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.

BNSF - Eagle Avenue Overpass (Carroll County, Iowa)
Built 1913
Concrete Slab Bridge over Eagle Avenue on BNSF Railway
Open

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