Experimental Study on the Performance of Lap-Spliced Steel Bars in Ultrahigh-Performance Concrete

Ultrahigh-performance concrete (UHPC) is a new cementitious composite material that exhibits a high bond strength with steel reinforcement. To investigate the splice performance levels of steel bars in UHPC, mutual pullout tests on lap-spliced specimens and direct central pullout tests on bond-anchorage specimens were conducted in this work. The main variables included loading mode, concrete cover, and steel bar position. The results showed that the splice strength of lap-spliced steel bars was approximately 0.76 times the bond strength of the anchored steel bar with the same bond length. The splice strengths of specimens under one-way repeated loading were lower than those under monotonic loading; increasing the splice length or concrete cover thickness reduced the weakening effect of one-way repeated loading on lap-spliced specimen performance. The concrete cover thickness showed a strong positive linear correlation with the splice strength in the range of 0.75d(b) to 2.25d(b) and played an important role in stopping crack development in the specimens. The splice strengths decreased when the loading steel bar was moved from the middle of the structure to the side. Based on the experimental results, formulas for the splice strength and critical splice length of lap-spliced steel bars in UHPC under monotonic loading and one-way repeated loading are suggested. Finally, an analytical model for the bond slip of lap-spliced steel bars is proposed, providing a good fit with the test results. (c) 2023 American Society of Civil Engineers.