Archive for September 10th, 2008|Daily archive page

The Effect of Hurricane Winds Upon a House

Image courtesy of NOAA

Image courtesy of NOAA

What follows is an excerpt from a 1998 publication titled AMERICA’S HURRICANE THREAT under the auspices of the South Carolina Sea Grant Consortium.  What I’m showing you is a small part of their sobering account of what can happen to houses in the strong winds of a hurricane.  The house on the left in the image above is mildly damaged compared to many in that neighborhood.  I have been reading the above-mentioned report tonight due to my special interest in Hurricane Andrew.  Those of you who have been following this web-log since its beginning 18 days ago might recall having read somewhere that our home was a total loss in that 1992 hurricane.  In time, I have written about the experience in a recent posting dealing with window protection.  Here is the excerpt from the report:

“Andrew totally destroyed 63,000 homes and partly damaged another 110,000, making 250,000 people homeless. With roofs damaged or blown off, rain following the hurricane poured inside structures, soaking and collapsing Sheetrock and destroying billions of dollars worth of furniture, carpeting, televisions, and other items. The insurance industry estimates that 25-40% of insured losses were due to slipshod construction practices.

Most homeowners do not give a second thought to their roofs-until they leak or disappear. Yet roofs are the Achilles heel of homes in hurricane-prone areas from Maine to Texas.

As strong winds strike a building, their flow is diverted, swirling over and around the structure. Think of a mountain stream roaring against a giant boulder, which deflects the current. The stream flow accelerates around the obstacle, resulting in rapids. In the same way, hurricane winds speed up around corners and edges, creating suction that pulls on building materials like a super-powerful vacuum hose. Fierce gusts and suction pressure make a dangerous combination, especially for roofs. They yank off tiles and shingles, first at the roof edge and then along its slope as you’d peel an orange. During Andrew, huge numbers of tiles were stripped from roofs this way, and carried off by high winds, they crashed through windows by tens of thousands.

If you lose a window or door during a hurricane, you’re in big trouble. Extreme winds push through an opening in a building, increasing air pressure inside like blowing up a balloon beyond its capacity. If you force enough air pressure inside a house, it can break at its weakest point, usually the roof.

As roofs are being pushed off from within, they are being pried loose from the outside. Peel away tiles or shingles and you’ll find a covering of roofing paper, under which is plywood attached to rafters. But a roof won’t stand much of a chance in hurricane-force winds if builders haphazardly tie down plywood to rafters-if they use too few nails or miss the rafters altogether with their nail ‘guns.’ After Andrew, engineers reported that many contractors had routinely missed their marks. ‘With the use of automatic nail guns, the workman lost his feel for the nailing process,’ said Saffir. ‘The result was that many nails went through the sheathing into thin air, not into the truss or rafter below. This was a common occurrence.’

If your plywood sheeting flies away in the wind, you’ve lost more than just a roof covering. You’ve also lost a portion of the house’s structural integrity. That is, plywood sheets are often the sole lateral bracing for the rafters, actually holding the roof together. So with the plywood gone, the rafters are loosely tethered in the wind.

To compound the problem, many contractors fail to tightly fasten wood gable ends-the flat ends of a pitched roof-to walls. So when a powerful gust hits an unbraced gable, the gable end can be pulled loose at the wall, allowing wind to enter the building. If the roof sheathing is pulled off at the gable end, the rafters can fall over.

During hurricane Andrew, tens of thousands of homes were damaged due to such failures in roofs.”

NOTE FROM CLOUDMAN23:  Many of you reading this could be living in dwellings without adequate roof truss tie-downs and/or with poor roof sheathing attachment.  Do you know what the codes were when your house was built?  Do you feel confident that your dwelling was built according to code?  Were the inspections thorough and particular or were they inadequate?  For some, those are hard questions to answer.  In any event, please evacuate if Ike is heading your way.  Heed the warnings.  Please.

Please visit the rest of this web-log at https://cloudman23.wordpress.com/.  If you are interested in weather, there are some tutorials scattered about and more will be added in time.  At the end of this page there is a cue to click to the previous page or the next page.

LARGE HADRON PARTICLE ACCELERATOR FIRES UP

The large hadron particle accelerator at CERN fired up today for the first time.  Only running at “idle” it will likely give us insights into the world of subatomic particles that we haven’t yet considered even exist once they put the “foot to the floor.”  The huge device has a circumference of 27 kilometers (almost 17 miles) and when you study the image above you can barely see a hint of curvature.

If, like me, you learned in school that the atom’s nucleus consists of protons and neutrons and electrons might very well be outside the nucleus but associated with it – and that is still the model in your brain – wow – do I have news for you.

CERN is from the original name Conseil Européen pour la Recherche Nucléaire even though it is now called the European Organization for Nuclear Research.

If you are interested in learning about the world of particle physics today and the very large number of subatomic particles that have been identified, how they interact, and the forces involved, I highly recommend the book, The Dancing Wu Li Masters, “An Overview of the New Physics,” by Gary Zukav.  It is extremely well done and is written for people of all walks of life – not for scientists specifically.

LEFT CLICK ON IMAGE TO ENLARGE

Ike – Less Than 72 Hours Away From Texas?

CAUTION – THIS POST IS TIME SENSITIVE – THE TIME ESTIMATES AND GRAPHIC NO LONGER APPLY

Though the validity date stamp on late cycle spaghetti plots is not as recent as some available to you on line, it is my opinion that they provide a more accurate picture.  The following late cycle plot for Ike pretty much tells it all with regard to a Texas coast landfall.  I am inclined to place a high personal degree of confidence upon this.  However, hurricanes in the past have pulled some terrific surprises.  If you are anywhere else along the Gulf Coast, particularly other segments of the western margin of the Gulf and the western half of the northern Gulf coast – I would not let my guard down if I were you.  And, if you are, say, 50 miles inland, consider that at the nearest point, Baton Rouge is about 60 miles from the Gulf and over 100 miles from the Gulf along a line in the direction that Gustav moved.  Do a search and see what a mess they are in – right now. According to the “Advocate” newspaper today, there are still 57,775 residents without electricity.  And their winds were mainly tropical storm force though some gusts up to 91mph were reported.

If you are in harm’s way with Ike, I suggest you think in terms of evacuation.  As I understand it, evacuation directives have already been issued along some parts of the Texas coast.  Please read my September 8 post (just 2 days ago) titled “Window Protection For Hurricanes Essential.”  If it’s not on this page it will be on page 2.  At the apparent end of the post there is a place where you can click and read an account of my family’s experience in the aftermath of hurricane Andrew.  Read it and ask yourself if you want to try to ride out a big hurricane.  If you think life is stressful now – try adding the trauma of enduring the dangers of a strong hurricane and then, if you live, dealing with the high probability of post-traumatic issues.  I can think of nothing material worth trying to “protect” when a storm is in progress.  The time to protect “things” is before a storm.  It is still not too late to do some of that and then get the heck out of there.  You are far more important than any material thing.

“The Plot (below) is provided courtesy of Jonathan Vigh, Colorado State University. For more information about this graphic, click here.”

LEFT CLICK THE IMAGE TWICE FOR A LARGER VIEW