Regarding Pittsburgh, there's absolutely a large working-class white contingent in sections of the city. This is the only city I've ever been too where there's a selection of what I can only call "white slum" areas. I mean,
this is a white neighborhood.
So is this.
So is this.
So is this. These areas do have growing black populations in some cases, and some of them are gentrifying, but they're all at least 50% white still - and got bad when they were 80%-90% white.
In terms of general city geography, working-class whites are on their way out almost everywhere, though they exist in such high numbers they're going to be a major factor in the city for a long time to come. It's hard these days to think of a working-class white neighborhood in the East End of the city at all, because this side of the city has been gentrifying rapidly over the last few decades. There are some pockets in the North Side however (where gentrification has mostly been limited to the historic brick rowhouse neighborhoods close to Downtown). The southern portion of the city (South of the Monongahela) is still overwhelmingly working-class white, with little gentrification/middle class presence outside of South Side Flats and pockets of Mount Washington, and only a handful of black neighborhoods.