Inestabilidad de barras comprimidas de acero y de SMA en elementos de hormigón fabricados con nuevos materiales. Recomendaciones de diseño
[EN] The strain capacity of structures depends on the plastic hinge behaviour. There are different proposals in the scientific literature in order to improve this behaviour in reinforced concrete structures such as the following ones: proposals include the use of fiber reinforced concrete, very high...
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| Tipo de recurso: | tesis doctoral |
| Fecha de publicación: | 2017 |
| País: | España |
| Institución: | Universitat Politècnica de València (UPV) |
| Repositorio: | RiuNet. Repositorio Institucional de la Universitat Politécnica de Valéncia |
| Idioma: | español |
| OAI Identifier: | oai:riunet.upv.es:10251/90650 |
| Acceso en línea: | https://riunet.upv.es/handle/10251/90650 |
| Access Level: | acceso abierto |
| Palabra clave: | Shape Memory Alloys (SMA) Inestabilidad Pandeo Hormigón reforzado con fibras Ultra High Performance Concrete (UHPC) High Performance Concrete (HPC) Fiber Reinforced Concrete (FRC) INGENIERIA DE LA CONSTRUCCION |
| Sumario: | [EN] The strain capacity of structures depends on the plastic hinge behaviour. There are different proposals in the scientific literature in order to improve this behaviour in reinforced concrete structures such as the following ones: proposals include the use of fiber reinforced concrete, very high performance concrete or replacing in the critical structure zone, the steel reinforcement with shape memory alloy and superelasticity bars (from this point forward SMA), among other solutions. However, the strain capacity of hinges is dependent on the compressed reinforcement buckling, which means a drastic diminishing in the bearing capacity and ductility. This phenomenon happens due to the cover spalling or degradation, or due to an insufficient transverse reinforcement arrangement. The design codes propose requirements related to the diameter of longitudinal bars and to the transverse reinforcement separation to assure the bearing capacity or to assure the hinge rotation without the compressed reinforcements buckle. Nevertheless, the aforementioned requirements are not valid in compressed elements made of new materials (fiber reinforced concrete, very high performance concrete or SMA bars). This doctoral thesis analyzes the compressed steel or NiTi - SMA bars behaviour in elements made of conventional, high strength or very high performance concrete, with or without fibres. Therefore, an experimental research has been carried out to study the local instability of the compressed bars (steel and NITI) in concrete elements. 32 columns subject to a bending-compression load have been analyzed. An analytic model has been proposed to analyze the buckling critical stress and length in the compressed bars in concrete elements. This model has been calibrated based on experimental tests. It has been performed an experimental and numerical research to analyze the behaviour of the NITI bars as isolated bars. It has been proposed an analytic model to calculate the relationship stress-strain of the compressed bars that includes the buckling effect. This model has been verified by both experimental and numerical results. Finally, it has been proposed an expression to calculate the maximum separation of the transverse reinforcement according to the required limited stress, for both steel and SMA bars. In order to define that stress, two criteria have been proposed: one of them is based on stresses and the other one on strains. With respect to the concrete without fibres case, the proposed expression has been compared with the current code. |
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