Originally Posted by slvoid
The top tube is in compression while the down tube is in tension.
Think about it this way, you roll a piece of paper up into a small tube, compress the tube, it withstands right? Now, dent it a little then compress again, it gets crushed.
Do the same and pull on it, dent it and pull on it again.
Don't you mean the down tube is in compression and top tube is in tension?