Experimental study on shear performance of wet joints with free-form surface shear keys in bridges

Wet joints in precast bridge decks are subjected to complex stresses and are vulnerable to cracking, with interface shear being a major damage mechanism. This study proposes a parametrically generated free-form surface shear key based on an even quartic interpolation profile. Hybrid CNC-machined aluminum templates and 3D-printed resin inserts were used to fabricate complementary convex and concave surfaces, and five plain- and reinforced-concrete specimens were tested under monotonic direct shear. Structural response was evaluated from crack patterns, load-displacement curves, and reinforcement strains, and a mechanics-based superposition model was established. Relative to the reinforced flat-joint specimen (RC-P), the convex and concave free-form specimens increased interface-debonding loads by 229.1% and 211.9%, respectively, and ultimate capacities by 100.5% and 105.8%, respectively. The smooth keys shifted failure from premature interface separation toward combined wet-joint crushing, diagonal substrate cracking, and reinforcement engagement. The proposed model, based on the projected-area resistance of the keys and the dowel action of reinforcement, gave a mean signed percentage error of −6.99% for the present specimens. For the external dataset, the mean signed percentage error was −0.02%. The broader contribution is a digitally manufacturable, continuously parameterized joint geometry together with an experimentally supported link among geometry, load-transfer evolution, and capacity prediction. Future research should quantify size effects, cyclic and fatigue behavior, and internal stress evolution through geometrically scaled tests and validated nonlinear finite-element simulations.