Abstract
Reinforced concrete (RC) columns of old existing buildings are vulnerable to earthquakes because the hoops comprising their transverse reinforcement are widely spaced and anchored using 90° hooks. This study extensively evaluated the seismic behavior of RC columns with such non-seismic details. Experiments were conducted by applying lateral cyclic loads to five full-scale column specimens with various transverse reinforcement details subjected to low axial loads. The experimental results demonstrated that the internal transverse crosstie had a significant confinement effect in the non-seismic detailed columns with 90° hoop anchor hooks. In addition, the lateral load–drift relationships, ductilities, and energy dissipation capabilities of the columns were not significantly affected by the hoop spacing or anchor hook angle when a low axial load was applied up to a drift ratio of 3.5% before failure. The evaluation model based on ASCE/SEI 41-17 was then shown to approximate the initial stiffness, maximum strength, and post-peak strength reduction behavior of the non-seismically reinforced column. This study was based on the experimental behavior of single column members, and it needs to be extended to research on frame structures in which columns are connected to beams and slabs.
Highlights
Reinforced concrete (RC) buildings constructed before the application of seismic design standards or in areas with low earthquake prevalence mostly have non-seismic details that are vulnerable to earthquake damage
These results confirm that the volumetric ratio of transverse reinforcement exerts a greater effect on μ than the angle of the hoop anchor hooks in buildings subjected to low axial load
Existing RC buildings to which seismic design is not applied have non-seismic details that are vulnerable to earthquake damage
Summary
Reinforced concrete (RC) buildings constructed before the application of seismic design standards or in areas with low earthquake prevalence mostly have non-seismic details that are vulnerable to earthquake damage. Lam et al conducted experiments on 1/3-scale RC columns with non-seismic details using axial load, shear span-to-depth ratio, and transverse reinforcement hook angle as variables. The effect of hoop anchor hook angle on RC columns subjected to low compressive forces has been observed to vary depending on the axial force ratio and the spacing of transverse reinforcements, but further clarification of the effects corresponding to the changes in these variables is needed. Against this background, the seismic behavior of RC columns with non-seismic details subjected to low axial loads—such as typically found in old existing buildings—were thoroughly evaluated in this study.
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