Static Behavior of Structural Elements made of High Strength ...

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29 Νοε 2013 (πριν από 3 χρόνια και 9 μήνες)

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Static Behavior of Structural Elements made of High
Strength Steel Fiber Reinforced Concrete– Stage 2:
Anchorage at supports and direct tension

Assoc. Prof. Amnon Katz, Assoc. Prof. Avi Dancygier



ABSTRACT

This study examines the influence of concrete strength and of the use of steel fibers
on bond between deformed rebars and concrete and on the tensile behavior of steel
rebar embedded in fiber reinforced concrete (FRC). The current phase of the study
focuses on bond in the beam region located over a direct support, and direct tension
behaviour of reinforcing bars embedded in FRC. The previous stage of the study
focused on bond under direct pullout and flexural pullout, where the bonded part of
the tested rebar was located near mid-span of the beam. ,.
Research goals included study of the bond capacity and behavior of deformed
rebars in 'non-regular' concrete, that is, concrete of high compressive strength (HSC)
and concrete that includes steel fibers. Thus, specimens were made of plain and fiber
reinforced concrete at two strength levels: normal and high strength (NSC, FNSC,
HSC and FHSC). Nominal compressive strengths of NSC and HSC specimens were
about 30 and 100 MPa (referring to 100-mm cubes at 28 days). The FRC specimens
included 30-mm hooked-end steel fibers at a constant volume ratio of 0.75%. The
tested bar diameters were 12 and 20 mm. The pullout tests were based on the
standard RILEM flexural bond test (“beam test”) of deformed steel bars, with
modifications that were pertinent to the scope of this study.
Chapter 2 of this report presents a literature background, followed by a description
of the pullout tests (Chapter 3) and of the direct tension tests (Chapter 4). The report
also includes an analysis of the results. The main conclusions from the pullout tests
refer to the effects on bond of concrete strength, of fibers and of the location of the
bonded rebar (over a support or near mid-span). The analysis also included
examination of the rebar-concrete slip, which affects energy absorption related to the

pullout process. Additionally, bond strengths that were measured were compared to
design strengths provided by the Israeli, European and American codes. Special
attention was given in these comparisons to the experimental-to-design ratios (EDR)
obtained in the regular concrete specimens and EDR values of the non-regular
specimens.
The effects of steel fibers on the post-cracking concrete strength and on the
cracking pattern (crack control) were studied in direct tension tests of RC and FRC
prisms. It was observed that for both NSC and HSC, application of steel fibers with a
low amount of conventional reinforcement (deformed rebars) caused localization of
tension strains and hence larger local cracks. It is noted that this type of behavior may
lead to reduced ductility.