As the majority of the planning had been done the night before, the team hit the ground running today. The team split into three groups and each chose transects out of the twelve that had been picked out to be done. Much in the same way as was done for the Tuscaloosa tornado, transects were chosen that cut perpendicularly across the path of the tornado. As the teams walked the transects, photos and notes were taken of each structure and structures of special interest were subjected to more intense inspection in the form of case studies.
In the morning, Dr. David O. Prevatt, John Miller and Bill Coulbourne met with field personnel from FEMA, the engineer for the City to get access to damaged areas and with Mr. Scott Cope, Building Official and Code Enforcement Supervisor for the City of Joplin, to discuss the damage and future possibilities for improvements.
Overall the damage so far has been similar to that found in Tuscaloosa, AL a month ago. However, there is a wider swath of damage but with fewer tree damage to houses. In the center of the path we observed numerous trees that had their barks stripped off indicating the very high wind speeds. There was also a greater variety in residential structures with a large proportion being older structures (>20 or 30 years) and most of them being of light-framed wood structures. Most residential structures did not have vertical load paths to resist uplift, i.e. we saw many houses with toe-nailed connections between roof framing and wall and nailed connections from the wood floor plate into foundations. While there were some homes with full-basements most had crawl spaces constructed by placing the floor framing on stone/rubble masonry or ungrouted unreinforced concrete stem walls. We did not see any reinforcing bars in foundations. Our investigation also revealed that structures (even relatively new ones) had experienced accelerated deterioration as a result of water damage resulting from long-term leaks at windows and doors to the wall sheathing. Further, in older homes we saw deteriorated wood along the ground floor which likely weakened its strength. Common failures included gable-end wall failures, uplift and displacement of whole houses and broken brick chimneys that crashed through wood roofs. The team also investigated failures of some engineered structures. Metal buildings performed particularly poorly in this event. Almost all metal (light industrial warehouses) in the industrial area off Katherine Street were destroyed. The resilience of the Joplin population is very evident as just a week after this tornado, clearing of debris, new construction and repairs are proceeding in earnest. In terms of specific structures, several were of particular interest in the transects we crossed today and are shown in pictures below.
Here the tornado had ripped off the metal roof decking and it appears that when it was destroyed, much of the lateral bracing for the wall went with it and as a result the wall collapsed inward, taking two trusses with it. Fortunately, no one was using the structure as a safe room and no lives were lost here.
Several failure modes here, including flexure and torque, indicate the wind forces possibly swung the top of the tower around in a circular motion before it finally fell in the NW direction directly on some nearby apartments.
Hurricane ties places every third or 4th truss weren’t enough to hold the roof on this apartment building, built in 1998, in place. This newer structure, while displaying some construction details from more recent building codes, it still lacked a continuous load path. There was no evidence of a mechanical tie to hold the brick wall cladding in place and there were very few brick ties observed.