Volume 49, Issue 5 - May 2014

feature

Three Years Later
The Effects of the Joplin Tornado Live On
by Ellen Rogers

Cold, hard facts: “The failure of building envelopes at St. John’s Regional Medical Center (SJRMC) [in Joplin, Mo.], which led to loss of protection and subsequent extensive damage to building interiors … was the primary cause for the complete loss of functionality of this critical facility, which occurred despite the robust structural system that withstood the tornado without structural collapse.”

This information was reported in the National Institute of Standards and Technology’s (NIST) final report on its technical investigation into the impacts of the May 22, 2011, tornado that struck Joplin, Mo.

While the building exterior’s failure caused devastating destruction, the report also shines a positive light on certain glass products, noting, “The majority of the impact–resistant windows on the fifth floor (Behavioral Health Unit) of the West Tower of SJRMC remained intact, whereas most regular dual–pane insulated [sic] windows at SJRMC were broken when exposed to the same tornado hazards.”

The NIST Joplin tornado study was the first to study a tornado scientifically in terms of four key aspects: storm characteristics, building performance, human behavior and emergency communication—and then assess the impact of each on preventing injury or death. It also is the first to recommend that standards and model codes be adopted for better tornado-resistant buildings. In its recommendations, NIST calls for nationally accepted standards for building design and construction, public shelters and emergency communications that can significantly reduce deaths and the steep economic costs of property damage caused by the fiercest of storms.

Strong Standards
As part of its report, NIST also recommended that nationally accepted performance–based standards for the tornado–resistant design of buildings and infrastructure be developed and adopted in model codes and local regulations. These codes would enhance the resiliency of communities to tornado hazards. “The standards should encompass tornado hazard characterization, performance objectives, and evaluation tools. The standards shall require that critical buildings and infrastructure such as hospitals and emergency operations centers be designed to remain operational in the event of a tornado.”

The study points out that there currently are no standards for the tornado–resistant design of ordinary buildings and infrastructure, except for safety–related structures in nuclear power plants and storm shelters or safe rooms. The report notes that even they have inconsistencies in the way tornado hazards are characterized, as reflected in the different tornado regionalization and associated tornado design wind speeds for the contiguous United States.

According to the report, “performance–based standards for tornado–resistant design of ordinary buildings—including critical facilities, commercial and residential buildings—will result in more tornado–resilient communities … by explicitly considering tornado hazards, which will be characterized by the most up–to–date tornado data and risk–consistent science–based methodologies, as a structural design condition.”

NIST’s recommended standards would:

• Prescribe “tornado–prone areas” for design (i.e., regionalization of expected tornado windspeeds and wind–borne debris loading) based on a review of the most up–to–date tornado data and hazard mapping methodology;

• Specify “design tornadoes” for buildings (wind speed and debris impact loading) in accordance with the prescribed tornado–prone areas and based on buildings’ Risk Categories; and

• Specify “tornado performance objectives” for buildings, also based on buildings’ Risk Categories.

Design Measures
In its report, NIST also recommends the development of “risk–balanced, performance–based tornado designs methodologies such that all building components and systems meet or exceed the same performance objectives when subjected to tornado hazards.”

As NIST points out, there is currently no methodology for building design that specifically considers the design hazards associated with tornadoes. “The minimum code requirements for wind loading in current building codes do not take into account the inconsistent performance of different building components … when subjected to tornado hazards.” The report also cites the performance of building envelopes: “failure of building envelopes, despite the robust structural system that could withstand the tornado without structural collapse, often resulted in extensive damage to building interiors.”

Stay Safe
In addition, NIST found “inadequate performance among the best available refuge areas in the high–occupancy commercial BTS buildings that it surveyed.” As a result, it recommends that: “(a) a tornado shelter standard specific for existing buildings be developed and referenced in model building codes; and (b) tornado shelters be installed in new and existing multi–family residential buildings, mercantile buildings, schools and buildings with assembly occupancies located in tornado hazard …”

NIST will now work with the appropriate code development organizations to use the study’s recommendations to improve model building codes and lay the foundation for nationally accepted standards. NIST also will work with organizations representing state and local governments—including building officials—to encourage them to consider implementing its recommendations.

Ellen Rogers is the editor of USGlass magazine. Follow her on Twitter @USGlass and like USGlass on Facebook to receive updates.


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