Thin-walled structures are particularly advantageous for applications that require lightweight designs with high stiffness and strength. Therefore, understanding their mechanical behavior is essential. Internally stiffened thin-walled structures are of particular interest, as internal reinforcements can be designed to optimize the moment of inertia, leading to increased stiffness and strength. This investigation applies structural finite element analysis (FEA) to assess the strength behavior of internally reinforced hollow-box beams. A total of twelve different beams were subjected to static three-point bending stresses, with loads applied to beams that had previously undergone stiffness optimization for enhanced performance. These beams were carefully modified to achieve the highest possible stiffness while minimizing mass. The strength was evaluated using von Mises equivalent stress values, and various metrics were provided to analyze the behavior of the optimized models. The optimized beams were compared with both the initial models and a reference model of an unstiffened beam to assess the impact of stiffness-based optimization on strength results. The findings indicate that the optimization technique, originally developed to increase stiffness while reducing mass, also improves specific strength while maintaining mass reduction. The primary benefit of reducing material in certain parts is not only the decrease in material costs but also the enhanced motion capability of mobile components, which allows for faster movement. The technological complexity of producing such structures was high until recent years, when additive manufacturing emerged as an affordable and high-quality solution for fabricating complex parts like those studied here. Future research could focus on exploring the long-term stability and safety of these structures.