Historic Structural Detail: Thin Stairs

by Don Friedman on August 24, 2016

Fire stairs in a 1924 concrete-frame warehouse:


The brown paint is the edge of a concrete slab spanning from the right side of the landing on the right (above the lower door) to a wall out-of-frame off to the left. It’s four inches thick and spans about twelve feet; the treads are simply triangular extensions above, and integral with, the slab. This detail, including the specific locations and bends in rebar that are needed to make it work, were developed in the 1900s and 1910s and are still in use today on concrete stairs. I had a bit of nostalgia looking at this stair, as I designed my own version of it as a junior engineer in 1989, at the only skyscraper I’ve ever worked on* from early design through construction.

* I’m not sure if finding out that my only new-skyscraper project is the 53rd-tallest building in NYC is good or bad. I was on site shorty before the topping-out and it seemed quite high while I was standing on the bare formwork.

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