Dec. 28, 1879: Tay Bridge Collapses, Alas

They say that wind was discounted, and yet, I remember a BBC program about the disaster (it would have been before 1966, when I came to the States) where they quoted correspondence to the Astronomer Royal requesting wind speed information for the location, he replied 10psf with gusts to 40psf. The Engineer didn't change his wind calc when he lengthened the spans.

"psf"? "Per Square Foot"? I don't see anything remotely applicable at http://en.wikipedia.org/wiki/PFS; at http://www.acronymattic.com/PFS.html, I see the "Piper Fatigue Scale" (which turns out to be a means to assess fatigue in postpolio patients) and "Physical Functioning Scale" (tests older adults with a 2-minute walk): should this be "fps" for "Feet Per Second"?

ppf = pounds per square foot.

Sorry, I should have spelled it out, in my structural engineering world, it is used constantly. I forgot that I was "away from home".

pounds/square foot is correct.

p.s. If you had searched for 40psf, you would have had a better result.

Google "psf vs. wind speed" (including quotes), and the [apparently kinky!] results probably don't match either your structural engineering world, nor my mechanical engineering / physics one. A chart at http://www.nctlinc.com/velocity-chart/ appears to translate psf as inches of water (huh?). The Emswiler formula translates 10 and 40 psf as just over 63 mph [miles per hour] and 126 mph, respectively. For those who live where there is a SYSTEM of measurement, that's roughly 103 kph [kilometers per hour] and 207 kph, respectively.

The problem with that is that the comparison values for flat plate drag and wind velocity from that date were incorrect, as the Wright Brothers learned a little over 20 years later; we'd need to know what means the Astronomer Royal used to obtain those values, and correct for the error. Should be a fair first approximation, though.

Your search must be different than mine, on the first page of results:

WindLoadsP , Wind pressure (Psf), = .00256 x V^2 (V= wind speed in Mph). Cd , Drag coefficient, = 2.0 for flat plates. For a long cylinder (like most antenna tubes), Cd = 1.2. ...http://www.arraysolutions.com/Products/windloads.htm

And:

Online Conversion - Convert windspeed to force per areaI need to be able to convert wind speed of miles per hour or Km/hour to a force per ... Example what is the equivalent PSF of a 100mph wind? ...http://www.onlineconversion.com/forum/forum_1102108190.htm