3 Foot Deep Concrete Floors, Overkill?

[IMBY]

I'm reading The Sky's the Limit by Steven Gaines, Passion and Property in Manhattan, and it touched on the famous Dakota Apartment Building on Central Park West opened in 1884, where John Lennon was killed outside the building in 1980.

In describing its construction, I wonder if they got it right in this book, as it seems too incredible to believe:

"built like the Pyramids, with floors 3 feet thick and load-bearing walls over 2 feet wide. It stood at 7 stories tall because that was all the weight its base could support."

OMG! Where, in the late 1880's did they get all that concrete? Overkill?

And today, what is the width of floors in modern concrete buildings?

I surmise, if there is a World War III, this building will survive! Anything!

[scalziand]

Early concrete was pretty crummy compared to the stuff we use today.

It's possible that the floors were lightened by the use of hollow tile arches, or waffling the slab, if the 3 ft depth is correct.

Modern reinforced concrete floor slabs can be as little as 8 inches thick.

[ardecila]

^ Yes and no. Without the aid of reinforcing steel, concrete has to be much thicker and/or use structural tricks like arches or corbels. In that sense, the steel makes it more efficient and cost-effective.

However, steel oxidizes and rusts whereas concrete does not. That rust can eventually compromise the concrete structure. Roman concrete structures, which did not use any steel reinforcement, have stood for thousands of years with zero maintenance and even neglect, while today's concrete structures that DO use steel have to be refurbished every 40-50 years.

[CCs77]

I really, really doubt those slabs are made of concrete. By the time that building was constructed, reinforced concrete construction was barely in an experimental stage, so it is pretty unlikely they used concrete there.

The most common material for building floors back then was wood, not even steel was still widely used. They may have used some form of tile vault, like a catalan vault, which could've made the slab thicker, but not uniformily thick, so it would have been 3ft thick in the lower part of the vault, but much thinner in the center. That if it was indeed 3 ft thick, but I doubt it. My guess is that it is a conventional wood floor, and not 3 ft thick, maybe that figure was including the ceiling.