During the construction of reinforced concrete buildings, formwork supports often adopt single-layer structural systems, double-layer structural systems, or steel scaffolding structural systems combined with other shores, depending on the internal height of the buildings. Although each structural system differs, they are all influenced by the same failure mechanism, the leaning column effect, which impacts their critical loads. This study examines the impact of this failure mechanism on the critical loads of these three types of formwork supports during the construction of reinforced concrete buildings. The research findings indicate that when the entire structural system buckles, the leaning columns in the structural system induce additional horizontal forces due to the failure mechanism known as the leaning column effect. This horizontal force will decrease the overall buckling load of these three types of structural systems. Adding leaning columns to single-layer structural systems, double-layer structural systems, and steel scaffolding systems combined with other shores will not increase their critical loads. If the failure mechanism is not considered during the design of the formwork support structure, there is a high risk of support collapse.