Influence of transverse steel configuration on post-elastic behaviour of high-strength reinforced concrete columns

Abstract

The influence of transverse steel configuration on the inelastic behaviour of high-strength reinforced concrete (HSRC) columns that were designed complying with the shear strength of BS 8110 (BS columns), the authors' proposed equation (NEW columns) and the provisions of Design Guidance for High Strength Concrete (BS' columns) has been studied experimentally. Totally ten (five pairs) HSRC columns having concrete cube strength from 57 to 111 MPa were fabricated and tested under various levels of compressive axial load as well as reversed cyclic inelastic displacement excursions. Each pair of the columns contained almost identical cross-sectional properties, including concrete strength, applied compressive axial load level, content of longitudinal steel and transverse steel, except the configuration of transverse steel. In the BS columns (two pairs) as well as the NEW columns (two pairs), one of the columns in each pair contained intermediate cross ties along with single closed square hoops, which formed the transverse steel of the other column of the same pair. All end hooks of the transverse steel were bent 90° in the BS columns, but 135° (forming 45° angle) in the NEW columns. In the BS' columns, both of them contained intermediate cross ties in addition to single closed square hoops, but their end hooks were bent 90° in one of the columns and 135° in the other column. It was evident from the results that: (1) the NEW columns with cross ties had ultimate deformability superior than their counterparts without cross ties, (2) adverse effects in flexural strength and ductility were found in the BS columns containing cross ties with moderate amount of longitudinal steel due to large transverse steel spacing, (3) 45° end hooks effectively delayed the inelastic buckling of longitudinal steel, and (4) all the NEW columns behaved in a limited ductile manner.