Broken frame rivets

Okey this is a picture showing the rear engine crossmember to the right and to the left is the crossmember slightly infront of the rear runningboard bracket. I assume this crossmember is meant to prevent the framerail from twisting when you step on the runningboard.
However just as I made everything ready for for shippment to media blast and paint I stepped on the rear runningboard frame bracket and noticed a small small flex between the crossmeber metal and the framrail. Like if the top rivet hole was slightly to large from years of stepping on the runningboards. I got a hold of a guy in my town that actually had all the toolings for pressing steel rivets. (Not very common is Sweden today). So of I went to the garage and grinden of the rivet heads. Then i tried to beat the rivet out with a sledgehammer and a punch. I was amazed on how firm it was to the hole not budging anything. So I took the pneumatic hammer and the same punch and after som heavy hammering it came out...... to my surprice, TWO pieces ended up on the floor. The rivet has sometime cracked into pieces from fatigue.  Really interesting to see the force needed to get it out despite it was cracked and one head was grinded off. 

Left side before grinding the head off.

Head gone

Two pieces, rust on the mating surface

Right side

Head is gone

Same same