Monday, January 23, 2012

Tornadoes On The Beach During Katrina?

As part of my blog, I will take you into heart of Hurricane Katrina where we will look in detail at what structurally happened to a few beachfront properties on the Mississippi Coast. This detail tells a different story than what you might think happened. Here is my first installment of Hurricane Katrina on the Mississippi Gulf Coast.

I will never forget the remains of the first house that I studied that was destroyed by Katrina. At first it looked like everything had been put in a blender and just poured out. Nothing made any sense, but after studying the debris, I started to understand what I was seeing. This was a site that was covered with surge debris that had no relationship with the structure I was evaluating. I estimated that about 60-65% of the debris on the site came from somewhere else other than the site I was trying to evaluate. This had been a brick house in Waveland Mississippi and there was nothing left of the structure but some brick veneer, the slab, and a bird bath. There was some lumber and a roof truss sitting on the slab but these were things that floated in with the surge. The key was not the surge debris but the brick veneer and how the brick was displaced. All of that was under the surge debris. Then I realized that what I was looking at was superposition. A fundamental rule in geology that says that what is on the bottom happened first. All this debris--the lumber, the cars, the sinks, the roofing material, and the bricks, was now, from an analyst's perspective, material that could be studied just like a sedimentary deposit. In addition to superposition, there are other concepts that help show an investigative engineer what happened at a site. For instance, a chimney that just fell over looks totally different from a chimney that had been knocked down by flying debris, and since masonry does not float, it survives the surge and leaves a fingerprint of what really happened. By the time my investigations were completed, I had seen evidence that strong tornadoes had hit the Mississippi coast during Hurricane Katrina and before the surge. But according to the official record there were no tornadoes near the Mississippi coast associated with Katrina. The record shows there were 13 tornadoes on August 29, 2005, none stronger than an F1, all located in central Mississippi.

My job, as a damage investigator was very specific. I needed to determine if each structure was destroyed in part or in totality by wind or by water. This was necessary because specific insurance policies cover each type of damage. With such a daunting task I decided that the best chance for evaluating the demolished properties was to map the debris field from each structure. To my knowledge I am the only engineer that attempted this in the obliterated beachfront zone left by Katrina. For each property an enlarged aerial photo taken after the storm was printed and used on the site. Objects in the photo could then be related with the real objects on the ground. From this, along with field measurements, a scale and a site plan could be established. I worked with the property owners whenever possible, to identify debris that came from their property. Items like masonry that could not float got high priority but the study of wood framing that was anchored so that it could not float was also very beneficial. The tornado evidence I show here is limited, but there is much more and I will post it as I can find time to do so. I will start with one of the most remarkable items of debris that I saw on the Mississippi Coast. Of the eight demolished residences that I investigated from Waveland to the Biloxi Back Bay half had brick chimneys. In Gulfport Mississipi a four foot high segment of one chimney was found 230 feet from where it was built. Because this was not a bouyant item, it really caught my attention.

This story is about another chimney constructed near the northwest corner of a one story beachfront house in Pass Christian Mississippi. The house was located 20 miles west of the where the eye made landfall near the Mississippi-Louisiana border. Here the maximum peak wind gust was determined to be 144 mph using wind speed sensors that did not fail. The maximum sustained wind speed (ARA data) from the hurricane at this location was rated at 100 mph off shore and 90 mph inland.

This residence was estimated to be about 600 feet from the beach. The most remarkable thing about the chimney was it’s pristine condition. It looked as though it could have been lifted with a crane, patched at the top and reused, flashing and all. But it was lying 100 feet from it’s foundation in the driveway behind the house. This segment of the chimney broke off from the lower part just below the roof flashing. The lower part of the chimney was in 2 segments lying about 15 feet from the foundation. Each piece of debris in a hurricane has a history. That history includes forces that were applied to it while it was still attached, its dismemberment, its transportation to its resting place and anything that happened after. The story that this picture tells is that the roof blew off the house bending the flashing up on the south side of the chimney (the back side in the photo). The roof and contents from the house landed in the driveway then the chimney blew off and landed on that debris. The chimney impacted upside down on it’s top and fell over on the debris (without rolling) damaging only the top of the chimney. Later the storm surge cleaned everything from the site that would float away except for the roof deck and shingles that were pinned down by this chimney. The cleanly torn plywood roof deck is also a testament to the kind of forces that were involved. There was no other roofing material from the house found at the site. A 7 minute video of this chimney can been seen on YOUTUBE. The displacement of this chimney by 100 feet appears to indicate wind speeds exceeding the official wind records. Here are my thoughts behind that.

If we use the Enhanced Fujita Scale for guidance we must match our damage with a list of degree of damages (DOD) for residential construction. This scale then gives a range of wind speeds for each level. In this list, 1 is minimal and 10 is described as “destruction of engineered and/or well constructed residence; slab swept clean.” Level 6 is described as “Large sections of roof structure removed; most walls remain standing.” That sounds too low. I think we are at the level where all walls will be collapsed and that takes us up to level 9. At level 9 the wind speeds range from 142 to 198. At level 10 the maximum wind speeds go up to 220. This means that at level 9 at the bottom end we are just touching the maximum wind gusts reported for the area with Katrina. The problem is that I think it would be very unlikely that this chimney would detach and then travel 100 feet under a wind gust. To move this chimney I think we need a longer duration of wind. If that is correct then the sustained wind speeds (90-100) for Katrina alone are not high enough to create this damage. The damage description for these winds speeds is level 4; “uplift of roof deck and loss of significant roof covering (more than 20%);collapse of chimney..” This is a roof that most likely could be repaired if it were not for the higher wind gusts that very well could have destroyed the roof.

Because of the storm surge associated with strong hurricanes, the best way to evaluate wind speeds from damage, is in the storm related displacement of non-buoyant materials like masonry. Unfortunately, I can not find in the literature, debris field studies that include masonry transport from tornadoes. As a result I have started this line of research. There limits to what I can do in this regard, so outside field studies are badly needed. For starters how far does a segment of brick veneer travel during different wind speeds? And when chimneys are present what happens to them?

Friday, January 6, 2012

What is The Meaning of Science?

This blog will provide the background for most of my future blogs, so it may be helpful to read this first. I decided to start with the definition of science. All the different definitions I could find were considered, but my favorite published definition is in Wikipedia: "Science is a systematic enterprise that builds and organizes knowledge in the form of testable explanations and predictions about the universe." However, I can't get excited about the use of the word "enterprise" and science seems to be a very progressive sort of a thing, because nature has layers like an onion. The historical improvements of microscopes and telescopes has revealed the hidden layers of nature. So here is my improved definition:

Science is a systematic process that progressively builds and organizes knowledge in the form of testable explanations and predictions.

An added thought: science is the universe trying to understand itself.

I took the word enterprise out of the definition because that word makes it sound like science is something that is disconnected from ordinary people. Well, a lot times science is very enterprise like the Large Hadron Collider (LHC). But isn't science also a personal journey? I think every kid with a telescope or a microscope is also doing science. They may not be contributing to science (although they can) but they are beginning the process of learning how science is done. Every now and then science is done accidentally, but usually it is the result of committed individuals often doing hours of tedious work. The scientific process is progressive because previous discoveries leads to new discoveries. This is the real beauty of science. If science is wrong and it does happen, then the process stagnates. When that mistake is corrected, then a virtual explosion of new science is developed. My favorite all time wrong-turn in science, was the idea that the earth was the center of the universe. This idea persisted for some 1800 years after Aristarchus of Samos, circa 280 BC, correctly understood that the sun was the center of the known universe. The reversal of thought resulted in what is called the Copernican Revolution. I personally suspect that there are some wrong turns in science that are just beginning to slow down the natural progression. In engineering and physics there are always assumptions. This I think is where we often get in trouble. A good theory or even a good design process should always begin with a close look at the assumptions.

The theme for this blog is; assumptions in science that may be wrong!

The first wrong assumption I uncover is that, I think scientists incorrectly have assumed that news reports were false where meteors destroyed structures. In my blog, Historical Meteor Shockwave Events That Destroy Structures", (see link below) I interpret these events as being shockwave events often where people are killed. So instead of the fatality rate from all meteor events being near zero, I think it is one fatality every 4 1/2 years. This is from news reports that have not been disputed. In my study I found a couple of reports that were questioned, but they were events where no one was killed.

Here is an index of all my blogs starting with the most recent:


Biblical Accounts of Volcanoes with Tsunamis - PART I  The first account was written by King David in 2 Samuel.

The Origin of Hogwallows and Gilgai - PART II  The conclusion of this blog.

The Origin of Hogwallows and Gilgai - PART I 10/31/2013. This is a closer look at a theory I published in 1994 to explain these landforms. Included in this blog is a great photo of gilgai at ground level taken from Google street view in Waxahachie Texas.

Extreme Building Damage Caused by Yazoo Clay 8/3/2013. This looks like earthquake damage, but we have not had an earthquake in Jackson Mississippi. This is what expansive soils can do.

Historical Meteor Shockwave Events that Destroy Structures 5/27/2013. This includes an amazing story of a store that was destroyed by a meteor in Bellefontaine Mississippi in 1900. I accidentally may have uncovered the real worldwide fatality rate from all meteor events. You need to see the photos of damage to a house in Jakarta. These pictures were copyrighted so I provide links. 

Google Earth Posts Photos the Day of the Meteor at Chelyabinsk 4/16/2013. You can see the full roof collapse at the Chelyabinsk Zinc Plant for the first time. See the location of the crater the meteor made in the frozen Lake Chebarkul. I add an amazing street level photo right after the brick was blasted into the street. This is my most popular blog.

Designing and Repairing Foundations built on Yazoo Clay 1/27/2013 I dispel the most common myths about Yazoo clay. This blog shows what we are up against when we build on this expansive soil.  

Fireball Meteor seen in Mississippi and Alabama 9/20/2012. These meteors are once in a lifetime events. This looked like it was close but all the sightings indicate it was over 200 miles away in Alabama. Amazing!

Tornadoes on the Beach During Katrina? 1/6/2013. The closest official tornado to the beach was 70 miles north in Hattiesburg Mississippi. In this example there had to be higher winds than were recorded as part of this hurricane. This post has a UTUBE video I made at the site on the beach!