Studies on the pull-out strength of ribbed bars in high-strength concrete

The transfer of forces from reinforcing bars to surrounding concrete in reinforced concrete (RC) is influenced by many parameters. Several efforts were made to understand the influence of bond on global behaviour of RC members. However, the information on bond strength of high strength concrete (HSC) is lacking. An attempt was made to study the influence of various parameters on bond such as bar diameter, strength of concrete, lateral confinement and embedment length. The bond lengths were 50 mm and 150 mm with different bar diameters, strength of concrete and type of confinement. The bar diameters were 16 mm and 20 mm. The bars were embedded in concrete without confinement and with confinement using spirals and ties. The casting was done keeping the bars in the horizontal position. The anchorage bond specimens were tested using displacement control system and the slip of the bars was controlled at a rate of 1.51 mm/minute (0.025 mm/second). The bond stress-slip response was studied by varying the variables. As the strength of concrete increases the slip at failure decreases in the descending branch. With smaller bond length, the bond stress was found to be higher. The bond strength was found to decrease as the bar diameter increased. Splitting failure was observed in unconf ined specimens, whereas pullout failure in confined specimens. The ultimate bond strength ranges between 10.8 MPa and 19MPa with spiral confinement, whereas it ranges between 9.2 to 16MPa with tied reinforcement. The ductility was found to increase with spiral reinforcement. © 2007 Taylor & Francis Group.