Ransome rebar

Early type of rebar invented by Ernest L. Ransome, an early proponent of reinforced concrete structures.

http://www.oldstructures.com/2015/01/21/ransome-bar/

https://en.wikipedia.org/wiki/Ernest_L._Ransome

This bar is usually indicative of a concrete structure being built prior to 1920.

Hammerquist Road Bridge (Pennington County, South Dakota)
Built 1916
Concrete arch bridge over Rapid Creek on Hammerquist Road
Open to traffic