PGC International Annual Symposium Focuses on Mitigating Natural DisastersNovember 1st, 2011 by DWM Magazine
Experts from various government and private agencies talked about hurricanes, tornados, earthquakes and how best to fight natural disasters during the Protective Glazing Council International’s annual symposium on October 26 at the National Institute of Standards (NIST) in Gaithersburg, Md.
“Natural and technological disasters cause [the U.S.] an estimated $57 billion in damages each year,” said Stephen A. Cauffman, deputy chief of Materials and Structural Systems at NIST. He went on to explain how codes are designed to protect buildings. “The problem is that the link between basic research and building codes, standards and practices is weak. Science lacks [the measurements] to predict structural performance to failure under extreme loading conditions. It also cannot assess and evaluate the ability of existing structures to withstand extreme load, or design new buildings and retrofits using cost-effective, performance-based methods.”
Disaster resistance of structures is determined by building codes/standards and practices used when the structures were built, Cauffman said. “Most are highly prescriptive, simplified and inconsistent with respect to risk,” he said. “Codes and standards are developed by private sector organizations that often lack resources needed to develop technical bases to improve them.”
During Hurricane Katrina – responsible for an estimated economic loss of $70 billion to $130 billion – major buildings suffered wind-induced damage to glazing as a result of debris from aggregate surface roofs on adjacent buildings, damaged equipment screens on top of buildings and damaged facades or structure of adjacent buildings. “In many cases, buildings that suffered structural damage were built before current model building codes were available,” Cauffman said. “Design wind speeds in current codes and standards provide a sufficient level of safety if provisions are properly implemented and enforced.”
Detailed studies have to be conducted to identify mechanisms for water ingress into buildings during hurricanes, and improved building envelope construction and cladding systems have to be developed to resist water ingress, Cauffman said. “Moving forward, we will need risk consistent, performance-based codes and standards for resilience, and a comprehensive approach to design guidance for the built environment.”
In his presentation, “Testing for Tornadoes and its Influence on Codes,” Larry J. Tanner, P.E., of Texas Tech University said, “Seventy percent of insurance dollars [in the U.S.] go to storm-related damages; another 25 percent goes to earthquake damages.” In his experience, he said that during a storm, the glass that stay in are the inner lites of double-glazed windows. “That’s not saying that double-glazed panes are tornado-proof, but they do seem to provide some semblance of holding up,” he said.
The ASCE 7-10 has undergone significant changes to its wind load provisions, Tanner added. “The ASCE 7-10 wind-borne debris region is different for risk category II and some III and all of IV,” he said. “For category II, debris region is approximately consistent with ASCE 7-05, but there is significant reduction in distance from coast around Jacksonville, Fla., Florida Panhandle and North Carolina.”
Dan Kelley, group leader for Risk Management and Mitigation, Applied Research Associates Inc., headquartered in Albuquerque, N.M., talked about the “Coastal Retrofit Mississippi” residential wind hazard mitigation grant program. The Federal Emergency Management Agency (FEMA) formed the program right after Katrina, he said, with $29.3 million in total funding, and it retrofitted 2,000 homes in the three coastal counties of Mississippi. “It was 75 percent FEMA match and 25 percent homeowner,” he said. “Mississippi Emergency Management Agency was the grantee and the Mississippi Department of Finance and Administration was the sub-grantee.”
Errol Bull, P.E., with Momentive Performance Materials in Waterford, N.Y., presented on “Sealants in Glazing Systems for Earthquake.” Designers can either choose structural silicone glazing (SSG) or a dry-glazed system, he said. “The ASTM C1401-09a Standard Guide for Structural Sealant Glazing suggests that there are potential intrinsic benefits to using SSG systems in seismic regions, such as controlling and, in some cases, eliminating breakage normally experienced during a small to moderate earthquake,” he said. “SSG systems also minimize the opportunity for glass to impact the metal glazing pocket surfaces, eliminating a primary cause of breakage. And when a glass lite break does occur, the SGG system, due to continuous attachment of the glass edge, can retain much if not all of the broken glass, depending on glass type, and provided that the structural joint retains sufficient integrity.”