Showing papers by "Antonio Nanni published in 1991"

Fiber-Optic Sensors for Concrete Strain-Stress Measurement

Abstract: The paper presents a nondestructive testing method based on fiber optics for measuring strain and stress in concrete structures in situ. When an optical fiber is embedded in concrete, and its refractive index, dimension, and/or shape are changed as a result of the surrounding matrix deformation, the characteristics of the light signal transmitted along the fiber are modified. Optical techniques capable of determining the changes in light characteristics are described. The two most promising techniques for concrete-structures diagnostics are demonstrated in the laboratory using concrete cylinders subjected to unconfined uniaxial compression with optical fibers embedded in a direction parallel and perpendicular to the aplied strain (load). Encouraging experimental results indicate that fiber-optic sensors can be a feasible tool to determine strain/stress distribution in buildings and infrastructures.

Fatigue behaviour of steel fiber reinforced concrete

Abstract: The results of an experimental investigation on the fatigue characteristics and residual strength of steel fiber reinforced concrete (SFRC) are reported. The testing program included flexural specimens as well as split-cylinders and cubes reinforced with two fiber types at a low volume content. One of the fibers was of the deformed slit-sheet type available at aspect ratios of 45 and 60. It is shown that SFRC has a better fatigue response than plain concrete and that the deformed slit-sheet fiber has an effect almost identical to hooked-end fiber of similar dimensions. There is no increase in residual strength measured by split-tension when specimens are subjected to fatigue stress above the endurance limit. Fatigue characteristics of SFRC from this testing program as well as previous works can be interpreted as a function of the fiber factor (i.e. a parameter accounting for volume fraction, aspect ratio and fiber type) to provide design charts. More experimental work is needed to provide an acceptable database for fatigue design of SFRC.

Distribution and opening of fibrillated polypropylene fibers in concrete

Abstract: The paper reports on the effect of fibre type, matrix workability, and mixer type on the distribution and opening of collated fibrillated polypropylene fibers used as concrete reinforcement. By means of the wash-out test method and within the limitations of the experimental program, it is demonstrated that: twisted fibers ere more likely to open than straight fibers in a zero-slump matrix, fiber distribution and opening is easier in a slumpable matrix than in a zero-slump matrix, and high-intensity mixers are more efficient than low-intensity ones even if they tend to shear a larger number of fibers. The investigation was limited to laboratory-type equipment.

Pseudoductility of fiber reinforced concrete

Abstract: This paper presents the findings of an investigation to determine the load‐deformation response of fiber reinforced concrete (FRC) subjected to standard flexural (ASTM C‐1018) and split‐tension (ASTM C‐496) tests with the objective of studying the correspondence between the FRC tensile properties obtained with the two methods. This comparison is desirable since split‐tension performed on cores or cylinders could be preferable to the more common flexure test with regard to ease of specimen collection or fabrication, and testing. In this study, a total of 17 fiber types from the United States, Europe, and Japan are used at two or more different volume contents. In terms of pseudoductility, it is found that the flexural test effectively differentiates between fiber content and type. On the contrary, the instrumented split‐tension test, with deformation measured along the horizontal diameter (perpendicular to the load plane), shows a flat postcracking response that is almost independent of fiber content and t...