They are constructing the concrete arch approaches to the North Side Point Bridge (also known as the Manchester Bridge), completed 1915 and demolished 1970. The construction of the 2 Pratt Through Truss spans over the Allegheny River was substantially complete before the construction of the approach spans.

attached is a picture of the remains of the bridge pier from the end of the bridge closest to the camera in the image

The train trestle on the left was under construction at the time. Although it was destroyed some time ago, if you Google photos of Pittsburgh in the 1950s, you will see it was still in use then.

The bridge in left foreground has no approaches. Is it going up or coming down? Not present in the modern view posted by kozel. There doesn't seem to be any equipment or activity surrounding where the approaches should be.

[Like this? -tterrace]

The T.J. Keenan Building, previously seen here, still stands. It's hard to appreciate its beautiful red dome in a black-and-white photo.

This photo would have been taken from the top of the Duquesne Incline, one of the two surviving funiculars of more than 20 that existed at one time.