This paper aims to study the composite action on web-post buckling (WPB) resistance of composite cellular beams with precast hollow core slab (PCHCS) units and with precast hollow core slab units with concrete topping (PCHCSCT). Geometrical and material non-linear analyses are performed. A parametric study is developed, varying the opening diameter, the web-post width and the shear stud spacing, with single and double row. It was found that the models with double row of shear studs showed global shear resistance greater than or equal to the models with only one row. For models with PCHCS, there was a reduction in global shear resistance in some analyses due to the absence of shear studs in the second opening, close to the support. For PCHCSCT models, there was an increase in the global shear resistance, in comparison with PCHCS models. However, in most of these models, shear stud rupture occurred. Finally, the WPB models were compared with a simplified equation that takes into account the global shear resistance due to buckling, composite action and Vierendeel bending. The average, standard deviation and variation value of the ratio between the analytical and numerical models were 0.833, 12.47% and 1.55%, respectively.