I only recently found out that my research institution has a database for open access articles!
We can send in our previously published work, and they will check out all the copyright stuff. And then, the Digital Collection team can usually make it openly available online. AWESOME!
I thoroughly recommend seeing if your institution has a service like this too.
Just submitted my first article, previously published with Australian Centre for Geomechanics, on mine rehabilitation frameworks. You can look at it here.
Happy Open Accessing!