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# Guastavino Floors

## Guastavino Floors

(OP)
I am looking at a an early 1900's Guastavino vaulted floor and arch ribs. Guastavino wrote in his treatise that arch thrusts were calculated for the crown as H = LS/8r where L was the distributed uniform load, S was the arch span, and r was the rise from the arch spring to the crown. Kidder has the same formula in his construction handbook for that era. I'm puzzled on the derivation of this formula. If I take a freebody of half an arch, I come up with the thrust as H = LS^2/8r.

does anyone know how Guastavino and Kidder derived their formulas?

### RE: Guastavino Floors

I agree with you.  Could be typos?

### RE: Guastavino Floors

Just came to me.  L is the total load, not the load per length.  Try it that way, and you will agree with his formula.

### RE: Guastavino Floors

(OP)
You are indeed correct. A more careful reading while fully awake indicates that's what he meant for L.

I knew I would get a good answer here on Eng-Tips.

Thanks.

### RE: Guastavino Floors

Kinda reminds me of the chord force formula for plywood diaphragm - wl^2 /8B;

Isn't engineering wonderful!

Mike McCann
MMC Engineering
Motto:  KISS

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