Published • Dr. Arnold Wilson, Dome Engineering Pioneer•
The Federal Emergency Management Agency has made literature available to communities that provides guidance and technical information, educating communities on how to become disaster resistant in the face of natural disasters (FEMA 2000).
James L. Witt, FEMA Director, has encouraged communities to follow FEMA guidelines: “Having personally seen the devastation caused by natural disasters, I am heartened to now see hundreds of communities commit to becoming disaster resistant through FEMA’s nationwide initiative, Project Impact. Project Impact operates on three simple principles: preventative actions must be decided at the local level; private sector participation is vital; and long-term efforts and investments in prevention measures are essential. The Federal Emergency Management Agency is committed to continue to develop tools, such as this manual, to help individuals, communities, states, and others create sustainable, disaster-resistant communities.
“When severe weather threatens, individuals and families need to have a safe place to go and time to get there. Thousands of safe rooms have been built based on FEMA designs, providing protection for families in their homes. Where will these people go if they are not at home? This manual provides specific guidance on how to provide effective shelter that can save lives when severe weather threatens away from home.”
Monolithic Domes meet FEMA requirements
The FEMA manual (FEMA, 2000) is a guidance manual for engineers, architects, building officials and prospective shelter owners. It presents important information about the design and construction of community shelters that provide protection during tornado and hurricane events.
After reviewing the FEMA requirements for a structure capable of providing a safe shelter for people in areas where hurricanes and tornadoes represent a real danger, the Monolithic Dome, because of its very nature, heads the list for economy and strength to resist extreme loads.
The reinforced, concrete, double-curve surface of a dome is extremely aerodynamic. Domes have been designed to resist winds of 400 mph. Because of the egg-shaped surface, the extreme winds can be resisted usually with only minor increases in materials and labor.
Conventional buildings have walls connected to foundations and to roofs with specially designed connectors, while a Monolithic Dome is continuously attached throughout with steel reinforcement greatly in excess of that required to resist extreme wind forces. Therefore, the Dome solves the safety issue by utilizing the entire structure to provide “near-absolute” protection.
When doors and windows are open on a conventional structure or when a rapid change in pressure creates large internal as well as external forces, the Monolithic Dome resists both of these conditions without special details of construction.
Wind-borne debris (missiles) often will perforate the envelope and other components of any conventional building. FEMA and others have investigated tornado damage and debris fields and concluded that a 15 pound 2″ × 4″ wood missile traveling 100 mph impact speed should be used for the missile impact resistance (p.3-14). They have shown that for a flat wall section a reinforced concrete wall, at least 6 in. thick reinforced with #4 rebar every 12 inches (both vertical and horizontal) has proven successful for missile speeds of 100+ mph. They have also shown that an insulating concrete form (ICF) flat wall section at least 4 inches thick reinforced with #4 rebar every 12 inches (both vertical and horizontal) was also successful for missile speeds of 100 mph (m.6-11).
For a Monolithic Concrete Dome that is prestressed in biaxial compression and double curved, representing the upper roof portion of a large dome and 3 to 4 inches thick with 3 inches of urethane foam insulation on the outside plus an outer covering of heavy nylon reinforced fabric , and reinforced with #3 rebar at 12 inches both ways, is also capable of resisting the 100 mph missile test. The testing that has been done to date represents flat walls with the missile hitting perpendicularly to the wall. The dome surface will resist greater forces in three ways:
The double curved surface is much more resistant than a flat surface; A biaxial pre-compressed wall will resist the impact loads much better than a non-compressed wall and impacting the sloping roof surface of a dome perpendicular to the surface would be rare occurrence meaning that a much smaller component of the force would be applied perpendicular to the surface most of the time. The thin shell reinforced Monolithic Dome has great resistance to flying debris.
I have personally engineered approximately 1400 Monolithic Domes in nearly every state and many foreign countries. Many domes have been subject to hurricane forces and a few to tornado forces. All have withstood these forces in an excellent manner.
I am convinced that a Monolithic Concrete Dome can be readily designed to meet all FEMA requirements for community shelters as well as home shelters. In fact, during the last few years several Monolithic Domes have been built per FEMA 361 and FEMA funded up to 75% as school/community tornado shelters. Many more are in the design process.
Note: In 2008, Dr. Wilson authored Practical Design of Concrete Shells, a technical book on thin-shell design, complete with formulas and programs. It’s available through Monolithic.
Reference: Design and Construction Guidance for Community Shelters, FEMA 361, July 2000
Note: Dr. Wilson wrote this article in February 2004. It was updated in 2011.