Vibration and buckling analysis of quasi-3D porous composite steel-polymer concrete box section beams via DQFEM

This paper presents a dynamic and critical buckling analysis of hollow steel boxsection beams infilled with a porous polymer concrete composite core, modeled using a refined quasi-3D beam theory. The study investigates the effects of porosity in the polymer concrete core on the mechanical behavior of the beam. The governing equations are derived using the Differential Quadrature Finite Element Method (DQFEM) combined with Lagrange’s principle. Results show that hollow steel-only beams exhibit the highest natural frequencies, while adding a composite core slightly reduces frequencies due to increased mass. Introducing porosity further lowers the frequencies, with a uniform porosity distribution (UDP) achieving better performance than nonuniform distributions. Increasing the slenderness ratio enhances natural frequencies across all configurations. For critical buckling loads, a solid (non-porous) core provides the highest capacity, while porosity reduces the load-bearing capacity compared to the solid core; however, UDP outperforms non-uniform distributions. Non-uniform porosity patterns demonstrate advantages in preserving structural integrity under certain conditions. The effects of slenderness ratio and boundary conditions are also examined, highlighting their influence on dynamic and stability responses. The model is validated through comparisons with numerical and experimental results from the literature, demonstrating high accuracy. These findings provide valuable insights into the dynamic and buckling behavior of porous composite beams and offer practical guidelines for designing porous material-based structures in engineering applications.