ARA Research Examines Blast-Designed Buildings’ Stability in
By Dan Kelly
Hurricanes Katrina, Rita and Wilma devastated large areas of the Gulf Coast last year. The federal agency that is the landlord of federal facilities—the General Services Administration (GSA)—had several facilities that suffered damage from these storms.
Some of the damage was extreme, with a few buildings still not occupied more than one year later. However, two recently constructed facilities stood out not only as solid performers within the GSA building inventory, but also fared well when compared to similar nearby non-GSA buildings:
- The Dan M. Russell Federal Building and Courthouse in Gulfport, Miss., completed in 2003 (see related story in the October 2004 USGlass, page 86); and
- The Wilkie D. Ferguson Courthouse in Miami, which was scheduled to begin occupancy in August 2006.
These buildings were built with blast-resistant features that also were found beneficial in reducing hurricane damages.
GSA Design Criteria
The GSA now incorporates the Interagency Security Committee (ISC) Security Design Criteria into the design of most federal facilities. A component of the ISC Security Design Criteria includes hardening of the walls, roofs and window systems to mitigate the damage to a building and limit injury of the occupants in the event of an explosion.
The GSA wanted to know how effective a recently constructed facility, designed to meet the ISC Security Design Criteria for a medium-level of protection, would be against extreme weather conditions. Our company, Applied Research Associates Inc. (ARA) of Vicksburg, Miss., was contracted by the GSA to conduct an investigation of hurricane damage and financial loss for the U.S. Federal Courthouse in Gulfport, Miss. The research sought to evaluate the performance of the building’s window, door and roof systems when exposed to an extreme weather event.
While blast resistance and hurricane resistance typically are addressed separately in design, this study was conducted in order to learn how a building designed to meet blast requirements of the ISC Security Design Criteria would perform when subjected to extreme wind loads. One goal of the study was to investigate whether the blast and hurricane requirements could be integrated into an efficient, comprehensive building standard, which would ultimately save the government money while preserving building assets and, more importantly, lives and livelihoods.
The blast-designed windows in the Dan M. Russell Jr. Courthouse performed well when exposed to the extreme weather conditions of Hurricane Katrina. Similar building types in the immediate vicinity and across the Gulf Coast suffered significantly more extensive window damage. The extreme wind experienced during the storm damaged portions of the roof and roof-mounted HVAC systems, as well as a penthouse wall. Window damage was limited to several broken exterior lites of insulating glass units with no complete failure of the interior lites.
Financial Loss Modeling
To gain an understanding of the potential economic benefits of blast-resistant glazing on buildings in hurricane-prone regions, ARA’s HurDam and HurLoss models were used to evaluate the performance of the windows in the U.S. Courthouse in Gulfport for both a single event (Hurricane Katrina) and a 20,000-year ensemble of simulated potential events. Estimates of damage and financial loss were provided for four window design scenarios:
- Case A: As-built blast-resistant windows;
- Case B: Hurricane windows (Miami-Dade);
- Case C: Southern Building Code (SBC) 1999 windows; and
- Case D: Pre-code windows.
ARA’s HurDam and HurLoss models were able to predict quantifiable comparisons of damage and financial loss of the four window systems that were evaluated. The “as-built” blast-resistant design and Miami-Dade “hurricane” design both fared well in the damage and loss estimate models of Katrina, with estimated losses of 1-2 percent of the initial construction costs. The models indicate that windows designed to the 1999 SBC or typical pre-code designs would perform poorly if exposed to the same extreme weather conditions. The modeled losses of the “as-built” and the “hurricane” windows for the Katrina storm set are both approximately 10 percent of initial construction costs less than the SBC 1999 window and approximately 31 percent less than a pre-code design.
For the 20,000-year stochastic storm set, the financial model predicts similar results for the “as-built” and “hurricane” windows with an average annual loss of approximately 0.5 percent of original building construction costs. The modeled average annual losses of the “as-built” and the “hurricane” windows for the stochastic storm set are both approximately 0.2 percent of initial construction costs less than the SBC 1999 window and approximately 0.8 percent less than a pre-code design.
Two buildings within close proximity to the aforementioned buildings suffered severe losses and supported the modeling prediction. These are the Hancock Bank Building in Gulfport and the Colonial Bank Centre in Miami. The Hancock Bank building is currently undergoing a complete renovation, and the Colonial Bank Centre also required extensive window repairs.
Based on these preliminary findings, building owners will realize modest savings from properly installed blast- or hurricane-designed window systems, and more refined models would help quantify additional savings. Buildings designed for blast and hurricane protection should also result in less downtime and disturbance of tenants due to extreme loadings from weather or terrorist events. Further investigation is progressing on the efficient integration of blast-resistant and hurricane-resistant designs.
Acknowledgements: Michael Hahn and Frank Lavelle, project leaders, Applied Research Associates Inc., and Steven C. Smith, CCM, AIA - General Services Agency, GSA
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