NIST releases report on Katrina-Rita impacts on structures

Stricter adherence to existing building standards, model building codes and good building practices, and a greater recognition of the risks posed by storm surge, could minimize the kind of structural damage experienced in the Gulf Coast states hit by Hurricanes Katrina and Rita last year, says the Commerce Department's National Institute of Standards and Technology (NIST)in a new report.

The report documents the findings of a multi-organizational team - coordinated by NIST and made up of experts from private-sector, academic and federal entities - that deployed three subteams of technical experts in October 2005 to areas impacted by Hurricanes Katrina and Rita to conduct a broad-based reconnaissance on the performance of a variety of physical structures during the storms.

The reconnaissance was intended to identify new technical issues that need to be addressed in the rebuilding effort, in the improvement of building standards and model codes, and in future research studies - and to build upon knowledge gained from previous post-hurricane damage assessments.

The report makes 23 recommendations for specific improvements in the way that buildings, physical infrastructure (such as bridges and utilities) and residential structures are designed, constructed, maintained and operated in hurricane-prone regions across the United States - not just in the states affected by Katrina and Rita.

Federal agencies, state and local governments, and the private sector already have taken many actions consistent with NIST's recommendations to facilitate rebuilding and mitigate the potential for damage from future storms - in many cases even as the findings were being analyzed and recommendations were being formulated.

The NIST report urges state and local agencies to adopt and enforce building standards and model codes regarding hurricanes - and to make relatively straightforward changes in building practices. For example:

* Many roofing failures resulted from an inadequate number of fasteners being used in installation or fasteners being incorrectly located. NIST recommends that state and localities consider licensing of roofing contractors, continuing education of contractors and field inspection programs to monitor roofs under construction.

* Wind-borne gravel from building rooftops caused a great deal of damage to nearby structures. Model building codes do not permit this type of roofing in high-wind zones.

* Several buildings were rendered inoperable because critical equipment, such as electrical systems and backup electrical generators, were located at or below grade and damaged by floodwaters. Adoption and enforcement of existing model code provisions that require a building's critical equipment to be placed above potential flood levels could keep many buildings functioning following a hurricane or return them to normal use more quickly.

* Masonry wall failures observed during the reconnaissance may have been prevented had the walls been properly anchored and reinforced as required by model codes.

Several federal agencies already are acting on another area of improvement identified in the report: reviewing and updating flood hazard maps to better reflect the hazard due to storm surge, current velocity and wave action in the design of coastal structures - especially for the affected Gulf Coast regions.

Also being reviewed is the Saffir-Simpson Hurricane Scale's treatment of storm surge effects. The scale provides an expected storm-surge height associated with the intensity as determined by sustained wind speed. In the case of Hurricanes Katrina and Rita, the reconnaissance team found that storm surge heights at several locations exceeded those associated with a wind-speed based hurricane category. The National Oceanic and Atmospheric Administration (NOAA) bases its hurricane advisories on the results of detailed storm surge simulation models that account for the local topography and bathymetry (depth from the sea surface to the seafloor), as well as hurricane parameters such as size and track.

Additional recommendations in the NIST report cover the performance during hurricanes of bridges and parking garages; buildings (including pre-engineered metal buildings, moored casino barges, portable classrooms and manufactured homes); residential and building roofing systems; building envelopes such as window systems and exterior cladding (to prevent damage from wind, wind-borne debris and water-ingress); utility (electric, water and gas) systems; and seaports (wharves and large cargo cranes).

The NIST report's recommendations make clear what actions can be taken immediately to lessen or prevent hurricane damage to structures, and defines those actions that will require longer-term, greater effort. NIST believes that all of its recommendations are realistic, appropriate and achievable within a reasonable period of time.

•Date: 14th June 2006• Region: US • Type: Article •Topic: BC facilities and buildings
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