Experimental Study on the Bonding Behavior between Ribbed Steel Bars and Ultra-High-Performance Concrete

To evaluate the bonding behavior between ribbed steel bars and ultra-high-performance concrete (UHPC), several pull-out samples were experimentally investigated and presented. The influences of bar diameter and embedment length on the bond failure mode, ultimate bond stress, stress?slip curve and bond stress distribution were investigated. Compared with that of ordinary reinforced concrete, the ultimate bond stress between steel bars and UHPC was increased by 74% under the same conditions. In addition, the bond-slip curve showed a relatively large slope before the ultimate bond stress was reached, and at the same time, the curve showed better ductility after the ultimate bond stress was exceeded. When the sample experiences steel bar yielding or pull-out failure, the bond stress distribution curve exhibits typical multipeak features. As the bar embedment length increased, the bond stress distribution became increasingly heterogeneous, and the increase in the peak number in the bond stress distribution curve reflected this trend. Under appropriate concrete cover thickness, the critical embedment length was between 4d and 6d.