Hello everyone. I hope y’all are doing well. I’ve been taking some time to plan my move to the new job and be as ready as possible for the new job. Today, I would like discuss the design of affordable DIY tornado shelters. For reference, I will use a rough description of a study performed by Research Engineer Bob Falk of Forest Products Laboratory in Madison, WI. (http://goo.gl/qRM87t)
Tornadoes have always been a risk for people living in the midwest; and as a result, the design of wind and debri resistant structures has always been part of the house construction conversation. There have been more technical and more resource intensive design/construction ideas discussed before. However, the reason I chose to do a blog post using this source is because the goal is a design that can resist 250 mph winds and debri using only affordable wood and construction methods. Additionally, the construction process is to be something that uses only basic construction skills. I really like this concept not because this is the perfect solution, but because this is good starting point for people to be reasonably safe. The design is constructed using interlocking timber with plywood overlay and the wood structure is connected to a concrete foundation using bolts. The door is still designed using steel; however, Falk is researching a way to use a wood door. The structure is currently undergoing testing using 2 x 4’s shot at 250 mph.
I believe that this would be a good design/construction process once the following issues have been addressed:
A repeatable design plan:
Whatever this design may entail, there needs to be an empirical, repeatable process that can be easily designed and built. A good plan should include the following at minimum: door frame requirements, bolt spacing requirements along the wall, nail spacing requirements along the plywood and interlocking timber sections, timber grading requirements, concrete foundation requirements, and roof connection requirements.
Design Study of the Door and Frame:
As far as wind is concerned, one critical issue is the door and the frame around the door. And especially after reading this article, it came to my attention because nothing is mentioned about the study of the frame. The design uses a steel door, so the door shouldn’t be the issue in that case. However, if the frame can’t resist the winds in the the hinge and bolt system and the wall/frame connection around the door the door system, it will fail to resist the loads. Some basic wind tunnel testing should be a good starting point.
Bolt Connection to the Foundation:
The walls shouldn’t be the critical part of the wall if this is constructed as it says. Yes, would splinters and could be dangerous; however, if the testing is occurring as described and enough strength is provided based on these studies the walls shouldn’t splinter. However, there will be some very high shear and moment loads on the bolts. If not adequately tested and designed, the wall could break of along the foundation. I would argue that this even more critical as well since it would affect a whole section of wall, so I believe details need to be examined here.
Roof Connection and Design:
With the increased wind, the uplift forces on this structure will be very high. Furthermore, I believe this has to be designed as an independent structure as well as a structure that is part of a larger building. With this in mind, uplift forces applied to the whole structure of the second floor or roof needs to be considered as well. Connections at the top of the wall need to be able to resist that full load or design needs to allow for relief of those forces if the house breaks around the shelter. Either way, study and wind tunnel tests are required for a safe design.
What is your opinion on the shelter mentioned in the article? Do you agree my assessment of the design? Is there anything I missed? Please share this post if you enjoyed it and have a good week!