One of my civil engineering professors at RPI used to always talk about the ‘built up’ columns in the New York City subway stations. The “I” beam shape is very strong and efficient, but it was impossible to make “I” beams directly before the 1908 when a man named Henry Grey invented a mill machine that could roll the shape. So steel workers needed to build their own “I” beams in the field by joining steel plates with rivets. I was reminded of my civil engineering studies when I visited Melk last week and used the pedestrian bridge to cross the tracks.
By the way, Grey worked for Bethlehem Steel, my first employer after graduating from RPI. I actually worked in one of the original “Grey” mill facilities in Bethlehem.