At my elem. school we had a recess period to burn off energy between instruction sessions...playground activitywas essentially unsupervised with 2 or 3 teachers providing overwatch ( and some to sneak a cigarette) and wash cuts and scrapes with the dreaded but fascinating bubbling hydrogen peroxide. If you didn't have scabs on your elbows or knees, you weren't really having fun.
You mentioned yur concrete playground, we had a blacktop areaaround the back of the school with a much larger fenced off grass area, guess where we played most of the time.
I remember one like this but it was welded and the connections smooth. There was a pole (fire pole) in the center with a tiny platform on the top made from a grid of same sized pipe as the rest of the structure. I never gathered the nerve to climb on top and stand on the platform .