I'm not sure, but I think my piano was, in fact, designed for this kind of playing.
It's a Yamaha T121 Professional Upright, and I practice on it 6 hours per day M-F, 4 hours per day on weekends.
Phil
It was, those are excellent workhorse uprights.
All this about broken bass strings makes me wonder about the quality of bass string manufacture nowadays; I put a Baldwin Hamilton upright through a practice regimen like yours in grad school and for many improvs a la quantum at that time and my dropout period. Never broke a string on that piano ( 30 years old now). I still use it for arranging/composing and late night practicing, I made a mute out of a cashmere scarf and that softens the blow. I don't think it's the blow that breaks the string though, it's the constant vibration that builds up when you play Scriabin Etudes and such for hours on end, day after day.
Which is what happened today on my Steinway "A". I've been practicing the Op.8 #12 for two months, and today was running through Pictures at an Exhibition and at the downward scale in Great Gate of Kiev was playing the last five notes FFFF when the low Eb exploded. That was scary ( but very cool

).
The Steinway's strings are 26 years old. When I first got that piano the strings were 78 years old, I used it intensively, about 6 hours a day 7 days a week for almost two years and the strings never broke. It was rebuilt while I was in college, I've had it for 10 years and it's seen constant use from me and my students ever since. This is the first string I've ever broken on one of my pianos.
Which makes me wonder what they're using for piano wire nowadays, scrap metal? Most of the worlds scrap steel ends up in Asia, and the pianos in question here are Japanese...
Have been surfing the net, looking for the right string to buy to replace the missing one and contacted the rebuilder, hopefully they still know what manufacturer made that set of strings. There's something called "Universal Replacement Bass Strings", which are evidently a one-size-fits-all/dougnut spare tire quick replacement option that tuner/techs can easily obtain, but are not good over long periods of time.