shape effect and structural stability

huangyhg

shape effect and structural stability
all thinkings, logical explanations are welcome and appreciated.
without edge support, a thin plate is unstable, unless a perfectly balanced (in direction of gravity) compressive load is applied.
the stability of the same plate is drastically improved once it is bent to shape, such as v, u, c, o, or curves, with or without the compressive force, why?

because a angle has a much higher crippling allowable
rb:
can you elaborate/stretch your response a little. seems it gets to the itching spot, but i still having difficulty comprehend/understand the phenomenon. thanks.
because you've drastically increased i, and, as a result, r.  this greatly increases stiffness in general, and compressive strength specifically.
structuraleit - good concise response.   
kslee,
your original summation ignores one thing, the plate is not perfectly straight. therefore the plate will still buckle under a perfect concentric load.