Title: RC Beams with Steel Fibres - Towards Better Determination of their Minimum Conventional Reinforcement Ratio
Author(s): Dancygier, A.N.; Karinski, Y.S.
Publication: Symposium Paper
Appears on pages(s): 246-253
Keywords: Cracking localization; Fibre-reinforced concrete; Flexural ductility; Minimum reinforcement ratio
Minimum longitudinal reinforcement ratio in reinforced concrete (RC) beams is determined
by criteria that refer to flexural capacity. However, relatively recent experiments have shown
that RC beams with steel fibres (RFRC beams) with the above-determined minimum
reinforcement, exhibit a pronounced reduction in their flexural ductility, compared with similar
plain RC beams. This phenomenon was characterized by cracking localization, when only one
or two cracks widened significantly more than the other cracks did. This led to increase of the
steel plastic strains, even up to its rupture, in the rebars that crossed these cracks. The ductility
reduction in this case impairs the structural response of RFRC beams compared with RC beams
without fibres. Therefore, this effect of the fibres must also be considered when determining
the minimum longitudinal reinforcement ratio in RFRC beams.
The paper presents analysis of test results that pertain to flexural ductility in RFRC beams
and its relation with the cracking localization phenomenon. This phenomenon may be
quantified by the ratio between the number of the significantly wide cracks and the total number
of flexural cracks. It is shown that RFRC beams with smaller reinforcement ratios had higher
cracking localization. It is also shown that as the reinforcement ratio decreases below a certain
value, which is considerably larger than the minimum required by the codes, the flexural
ductility decreases as well. Within this range of small reinforcement ratio, these two trends are
related, whereas for larger reinforcement ratios, there is no effect of cracking localization on
the flexural ductility.