Seismic performance of earthquake damaged beam-column sub-assemblages retrofitted with hybrid steel fibre reinforced concrete

Abstract

In this study, Hybrid Steel Fibre Reinforced Concrete (HSFRC) is used for retrofitting of earthquake damaged reinforced concrete beam-column sub-assemblage. HSFRC consisting of micro and macro steel fibres in 1:3 proportion is developed. It is noted that HSFRC with 1.5% of hybrid fibre content is suitable for retrofit application. Two deficient beam-column sub-assemblages conforming to olden seismic design philosophies are taken up for investigation. In order to simulate seismic damage, reverse cyclic loading is applied to beam-column sub-assemblages. The damaged beam-column sub-assemblages are retrofitted using HSFRC mixture in the disturbed region of the beam-column sub-assemblages. The retrofitted specimens are subjected to reverse cyclic loading. The seismic performance of post-earthquake retrofitted beam-column sub-assemblages are compared in terms of damage progression, load-displacement hysteresis behaviour, energy dissipation, and stiffness degradation. From comparative performance of sub-assemblages, it is observed that retrofitted specimen showed improved load carrying capacity but could not meet the ductility requirements of the sub-assemblages. This is due to the reversal of the strength hierarchy in the retrofitted specimens, leading to failure caused by bond degradation of the beam reinforcement bars in both positive and negative cycles of retrofitted specimens. Therefore, this study highlights the need for ensuring an appropriate strength hierarchy and adopting detailing such as fibre wrapping particularly at the construction joint, for achieving required strength and ductility for post-earthquake retrofitted specimens.