The existing analysis models for torsional strength or torsional behavior of steel fiber reinforced concrete (SFRC) members typically adopted a simple approach, in which the tensile constitutive model of conventional concrete was modified appropriately for the SFRC considering that the steel fibers and concrete matrix behave in a fully composite manner. In such approaches, however, the pull-out behavior of the steel fibers at crack interfaces caused by the progressive loss of bond stress developed between the fiber and surrounding concrete is hard to be described in detail, and they also requires much experimental effort and cost to derive the constitutive models of SFRCs in tension for various types of SFRCs. In this study, steel fibers are modeled as separate direct tension force transfer elements and applied to a modified fixed-angle smeared-crack truss model for torsion so that the bond mechanism between the steel fibers and concrete matrix can be reflected in the tensile behavior of SFRC further in detail. The proposed fixed-angle model approach for torsional behavior of SFRC members take into account the difference between principal stress and cracking angle, and well reflects the unique characteristics of SFRC, such as fiber directionality and bond mechanism. The proposed approach provided a good agreement with the torsional behavior of 48 specimens obtained from previous studies.
The compressive strength, permeability and hydraulic diffusivity of Ordinary Portland Cement (OPC) with or without pozzolana blended concrete have been estimated in this investigation by using Mercury Intrusion Porosimetry (MIP). With this in view, concrete cubical specimens were crushed and the broken chunks with aggregates were collected from different mixes such as OPC mix, OPC with silica fume (5%, 10% and 15% of replacements) mix and OPC with slag (10%, 30% and 50% of replacements) mixes. The MIP experimentation was carried out for wide range of curing ages such as 1, 3, 7, 28, 42 and 90 days. The experimental Pore Size Distribution (PSD) parameters such as mean distribution radius (r0.5), dispersion coefficient (d) and permeable porosity (P) for all mixes were calculated by using the Morgan Mercer Flodin (MMF) model. The application of experimental PSD parameters is demonstrated by estimating the com-pressive strength, permeability and hydraulic diffusivity through the readily available corresponding relationships in the literature. It is observed that the lowest r0.5 and high d values are obtained in case of OPC with silica fume mix as com-pared to other mixes owing to its better pore refinement. It is observed that the estimated permeability increases with an increase in w/c ratio and decreases with an increase in curing ages which resembles the trend of Powers’ permeability versus w/c ratio curves.
This paper describes an experimental and numerical investigation into the effect of reinforcement exposure during the patch repair process on the ultimate strength of continuous beams. The parameters investigated were the position of breakout within the member and the areas of flexural reinforcement at the intermediate support and within the span. Reinforcement layouts were designed to vary both the moment redistribution demand for the full plastic collapse load to be attained and the redistribution capacity at the location where the first hinge would form. Exposure of reinforcement and the consequent loss of bond has two major effects. Firstly, it reduces beam stiffness at the exposed location, and shifts the balance of moments away from the location at which bars are exposed to other parts of the beam, Secondly, loss of composite interaction alters the pattern of flexural strains at the exposed section, increasing the strain at the extreme compression fibre and reducing section ductility. Results show that the moment capacity of a section with reinforcement exposed is not reduced if the exposed reinforcement yields before concrete crushing, but reductions in ultimate flexural strength are likely in heavily reinforced and therefore less ductile sections.
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