What is the main reason for prioritizing the retrofitting of columns over beams in certain seismic vulnerability scenarios?

The main reason for prioritizing the retrofitting of columns over beams in certain seismic vulnerability scenarios is to prevent a column-failure mechanism, which can lead to a catastrophic collapse of the structure. This prioritization is based on the concept of 'strong column-weak beam' design. Columns are the primary vertical load-carrying elements in a building, and their failure can compromise the stability of the entire structure. If columns fail before beams, the building can experience a soft-story collapse, where one or more stories collapse due to the loss of vertical support. Beams, on the other hand, are primarily responsible for transferring loads to the columns. While beam failure can cause localized damage, it is less likely to lead to a global collapse if the columns remain intact. By ensuring that the columns have sufficient strength and ductility to resist seismic forces, engineers aim to force plastic hinges to form in the beams rather than the columns. This allows the structure to dissipate energy through controlled yielding of the beams, while maintaining its overall stability. Therefore, retrofitting columns to increase their strength and ductility is often prioritized to prevent a brittle column failure and ensure life safety.