Experimental study on the minimum limit anchorage length and mechanical properties of bent anchorage steel bars in reactor building

Abstract

This study presents a comprehensive investigation into the anchorage performance of bent steel bars embedded in straight segments of reinforced concrete (RC) specimens with high reinforcement ratios, using a prototype nuclear reactor shear wall as the reference model. A total of 44 pull-out tests, grouped into nine series, were conducted to determine the minimum effective anchorage length. Key failure mechanisms, bond behavior, and strain development were systematically analyzed. The results indicated that with decreasing anchorage length, no pull-out failure occurred; instead, steel bar fracture became the dominant failure mode. The minimum effective anchorage length was identified as 0.25l_ab_e, below which anchorage performance was significantly compromised. At this critical length, the incorporation of structural transverse reinforcement increased the average maximum yield load by 4.96 %, whereas variations in bent bar length exhibited minimal influence. Furthermore, high reinforcement ratios enhanced the deformation capacity of the specimens, reducing the likelihood of premature yielding. Specimens without transverse reinforcement exhibited a 32.08 % reduction in average yield displacement (9.95 mm) compared to those with transverse reinforcement. An empirical regression model was developed to modify the bond strength calculation under high reinforcement conditions, exhibiting strong predictive accuracy and aligning closely with experimental observations. The findings offer practical insights for the anchorage design of RC specimens in nuclear facilities, especially under conditions of dense reinforcement where existing code provisions may be inadequate.