Experimental and numerical investigation of bond conditions in reinforced concrete half-joints

Dapped-end connections are widely used in precast concrete buildings and Gerber-type bridges. While the sudden reduction of depth at a sharp re-entrant corner lends itself to convenient precast construction, it also creates stress concentrations leading to early formation of corner cracks under service conditions. Further widening of these inclined cracks promotes localised bond deterioration caused by micro-cracking and reinforcement pull-out. This study investigates the influence of bond deterioration on the strength and the behaviour of dapped-end connections through four large-scale experimental tests, consisting of a reference specimen with ribbed reinforcement, a specimen with plain bars and two specimens with locally de-bonded hanger and flexural reinforcement near the re-entrant corner to idealise bond deterioration. Digital image correlation was employed to capture full-field deformations of the connections, enabling detailed assessment of crack kinematics and aggregate interlock behaviour. The results show that bond deterioration significantly alters load transfer, crack propagation, failure modes, and rotational behaviour of the connection. Specimens with de-bonded reinforcement exhibited reduced reinforcement engagement and a transition towards a more brittle shear-dominated response, while the specimen with plain bars failed by reinforcement pull-out. Aggregate interlock contributed significantly to shear transfer near the crack tip and along secondary shear cracks; however, its contribution to the main corner crack was limited due to large crack openings. Nonlinear finite element analyses using VecTor2 software accurately reproduced the experimental response, predicting peak resistance with an average experimental-to-predicted strength ratio of 1.01. Thrust line analyses confirmed good agreement between experimentally derived and numerically predicted flow of forces. • Reports experimental research of four large-scale dapped-end connections. • Detailed measurements of local and global deformations are provided. • Numerical simulations were performed to further investigate the behaviour. • Digital image correlation quantified crack widths and aggregate interlock forces. • Flow of internal forces of test specimens are analysed with FEM and trust line.