Originally Posted by
Rama
Can't say what caused it, but being a wrench we would open up the panels on the right side below the main deck floor so QC could do NDT testing.
Someone had told me it was because Boeing designed the aircraft to have some flex in it, but the door installations all the airframe stiffening led to the cracks.
One can see how a big door frame on one side might change the way the other side flexes, make it not symmetrical and induce some twisting.
You could probably solve that with some stiffeners in the shape of a door frame opposite the actual frame.
Modern computational analysis should be able to predict such potential issues.