CoconutCandy
(User)
Mon Jul 23 2007 11:43 PM
Wind Loading and the Saffir-Simpson Scale

Wow. This is all very interesting information. You've given me a lot to chew on. Thank you all for your replies.

First, a few relevant quotes:

>> How does the damage that hurricanes cause increase as a function of wind speed? The 148 mph hurricane (a category 4 on the Saffir-Simpson Scale) may produce - on average - up to 250 times the damage of a minimal category 1 hurricane!

>> TIME, another parameter to consider if you want to wrap your hands around damage potential ... These storms are very gusty. Time can be a factor.

>> No we do not want to get into your house vs. my house and how it was constructed...

>> In addition, the equation does not have an adjustment factor for strengthening or weakening hurricanes...

All these factors mentioned are certainly important in a 'real-world' scenario, but I guess my original thoughts were in a so-called 'idealized' environment.

Although the Saffir-Simpson Scale does qualitatively describe the kinds of damage that could be expected from each category, in addition to it's quantitative parameters, it doesn't answer, specifically, the 'Scale Factor' question I had proposed.

And yes, while the time factor is *certainly* a huge factor in the real world with any land falling hurricanes, (Charley vs. Jeanne), and the peculiar gustiness of tropical cyclones is also a real-world consideration, and even whether the storm is strengthening or weakening may play a role in the amount of destruction in any given area, what I am looking for an 'idealized' (purely mathematical) situation.

Here's my 'idealized' scenario: Wind velocity stays exactly the *same* for a given period (say, a 5 minute period), as in a wind tunnel experiment. The materials used in the construction of the 'test structure' are carefully determined and stays a constant for each of the 5 tests, for each of the 5 categories (min cat1, min cat2, ..., min cat 5). The size (square footage) of the exposed surface (perpendicular wall or sloped roof, etc.) is carefully taken into consideration and is an integral part of the equation.

Master Question: How much 'Wind Loading" (PSI per square foot per unit time, etc.) can be expected (measured) in this idealized scenario for each category of hurricane.

There must be some 'scale factor', as I mentioned in my above post that can be derived (determined) through carefully designed experimental procedures. Perhaps my proposed 'factor' of 5 might be on the high side, but it's pretty obvious it's not linear, and similar to an exponential scale, dramatically goes up as we get into a MAJOR hurricane, of Cat 3 and above.

I read this recently somewhere, so I think it's already been more or less worked out. Just forgot where I read it or what the proposed factor was.

But, on the flip side of the coin, you're all right: An idealized experiment doesn't help much if you're in a slow moving storm, in an older or weakly constructed building, the veering or backing directions of the wind as the storm passes by on the various parts (walls, roofs, etc.) of your house, orographic considerations, etc, etc.

These are all very important considerations for any one man in any one residence during the passage of any one hurricane. But there must be some 'pure science' at work here in an idealized world from which we can derive the sought after scale factor.

I've done a fair amount of research on google, and it appears the mathematics are quite complex and must take into account many complex variables. I didn't say this would be an easy question to answer.

Any additional thoughts, links, suggestions and the likes?



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