Here’s how bars get bent:

1. There is a misconception that an Olympic bar will bend
if the plates are loaded on a bar that is left on a narrow bench
press overnight. That’s highly unlikely. But it’s a rumor that I
hear time and again.
2. All the imported bars from China have a very low tensile
strength and lower yield strength. Their bars can be bent by
doing an explosive deep knee bend with 300 pounds and
reversing direction fast.
3. Bars made from American steel of 130,000 to 150,000
PSI will hold up on light floor exercises and bench pressing but
are usually bent by dropping them on the floor or on the
power rack. And this is often the fault of the power rack design
as much as it is of the strength of the bar.
4. Another common way to bend a bar is to do bench
squats, which are deep knee bends stopping when the buttocks
touches the bench. The bending occurs when you can’t finish
the last repetition and get stuck in the bottom position with no
alternative but to throw the bar off your shoulders. The loaded
bar will drop three to four feet before hitting the nine inch
wide bench in the center of the bar. This will “take out” all but
the best bars, and it does not do the bench any good either.
5. Bars rarely bend from dropping when the plates hit first.
It almost always happens when the bar hits first, such as on a
power rack. This makes me wonder why, with all the great
designers around, none of the gym equipment manufacturers
can design and manufacture a shock absorbing power rack, or
a power rack designed so that if a loaded bar drops, the plates
hit first.