Impact on the number of floors of a reinforced concrete building subjected to sudden column removal

• β index determines the condition of columns after instantaneous column removal.
• Columns should be rehabilitated for existing tall buildings subjected to sudden column removal.
• Beams are more vulnerable for short buildings due to instant column removal.
• Axial impacts for neighbor columns is increased, when the number of floors is increased.
• λ index shows the gravity stiffness reduction rate.

In recent decades, there have been many reports of buildings collapsing due to incidents such as gas explosions, terrorist attacks, and vehicle accidents. The goal of this paper is to present the findings of a study of the how the number of stories of a reinforced concrete (R.C.) structure impacts the building when a first-story column is removed instantaneously. Three R.C. buildings were studied, all of the same plan, but with varying numbers of floors (3, 5, and 7 floors). The criteria established for comparing the behavior of the buildings when sudden column removal occurs are (1) performance level of the beams, (2) gravity stiffness of the buildings, and (3) variations of applied axial forces to the columns. The Column Sensitivity Index (β) was utilized to compare the condition of neighboring columns before and after the column removal. The results of the study showed that the β increases when the number of floors increases, which means that the neighboring columns are more vulnerable to damage. On the other hand, when the number of floors increases, the performance level of the beams improves, and the number of created moment plastic hinges in the beams decreases. The Displacement Sensitivity Index (λ) was generated to compare the gravity stiffness of the structures at the top node of the removed column before and after column removal. The results showed that the reduction rate of the gravity stiffness decreased when the number of floors increased.