Experimental study of cyclic behavior of high-strength reinforced concrete columns with different transverse reinforcement detailing configurations

Detailing of transverse reinforcement is essential to ensure ductile behavior of reinforced concrete (RC) members, particularly for columns with large displacement demanding under high axial loading level. Requirements of reinforcing details are even important for high strength concrete due to its brittleness nature. This paper presents experimental study regarding cyclic behavior of high strength RC columns with different transverse reinforcement detailing layouts. The three high strength RC columns consisted of different transverse reinforcement detailing configurations, which were conventional closed-hoops, butt-welded hoops and single closed-hoop with cross-ties, respectively. The columns were made of high-strength concrete with compressive strength of 70 MPa and high-strength steel with yield stresses of 685 MPa and 785 MPa for longitudinal and transverse reinforcement, respectively. Cyclic displacement static tests subjected to high axial compression loading of 0.3Agf′c were conducted to verify the adequacy of transverse detailing. The performance of the column with conventional closed-hoops and that of the column with butt-welded hoops, which were compliant of ACI 318-14, were almost identical and met the performance criteria required by ACI 374. In contrast, the column with a single closed-hoop and cross-tie that was designed based on ACI 318-11 did not perform well as a ductile RC column. These results prove that the ACI 318-14 minimum requirements for confinement should be followed. In addition, butt-welded hoops are acceptable as a form of transverse reinforcement of a column, since no fracture was observed at the welded location. The current flexural and shear design equations for the RC columns are discussed and compared with the test results.