<p>To improve the dynamic bending performance of civil engineering protective structures while maintaining overall lightweight characteristics, this study proposes a design of thin-walled square tubes filled with foam concrete as the core material. The flexural behavior of these structures incorporating foam concrete with different densities was investigated through quasi-static and low-velocity impact three-point bending tests. The incorporation of foam-concrete filling enhances the mean crush force of thin-walled tubes by up to 88% in quasi-static bending and by 80% in dynamic bending. The quasi-static behavior involves both local indentation and global bending, whereas the dynamic response is dominated by local indentation. Numerical simulations were further performed to investigate the effects of wall thickness, core filling ratio, span length, and impact velocity on flexural performance. The interaction between the foam concrete core and tube wall, along with their collaborative deformation under different conditions, was clarified. Moreover, based on the bending-indentation theory of hollow tubes, the flexural response of foam concrete-filled tubes under static loading is derived and validated against experimental results.</p>