Reinforcement Strategies for 3D-Printed Structures: A Structural Behavior-Based Review

Structural reinforcement is essential for overcoming the limitations associated with layer-by-layer construction in 3D printing. However, existing studies typically evaluate reinforcement techniques as isolated solutions, limiting a unified understanding of how different reinforcement mechanisms contribute to structural performance. This review proposes a multiscale conceptual framework that classifies reinforcement strategies according to the structural scale at which they operate and the failure mechanisms they address. The literature on reinforcement approaches was systematically analyzed and organized into four structural scales: material, interface, element, and system. Furthermore, their influence on compressive, flexural, and shear behavior, along with anisotropy mitigation, was comparatively evaluated. The analysis shows that each reinforcement scale performs a distinct structural function. Material-scale reinforcement primarily controls cracking, while interface-scale reinforcement improves interlayer stress transfer and mitigates anisotropy. Element-scale reinforcement provides continuous load paths and increases load-bearing capacity, whereas system-scale reinforcement modifies global load distribution and structural response. These findings indicate that no single reinforcement scale addresses all the structural deficiencies associated with 3D-printed structures, highlighting the importance of interactions among complementary mechanisms across scales. The proposed framework relates reinforcement strategies to structural demands and governing failure mechanisms. The analysis identifies hybrid reinforcement systems, standardized evaluation procedures, multiscale modeling, and design methodologies as key directions for developing reinforced 3D-printed structures.