Influence of coating the steel tube on the bond strength between steel tube and concrete
© 2019 by the fib. All rights reserved. The behaviour of concrete columns reinforced with small diameter steel tubes (not reinforcing steel bars) has been investigated in recent years. Since the outer surfaces of steel tubes are smooth, the bond strength between steel tubes and concrete is highly critical, especially for the design of steel tube reinforced concrete columns. Coating the outer surface of steel tubes was proposed to prevent the slip of the steel tube in concrete. This study investigated the influence of coating the outer surface of steel tube on the bond strength between the steel tube and concrete. Coated and uncoated cold-formed steel tubes were used for testing the bond strength. The steel tube had a 26.9 mm outside diameter, 2.6 mm wall thickness and 250 MPa nominal tensile strength. Two different casting directions (vertical and horizontal) were used in casting concrete of coated and uncoated steel tubes. The bond strengths of the specimens were measured using pull-out tests. The test results indicated that for specimens cast horizontally, the average bond strength of coated steel tubes was 409% greater than the average bond strength of uncoated steel tubes. Also, for specimens cast vertically, the average bond strength of coated steel tubes was 433% greater than the average bond strength of uncoated steel tubes. Hence, the use of coated small diameter steel tubes enhances the performance of steel tube reinforced concrete members.