الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
In recent years, high strength concrete HSC has found many application not only in columns of high-rise building, but also in abroad range of long-span flexural members. However, the maximum potentiality of HSC connot be fully realized in structures due to the brittleness of the material and the serviceability problems associated with the resulting reduced cross sectional dimensions. In the present work, the effect of steel fibers inclusion on the flexural behavior of HSC beams is investigated under monotonic ststic loading. Comprehensive experimental program study was performed to study the different flexural response characteristics of high strength fiber reinforced concrete HSFRC beams with different fiber contents and aspect ratios, fibers cocktail, and fiber zoning. Finally, semi-empirical formulae were developed for the ultimate analysis and design of HSFRC beams in bending.
In the experimental program, eleven simply-supported beams were tested under two symmetrically concentrated loads. All beams were reinforced by high-strength tensile steel bars as tension reinforcement, mild steel bars as secondary steel, and vertical mild steel stirrups as web reinforcement. The mean compressive strength of concrete matrix was 80 MPa. Using under-reinforced section approach, the longitudinal tension steel ratio was evaluated as 0.87%. The research objectives were to study the effects of fibers inclusion on the load-carrying and moment-resisting capacities, flexural stiffness, load-deflection curves, load-steel strain relationships, displacement and strian ductilities, failure mechanisms, and crack propagation and width. Moreover, the measured load-displcement response of the tested beams was used to define several indices to measure the flexural toughness of HSFRC at different loading levels.
The effects of different fiber volume fractions, fiber aspect ratios, depths of fiber inclusion zones, and polypropylene-steel fibers coctail were studied on the flexural response. The testing results indicated that the flextural strength and toughness, displcement ductility, steel strian ductility, and secant stiffness, increas considerably with the increase of fiber content or fiber aspect volume from 0.0% to 2.0 % leads to an increas in ultimate moment by 21.0% in displacement ductility by 17.0% in toughness by 77.0% and in steel-strain ductility by 49.0% the increase of fiber aspect ratio from 50 to 80 leads to an increase in ultimate moment by 20.0% in displacement ductility by 15.0%, in toughness by 68.0%, and in steel-strain ductility by 41.0%. the use of 2.0% fiber content reduces the crack width by 29.0% and the use of fiber aspect ratio 80 with fiber volume 1.0% decreases the crack width by 30.0% the flexural response of the partially reinforced fiberous beams , where included only in the tension zone, was close to that of the fully reinforced fiberous beams. The addition of polypropylene fibers to HSFRC beams has a minor effect on the improvement of the measured structural response.
Based on strain compatibility and equilibrium conditions for HSFRC sections in joint with idealized compression and tension stress blocks, simple formula were developed for the ultimate flexural strength analysis and design of HSFRC beams. The stress blocks were given by suitable empirical function for the compressive and post-cracking strengths of HSFRC.The accuracy of the proposed procedure was checked by comparing the calulated flexural strengths with the measured results and with the experimental data reported in the literature. A very good correlation was found for different concrete strengths, steel reinforcement ratios, steel fiber parameters. and different sizes of beam specimens.