Here are a few I had already on photobucket. They're mostly related to my roof raise in which I disconnected the ribs from the chair rail instead of slicing them mid-span as is more commonly done, but anyway they do show the base connection.
In this latter picture there are 10 holes through the chair rail. There was a 1/4" solid rivet in each of them! Most of the ribs in my bus are secured with just four rivets, but those around the doors and those where the chair rail sections overlap (like shown here) used 6 additional rivets.
The ribs are probably roll formed for factory production, but I had some straight sections custom-made for my raise. I believe these were formed with a press brake. In the upper picture front and center a piece of factory channel is shown together with the extension I had made. The ribs on my bus have a U section inserted inside them, but most Blue Birds aren't this way. Most are open on the back like the extension piece is. I suspect it's because my bus was built for public transit and had windows about 60" wide rather than the usual 28" wide (?) used in school buses. Due to the wide windows, half the ribs don't connect to the floor and I think this is why they've reinforced those that do with this U channel insert.