Nothing really to add, sorry, but this reminds me of something I saw here in Tokyo once, just to show you the abuse the stairs take.
One of the main entrances to Shinjuku Station, just down the street, they were replacing the stair treads, I was really curious, as they were doing half the stairs at a time, so the foot traffic was rather congested on the other half of the stairs, and I remarked to my Japanese friend that it is a good thing they don't have to do that very often. He told me they do it about every year, maybe 18 months
The kicker is the stair treads were 3" thick granite, and in that short of a time, they get enough wear to have to replace them.......
3,000,000+ people a DAY go through Shinjuku station..., so that is 6,000,000 feet and that is an average day, so 365 x 6,000,000 = 21,900,000,000 boy that is a lot of foot steps
My point is that no matter what you do, stairs take a beating, and you have to be prepared to fix them up at some time.
The pessimist complains about the wind; the optimist expects it to change; the realist adjusts the sails.
William Arthur Ward