criteria used in projects of piles caps and developed through results of analytical models, a method for checking the compressive stress at the strut near the column. Piles diameters and column dimensions of the models were been varied. It was concluded that the results are of great relevance, because the values obtained proved to be very consistent since they are in depending on the amount of piles and the relationship x/d.

Neste trabalho são apresentados procedimentos para o dimensionamento de elementos de chapa de concreto armado com armaduras em malha ortogonal, com as direções não coincidentes com as das tensões principais. É feita uma revisão dos conceitos teóricos do Método de Baumann e do Modified Compression Field Theory, sendo que no primeiro foi incorporada a relação tensão-deformação do concreto fissurado proposta por Vecchio e Collins. Para a análise das deformações principais é feita uma revisão do estado duplo de deformações utilizando-se o círculo de Mohr. Posteriormente são feitas comparações entre os resultados de modelo físicos e as formulações analíticas, bem como entre os resultados de modelos hipotéticos utilizando ambos os métodos, com o objetivo de valorizar o Método de Baumann dada a sua simplicidade, mostrando que este apresenta resultados a favor da segurança. Buscou-se através do Método de Baumann avaliar os benefícios da utilização de armaduras de compressão. / Procedures are presented for the reinforced concrete membranes design with orthogonal mesh, which does not coincide with principal stress directions. A review of the theoretical fundamentals for Baumann Method and Modified Compression Field Theory is presented, and in the first was used the stress-strain relationships for the cracked concrete developed by Vecchio and Collins. A review of the plane strain is presented using the Mohr Circle for the principal strains analysis. Later, the results of tested panels and the theoretical formulations are compared, also between hypothetical panels using both methods, to enhance the Baumann Method due its simplicity, ensuring that presents overestimated results. Benefits were evaluated through Baumann Method using compression reinforcement.

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