Publicação
High performance fiber reinforced concrete for the replacement of shear stirrups
| Resumo: | Corrosion of steel reinforcements, especially stirrups, is considered as one of the most common reasons that shorten the service life of the reinforced concrete, RC, structures. In several cases the rehabilitation of corroded RC structures is so expensive and time consuming that a decision for the demolishment of such members is currently taken, by bringing the consequent economic, social and environmental adverse impacts. Hence, in recent years there is an increasing demand for enhancing the durability and sustainability of concrete structures. The main purpose of the present thesis is to introduce a new design framework for constructing highly durable and structurally effective prefabricated concrete beams without stirrups. These elements are produced by means of a tailor-made high performance fiber reinforced concrete (HPFRC), which is capable of suppressing the steel stirrups without occurring shear failure. A hybrid flexural reinforcement system is used for these beams, composed of glass fiber reinforced polymer (GFRP) rebars placed near to the outer surface of the tensile zone and steel reinforcements positioned with higher HPFRC cover to be protected against the corrosion, which is considered another strategy for enhancing the durability, ensuring the required ductility, and attending fire issues in terms of safety at ultimate limit states. This research combines experimental, numerical and analytical approaches to evaluate the possibilities of the proposed strategy for developing pre-fabrication beams of material and structural requisites at competitive costs. The HPFRC is developed in order to have self-compacting requisites and properties at fresh stage suitable for the type of structural application to be developed, taking also into consideration the influence of fiber distribution and orientation. The mechanical properties of this HPFRC at harden stage are deeply characterized, mainly the postcracking behavior, due to the influence of fiber reinforcement in the fracture parameters of this cementitious material. Considering the influence of shear span to effective depth ratio, / a d, on shear behavior of the beams, the response of both HPFRC short span (1 / 2.5 a d ) and slender beams ( / 2.5 a d ) is evaluated under shear loading configuration. During these studies, the effectiveness of fiber dosage and prestress level applied to GFRP and/or steel flexural reinforcements to improve the shear capacity and failure mode of the designed beams is evaluated as well. By considering the obtained experimental results, the predictive performance of some analytical formulations for the shear resistance of fiber reinforced concrete beams is assessed. An analytical and a FEM-based numerical approach capable of capturing the relevant nonlinear phenomena of the intervening materials in this type of RC members are adopted to demonstrate the benefits of fiber reinforcement and prestress level on the load carrying capacity at serviceability limit state conditions and at steel yield initiation. Based on the developed research, it is demonstrated the possibility of combining HPFRC and FRP reinforcement systems for developing innovative construction systems of high structural performance and ductility, immunes to corrosion phenomena, capable of constituting a new generation of durable and cost competitive solutions for a more sustainable built environment. |
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| Autores principais: | Soltanzadeh, Fatemeh |
| Assunto: | Durability Beams without stirrups Shear resistance High performance fiber reinforced concrete Prestress FEM analysis Durabilidade Vigas sem estribos Resistência ao corte Betão de elevado desempenho reforçado com fibras Pré-esforço Análise pelo método dos elementos finitos |
| Ano: | 2016 |
| País: | Portugal |
| Tipo de documento: | tese de doutoramento |
| Tipo de acesso: | acesso aberto |
| Instituição associada: | Universidade do Minho |
| Idioma: | inglês |
| Origem: | RepositóriUM - Universidade do Minho |
| Resumo: | Corrosion of steel reinforcements, especially stirrups, is considered as one of the most common reasons that shorten the service life of the reinforced concrete, RC, structures. In several cases the rehabilitation of corroded RC structures is so expensive and time consuming that a decision for the demolishment of such members is currently taken, by bringing the consequent economic, social and environmental adverse impacts. Hence, in recent years there is an increasing demand for enhancing the durability and sustainability of concrete structures. The main purpose of the present thesis is to introduce a new design framework for constructing highly durable and structurally effective prefabricated concrete beams without stirrups. These elements are produced by means of a tailor-made high performance fiber reinforced concrete (HPFRC), which is capable of suppressing the steel stirrups without occurring shear failure. A hybrid flexural reinforcement system is used for these beams, composed of glass fiber reinforced polymer (GFRP) rebars placed near to the outer surface of the tensile zone and steel reinforcements positioned with higher HPFRC cover to be protected against the corrosion, which is considered another strategy for enhancing the durability, ensuring the required ductility, and attending fire issues in terms of safety at ultimate limit states. This research combines experimental, numerical and analytical approaches to evaluate the possibilities of the proposed strategy for developing pre-fabrication beams of material and structural requisites at competitive costs. The HPFRC is developed in order to have self-compacting requisites and properties at fresh stage suitable for the type of structural application to be developed, taking also into consideration the influence of fiber distribution and orientation. The mechanical properties of this HPFRC at harden stage are deeply characterized, mainly the postcracking behavior, due to the influence of fiber reinforcement in the fracture parameters of this cementitious material. Considering the influence of shear span to effective depth ratio, / a d, on shear behavior of the beams, the response of both HPFRC short span (1 / 2.5 a d ) and slender beams ( / 2.5 a d ) is evaluated under shear loading configuration. During these studies, the effectiveness of fiber dosage and prestress level applied to GFRP and/or steel flexural reinforcements to improve the shear capacity and failure mode of the designed beams is evaluated as well. By considering the obtained experimental results, the predictive performance of some analytical formulations for the shear resistance of fiber reinforced concrete beams is assessed. An analytical and a FEM-based numerical approach capable of capturing the relevant nonlinear phenomena of the intervening materials in this type of RC members are adopted to demonstrate the benefits of fiber reinforcement and prestress level on the load carrying capacity at serviceability limit state conditions and at steel yield initiation. Based on the developed research, it is demonstrated the possibility of combining HPFRC and FRP reinforcement systems for developing innovative construction systems of high structural performance and ductility, immunes to corrosion phenomena, capable of constituting a new generation of durable and cost competitive solutions for a more sustainable built environment. |
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