Upgrading the push-off test to analyze the contribution of steel fiber on shear transfer mechanisms
- Autores: Javier Andrés Echegaray Oviedo
- Directores de la Tesis: Juan Navarro Gregori (dir. tes.), Pedro Serna Ros (dir. tes.)
- Lectura: En la Universitat Politècnica de València ( España ) en 2014
- Idioma: inglés
- Tribunal Calificador de la Tesis: Pedro Miguel Sosa (presid.), Antoni Cladera Bohigas (secret.), Antonio R. Marí Bernat (voc.)
- Materias:
- Enlaces
- Tesis en acceso abierto en: RiuNet
- Resumen
The shear behavior of a specimen made of reinforced concrete is complex. Resisting mechanisms are affected by different factors, such as section form, specimen slimness, longitudinal and transversal reinforcement arrangement, bond between concrete and steel, among others. The addition of steel fibers to concrete improves both ductility and tensile behavior to provide good control during the cracking process. Fibers also enhance the shear behavior of structural elements by increasing ultimate resistance and ductility. Push-off tests have been used to study shear transfer mechanisms in concrete. Indeed, the shear strength of the specimen depends on the contribution of both concrete and shear reinforcement. Aggregate interlock (framed within the Crack Shear Friction Theory) signifficantly contribute to the concrete shear capacity. In the last few decades, new kinds of concrete have been developed for industrial use, such as high strength concrete (HSC), self-compacting concrete (SCC) or fiber reinforced concrete (FRC), among others. In these new materials, the aggregate interlock phenomenon may differ when compared to conventional concrete (CC). Information about shear transfer mechanisms in fiber reinforced concrete elements is lacking in the literature. Self-compacting concrete (SCC) is that which, as a given studied mixing proportion and through the utilization of superplasticizer additives, compacts under its own weight without the need for vibrational energy or the use of any other compacting method. It presents no sign of segregation, coarse aggregate blocking, bleeding or cement grout exudation. The addition of fibers modifies the behavior of fresh concrete, and particularly affects the packing density of aggregates. This document focuses on studying the shear behavior of self-compacting concrete reinforced with Steel fibers, but at the crack level. We evaluated crack resistance capacity by using different initial widths. To assess this, we designed a rigid steel frame to confine specimens, by restricting crack width and allowing block movement, so as to improve the stability and control of crack width. We verified functioning and sensitivity of this confinement system in order to know and assess the displacements that the specimen blocks undergo due to manipulation after precracking. An extensive experimental program was developed for over 60 specimens. The aims of this program were, adjusting the design and calibrate the general functioning of the restraint frame; define in detail an essay methodology; and finally, evaluate the possibility of detecting and interpreting different behaviors related to the type of material tested. The implementation of discreet measurement methodologies is also describe. Photogrammetry of crack width and triangulation with DEMEC were used. This implies that measurements were taken between the precracking phase and the push-off phase. The objective was to know the relative movements that the specimen underwent due to manipulation between both phases. From the results obtained, it was analyzed that the developed frame is capable of confining the specimen to carry out the push-off test, without interfering with slip displacement. It was evaluated that the shear stress transmitted through the restraint frame due to its vertical stiffness. On average, the restraint frame effect represents 10% of total theoretically calculated tension. A basic friction coeficient was defined that presents higher stability during the test. This friction coeficient was affected by a maximum aggregate size and aspect ratio.
