[niteshpant]

The useful life is less than RCC. A RCC structure is good for about 50 years, steel for 25. The 4x4 is even less, about 15 years.

No, you paint them initially when you build the structure. It's quite hard to paint afterwards.

Also, if you notice closely, the steel is welded rather than bolted. Newer buildings are bolted now-a-days, which increases their useful life.

Example: https://imgur.com/a/f4z84dx

This is the current building being built that I talk about. Notice (1) the two layers of paint, and (2) bolts being used instead of welds compared to the steel structure photos in the essay