Numerical Investigation of the Interfacial Shear Behavior of Grooved UHPC–NC Composite Members.

Prefabricated ultra-high performance concrete (UHPC) combined with cast-in-situ normal concrete (NC) enables durable, high-performance composite members, but its reliability is governed by the bond at the UHPC–NC interface, where debonding between prefabricated UHPC plates or formwork and the adjoining NC is repeatedly reported. Prior work has largely pursued surface roughening or post-installed studs developed for UHPC repair overlays; the systematic optimization of groove geometry for prefabricated-UHPC-with-cast-NC members remains unaddressed. This study develops a three-dimensional nonlinear finite-element model in ABAQUS and validates it against two independent experimental programs—Z-shaped direct shear and push-out specimens—reproducing the measured failure modes, load–displacement responses, and interface shear strengths. The validated model then drives a parametric study of grooved interfaces spanning groove angle (45°–90°), depth, width, spacing, and number, and hence groove density, benchmarked against a monolithic control (ultimate load 150.63 kN, shear strength 5.02 MPa). Beyond ranking sensitivities, the results reveal a change in failure mechanism: grooving shifts failure away from the interface and into the NC adjacent to it, engaging a shear-key action with no scaling-off between the UHPC and NC, and converts the brittle, sudden failure characteristic of merely roughened interfaces into a markedly more ductile response. Groove number and angle exert the strongest influence: a five-groove interface raised the shear capacity to 277.83 kN (9.26 MPa), about 84% above the monolithic control, while an intermediate 75° groove angle proved optimal—exceeding the 90° groove—and groove spacing had comparatively minor effect. These findings recast groove design as a means of controlling failure mode and ductility, not merely capacity, and offer practical rules for detailing robust UHPC–NC interfaces.