It is proposed to collect residential building damage data that is caused by the EF5 tornado in the city of Moore, Oklahoma on May 20, 2013. The damage path of this tornado overlaps the damage paths of two previous tornadoes of 1999 and 2003. It would be interesting to see how the houses reconstructed after the previous tornadoes perform in this tornado. Even though there are close to 1,000 tornadoes recorded each year, less than 10 tornadoes are rated EF 4 and EF 5. When an EF5 tornado impacts a city there is a unique opportunity to document building damage and learn from the damage. This tornado damaged two schools, several commercial buildings and more than 1200 residential structures. This project team will focus on documentation of residential structures. RAPID funding provides an opportunity to document the damage before damaged buildings are cleared and the debris is moved.
The project team will work with other RAPID grantee teams in the field to improve coverage of the damage area and avoid duplication. The team of faculty members and students will document failure modes, materials of construction, location of structures with respect to the center of the path, and debris impacts for documented structures. The institution is located within 20 miles of the damage area; this proximity of the documentation effort gives advantage of familiarity of the area. The RAPID team will develop contour maps of EF ratings and wind speeds based on observed Degrees of Damage. These maps will be compared with past tornado studies to evaluate the similarities and differences. This comparison will contribute to the understanding of the spatial characteristics of tornado wind forces on structures. Building failure progression will be determined in different wind speed zones. The benefits and challenges of using social media (twitters) to improve disaster assessment will be determined.
The Moore, Oklahoma Tornadoes provide a rare glimpse of an extreme tornado event (EF-5) occurring at the same relative geographical location twice in fourteen years. Evidence from the May 3rd 1999 and May 20th 2013 events were considered with a special emphasis on the lateral load bracing systems, structural progressive collapse mechanisms and the influence of building code requirements. The team focused on residential structures and the failures evidenced in these types of buildings. Residential homes built using the continuous sheathing method (R602.10.2 of the 2009 IRC) were compared to the intermittent bracing methods (Table R602.10.2 of the 2009 IRC) or the prior local codes (CABO 19995) which did not incorporate wind speed design parameters. On May 21st 2013 Dr. Ramseyer entered the tornado impacted area, while on May 26th 2013 the rest of the reconnaissance team arrived in Moore, Oklahoma. Along a series of transects perpendicular to the tornado's path, the team observed a dramatic change in the severity of damage from the center of the path towards the edges. These damage severity profiles were used to produce a damage severity contour map of the study area. In addition to mapping damage, in-depth studies were performed to leverage the technical data observed in the field. These studies include: the use and performance of storm shelters, performance of building materials and construction techniques, progressive failures of residential buildings, and how collected data can be used to improve laboratory simulations. In addition, a detailed aerial assessment of damage and debris was also conducted. Outcomes included: Residential structures in lower wind speed areas were examined and found to fail at garage door openings and at roof framing connections. A geolocation data methodology was developed and tested for use by extreme event damage assessment teams to collect, attribute, store, and distribute perishable damage data. Remotely sensed aerial imagery gave an understanding of flow and spreading of debris. Using aerial imagery from the May 20th 2013 tornado in Moore, it was observed that debris flow is typically manifested in thin "streak lines" spreading out from the direction of travel of the storm. By direct observation, high wind speeds at ground level were also noted. An analysis of residential storm shelter performance was conducted including above and below ground shelters. The results show that no inspected below ground shelters failed from perforation or penetration although in one case this type of shelter was flooded by severed water pipes and rain. And in some cases the exits were temporarily blocked by debris. One perforation, in an area of poorly consolidated concrete, was observed on an above ground ground insulated concrete form waffle-grid residential shelter. Two presentations at the national level and twenty two at the regional level have been given. Several web sites have been set up to disseminate information. A peer reviewed conference paper has also been published This research increases our understanding of progressive collapse of residential structures due to tornado wind forces. Tornado wind forces on a structure differ from those occurring due to hurricane winds in significant ways, we believe this is predominately due to the time duration of the events during their interaction with a structure. The difference of 5 minutes with a tornado versus 6 to 12 hours of high wind with a hurricane, impacting a structure. We have been able to show progressive collapse mechanisms that lead to residential structural failure. By improving the construction process, at a cost of between $1 and $2 per square foot, these collapse mechanisms can be improved to resist wind speeds up to 135 mph (IBC 2009 wind or roughly 150 mph IBC 2015 wind). This idea led Dr. Ramseyer and Dr. Holliday to develop the City of Moore Building Code for High Wind Events. It will help homes survive high wind tornado events up to 135 mph (IBC 2009 wind or roughly 150 mph IBC 2015 wind). This will protect this population from 95% of tornadoes considering that 97% of tornadoes between 2000 and 2011 were at EF2 or less. It will also protect a major portion of EF3, EF4 and EF5, considering that 80 to 85% of the damage area in the May 20th 2013 Moore tornado is at EF2 or less.
