Concentrically and eccentrically loaded high-strength concrete columns with high-strength reinforcement: An experimental study

Abstract

The demand for high-strength steel (HSS) in concrete structures has been steadily increasing as it has potential to reduce congestion in heavily reinforced section, decrease steel quantity and lower the labour cost. Although typical design standards such as ACI 318 limit the design strength to 550 MPa, research focuses on developing design guidelines for using HSS. ACI ITG-6R-2010 has developed design procedures for the use of ASTM A1035 Grade 100 (690 MPa) steel bars as longitudinal reinforcement. ACI 318-2019 permits the use of 690 MPa bars as spiral transverse reinforcement in column. Australian Standards AS 3600-2018 allows HSS up to 600 MPa for longitudinal reinforcement and 800 MPa for transverse reinforcement (tie) in columns. While several design codes permit higher yield strength for steel bars, comprehensive test data are required to enhance the confidence in the application of the high-strength concrete (HSC) in conjunction with HSS in concrete columns. In this study, 39 HSC columns reinforced with HSS were tested under static loading. The compressive strength of concrete and yield strength of the longitudinal reinforcement varied between 100 and 115 MPa and 520–670 MPa, respectively, and tie was provided with 810 MPa steel. The ties were placed at a maximum spacing calculated based on AS 3600-2018 design model, resulting in 29% larger spacing than that for 500 MPa steel ties. The other test variables were section geometry, tie arrangement, tie bar areas and loading eccentricities. The columns section capacities were compared with AS 3600-2018 and ACI 318-2019 design models and ductility of the columns was studied too. It is shown that columns reinforced with HSS generally have a larger strength than that of the columns reinforced with 500 MPa Grade bars. The study also concluded that detailing HSS (810 MPa) tie reinforcement with HSS longitudinal bars meet the minimum confinement and the static ductility requirements of AS 3600-2018.