Facts and thoughts relating to current tornado events.
A report from NOAA compiled the most dangerous places to be for the 2011 tornado season. Typically mobile homes account for the majority of fatalities, follow by permanent homes. But in 2011 permanent home accounted for the highest percentage of fatalities, with 43% of all fatalities occurring there. While this certainly illustrates the need for continued improvements to the current housing stock, it should be noted that the majority of impacted structures are permanent homes, so the fact that mobile home fatalities are so high illustrates even further the need for safer alternatives for current mobile home occupants. The original report can be accessed at http://www.nws.noaa.gov/os/hazstats/tornado11.pdf.
2011: Dangerous Locations during Tornadoes by Percentage of Fatalities
June 27, 2012
Tropical Storm Debby passed through the state of Florida during the morning of June 27th after impacting nearly the entire state for over four days with torrential rains, wind and tornadoes. Over twenty tornadoes were produced by TS Debby which damaged a number of properties and caused a fatality. A team of graduate students from the University of Florida that included David Roueche, Xinlai Penga and Ashlie Kerr traveled down to Lake Placid, FL early on the 27th to survey the damage caused by a tornado that occurred on June 24th. The survey found severe structural damage to three homes with minor damage to about fifteen others. Some of the worst damage included a two story home built in 1960 in which the top floor had most exterior and interior walls demolished and a home across the street which witnesses stated was completely destroyed. The debris was being cleaned up when the survey team arrived so the damages could not be confirmed. The poor construction quality of the home (no anchorage of the wood-frame walls to the CMU stem wall, built in 1972) and inspection of the debris appeared to validate the possibility of this damage description though. Using the specifications of the EF Scale, a Degree of Damage of 8 (most interior walls of top story collapsed) was evident in the two story home described previously, which suggests a wind speed in the range of 128 to 173mph. The poor construction quality of the home as well as the lack of damage to the homes on either side, would suggest a wind estimate towards the lower bound. A wind speed estimate of 130mph was chosen, which relates to an EF2.
Two-story home suffered DOD 8
Sheared Hurricane Tie on Boat House Behind Home
A home further along the tornado path was interesting in that although evidence suggested the tornado passed directly over or very close to the home, the only damage suffered was some sheathing loss. The home was built in 1981, but had been constructed to the South Florida Building Code which required hurricane ties at each roof-to-wall connection, anchor bolts tying the wood top plate to the reinforced CMU wall and a ridge vent along the entire ridge of the gabled home. If the tornado did indeed pass over the home, it is likely the enhanced structural design which limited the damage. The torrential rains which occurred after the sheathing loss however caused considerable damage to the interior of the home, illustrating how important a secondary water barrier could be in reducing economic losses. Analysis continues of the gathered data and more results will be posted as they are obtained.
May 22, 2012
Dr. Prevatt has been featured by author Pete Spotts in the weekly cover story of the May 14 issue of the Christian Science Monitor. The title of the article is “CSI Tornado: Decoding - and chasing - supercells with the experts”. The full article can be accessed here. In the article, Dr. Prevatt provides some of his observations from the Tuscaloosa and Joplin damage surveys, including the intriguing anecdotal evidence that many of the pre-1940 homes, built with diagonal planks instead of the thinner plywood sheathing, sustained less damage, even when shifted off of their foundation, than many post-1940s homes. The thicker planks and more dense nailing pattern required for this type of construction may have served to better hold the houses together even when the roof-to-wall or wall-to-foundation connections failed. Dr. Prevatt also states that providing tornado-resistant designs is “not as much of an engineering problem as it is a societal one, accepting what its risk is and what it’s willing to pay for its safety.” With the increasing economic losses from tornadoes and the increasing coverage of tornado damages, the society’s perception of their tornado risk may be changing, and we as engineers must be ready to provide the necessary solutions that society desires.
April 30, 2012
This past weekend marked the one-year anniversary of the devastating April 25-28, 2011 tornado outbreak. With over 500 tornado reports, nearly 200 of which were from April 27th alone, this four-day outbreak will go down in history as one of the worst US weather disasters. It caused 325 confirmed tornado-related deaths in six states, making it the fourth deadliest outbreak in US history. In addition, it was the costliest tornado outbreak in US history, causing an estimated $11 billion in economic losses. As we pause to remember this tragic reminder of nature’s power, our thoughts and prayers are certainly with the families of those who lost friends and loved ones, and those who even now may still be in the process of rebuilding their homes and lives in the aftermath. There is still much work to be done in the rebuilding efforts, and there is certainly much more work to be done in the scientific community to prevent such a disaster from happening again.
The results from our damage assessment of the EF4 Tuscaloosa, AL tornado once again highlighted facts that we in the scientific community have been told over and over again for more than a hundred years - our houses are inadequate to resist tornado loads and leave the residents extremely vulnerable to serious injury or death and loss of personal property. Even new homes are not being built properly to resist extreme winds and cannot be relied upon to provide adequate protection of life-safety or personal property during tornadoes. The same failure patterns that have been occurring for over a hundred years still occur today, an indication that innovative thinking and designs have not been extended to the residential sector. The question we must ask ourselves though as engineers is, if not now, when? When do we cease to accept that the loss of life and billions in property loss that occurs every year from tornadoes is unpreventable? When do start to view our housing stock not as individual, private sector investments, but instead as the valuable infrastructure that it is? When do we stop looking only at the problem and start looking for solutions? The fact that it is a difficult task does not make it any less necessary, and the experiences of the seismic community should illustrate that providing a solution to a difficult problem is possible if we begin to apply the innovative, problem-solving skills to this issue. Such disasters as these certainly provide the motivation but it is up to us as engineers and scientists to holistically view the problem and seek to identify plausible solutions.
It is exciting to see that some progress has been made even just in the past year. Workshops have been organized, in which Dr. Prevatt has actively participated, which have sought to integrate social, engineering and meteorological issues together to clearly identify the problems facing us and provide concise, achievable plans of action towards becoming a more weather-ready nation. Work continues to move forward in research as well, seeking to better understand the true nature of tornado loads on buildings. In January, 2012, Dr. Prevatt was awarded a CAREER Grant from the National Science Foundation in order to use his expertise and advanced knowledge of the load paths and structural response 0f wood-frame residential buildings to extreme loads to develop effective retrofits and design techniques for tornado-resistant homes. Changes will not be made overnight - it will take the full support of not only the scientific community but also of the residential communities, taking responsibility for the protection of their homes and livelihood. But with the upward trends in losses from natural losses, including tornadoes, the time is now to begin providing sustainable 21st century homes that are built to withstand the extreme storms that nature throws at them. It is our hope that the April 25-28th tornado outbreak will be not only remembered as one of the deadliest weather disasters but also as a turning point in the design of residential homes. A time when we as engineers, scientist and homeowners said enough is enough and demanded a more resilient alternative.
April 15, 2012
Continuing to follow developments relating to the latest round of severe thunderstorms and tornadoes. This is the second large outbreak of the year, the previous being the March 2-3 outbreak which predominately impacted regions within Indiana, Illinois and Kentucky. This newest outbreak has so far impacted Oklahoma and Kansas the most, two states within the region traditionally known as Tornado Alley. Over 98 tornadoes have been sighted according to preliminary SPC Storm Reports causing 5 confirmed fatalities. NWS officials are still in the process of assessing the damages but it appears Woodward, OK (Pop. 12,000), Wichita, KS (Pop. 382,000) and Thurman, IA (Pop. 250) were the hardest hit. Early reports indicated 75% of Thurman, IA was destroyed. Also in Iowa, the Greater Regional Medical Center in Creston was hit by a tornado, fortunately with no major injuries. Woodward, OK was previously hit by a devastating tornado in 1947 which caused 85 fatalities. This April 14th tornado has caused 4 confirmed fatalities and an unknown amount of damages. According to Mayor Roscoe Hill extensive damage occurred to a new residential area in the city.
No official information on the intensity of the tornadoes is available yet but several storm chaser reports cited large wedge tornadoes and indicated they may have been EF2 or EF3 tornadoes. Official estimates cannot be made however until damage assessments are made in accordance with the EF scale.
Tornado Damage in Thurman, IA (AP Photo/Nati Harnik)