Purpose <p>This study analyzes the buckling behavior of porous bi-directionally functionally graded (Bi-FGM) nanobeams subjected to two successive moving masses, focusing on how varying material properties and environmental conditions influenced the mechanical performance of these advanced lightweight structures under complex loading scenarios.</p> Methods <p>A theoretical framework is established by incorporating the virtual work principle with a two-phase local/nonlocal strain gradient theory. The governing equations are formulated for beams under uniform, linear and sinusoidal hygrothermal conditions, with particular emphasis on simply supported (S–S) beams and configurations incorporating intermediate supports. Convergence studies, performed using the higher-order Haar wavelet method (HOHWM) and the generalized differential quadrature method (GDQM), validate the model's accuracy.</p> Results <p>Key findings indicate that the ceramic volume fraction and hygrothermal conditions are critical in determining the stiffness and buckling response of Bi-FGM nanobeams. Clamped–clamped (C–C) boundary conditions offer the greatest resistance to buckling, while linear hygrothermal profiles enhance stability. In contrast, uneven porosity distributions reduce buckling resistance significantly. Additionally, nonlocal parameters decrease the critical buckling load, whereas higher strain gradient values improve beam stiffness. Intermediate simply supported configurations display both softening and hardening effects, depending on the environmental conditions.</p> Conclusion <p>The results underscore the importance of optimizing material gradation, boundary conditions, and environmental factors for improving the structural performance of Bi-FGM nanobeams. This study provides valuable insights that can inform the design of more resilient and high-performance nanobeams for advanced engineering applications in hygrothermal environments.</p>