Drift capacity of rectangular reinforced concrete columns with low lateral confinement and high-axial load

This paper presents the experimental results obtained from the testing of nine 1:3 scale square-shaped column specimens. Characteristics of the specimens are low-lateral confinement, low-to-moderate shear span, and high- axial load. Detailing of the transverse reinforcement includes both 90° and 135° hooks. Specimens with low-shear span failed under shear in a brittle manner. Flexural failures were observed in specimens with moderate shear span and having a lateral confinement ratio of 0.003. Lateral confinement has significant influence on the ultimate drift, of which an increase from 0.001 to 0.003 could increase the ultimate drift capacity by up to 100%. Seismic performance of columns with low-to-moderate shear span may not be accurately reflected by the ductility factor. Better representation is provided by the ultimate drift ratio, and can be estimated by an empirical equation. The use of 90° hooks in detailing the transverse reinforcement leads to a 40% reduction on the ultimate drift capacity. Guidelines are also given to estimate the corresponding reduction on the ductility factor.