Cyclic testing of reinforced concrete columns with double or one-side headed shear reinforcement

Abstract

The effectiveness of single-leg crossties that were anchored by heads in reinforced concrete columns was assessed. Seven reinforced concrete columns were tested under reversed cyclic loading with a 10 % axial load of the nominal axial capacity of the columns. Four columns were designed to fail in a flexural mode, and three columns were designed to fail in a shear mode. The main variable was the anchorage type of crossties: conventional crossties that were anchored with 135° and 90° hooks, crossties that were anchored with one-side head and one-side 180° hook, and crossties that were anchored with double heads. The test results indicate that the hysteretic behavior of the columns with crossties that were anchored by double heads or one-side head was similar or superior to the columns with conventional crossties anchored by hooks in terms of ductility and energy dissipation. After the cover concrete spalled, the 90° hooks inevitably opened and the column longitudinal bars buckled. However, the heads could delay the buckling of the column bars and the columns could maintain their capacities until 8 % drift ratio for the columns that were designed to fail in a flexural mode. For the columns that were designed to fail in a shear mode, all columns showed similar behaviors and had identical strengths. The columns with the headed crossties had smaller crack widths than the columns with conventional crossties because the headed crossties well confined the core concrete under severe shear deformation. The test results show that headed crossties can effectively confine the column bars and core concrete of the columns: therefore, the ductility and energy dissipation capacity of the columns were improved.