Potential Changes to ICC 500 Could Mean Retesting of Impact Systems

Several proposed changes to ICC 500 Standard for the Design and Construction of Storm Shelters could be up for review this fall, including changes that could impact glazing
requirements. These proposals were outlined by UL building science group principal engineer Dave Stammen, who explained what’s in the current code and what could change.

THE CURRENT CODE

The 2014 edition specifies that the testing missile for tornado shelters be a 15-pound 2×4 and that the missile for a hurricane shelter be a 9-pound 2×4. Tornado missiles tested at 100 mph equal 5,012 foot pounds of impact energy compared to hurricane missiles
tested at 34 mph, which are equal to 350 foot pounds.

“That’s a drastic difference,” said Stammen, who added that shelters tested to tornado standards must undergo pressure and missile impact tests while hurricane shelters must undergo pressure, missile impact and cycling tests. Pressure and missile tests are allowed on separate units.

Missile impact testing is done per ASTM E1886-05. Single doors must pass three impacts while double doors must pass three impacts plus one on the center/mullion. For doors with glazing, an impact must be made on the center of the glass if the glass is equal to or less than 12 inches. If larger than 12 inches, the door is treated as a window.

For windows, two impacts must occur on the same lite of glass, one at the center and one at a corner. If the window has interior mullions then two additional impacts must be tested, though this can be done on a separate unit, one on the center mullion and one
at the mullion base.

The pass/fail criteria specifies that the missile cannot perforate the interior surface, there can be no dislodgement or disengagement, no spalling and after all impacts the permanent
deformation must be less than 3 inches.

PROPOSALS FOR 2020

Stammen explained several of the proposals are already approved for the public draft. The major proposal that impacts glazing would require that any changes to listed impact-protective systems, such as a change of glazing, require evaluation by the listing agency
or retesting of the entire assembly.

“This is important because if you want to put stronger glazing into an approved product it would typically comply, but just because it’s stronger doesn’t mean the product will pass, especially in minimum sizes. The glass could push the energy elsewhere and fail the unit,” said Stammen.

Another proposal would make the length requirements of missiles less stringent. The length of a tornado missile could be between 10 and 15 feet as long as it meets the weight criteria of 15 pounds. Hurricane missiles could be between 6 and 10 feet as long as the 9-pound requirement is met.

Stammen anticipates that a draft of the ICC 500-2020 standard will be available for a 30-day public review in November. He said the goal is to have the 2020 edition published by December 2020.

The presentation took place during a webinar hosted by the American Architectural Manufacturers Association.

New Guideline Addresses Exterior Glazing for Wind Vulnerabilities

As increasingly powerful hurricanes continue to make landfall in the U.S., causing extensive wind damage to critical facilities, the Federal Emergency Management Agency (FEMA) has developed FEMA P-2062: Guidelines for Wind Vulnerability Assessments of Existing Critical Facilities. The document provides guidelines for assessing the vulnerability of critical facilities, including glazing systems, to wind pressure, wind-borne debris and wind-driven rain. The goal is to mitigate vulnerabilities to wind damage to avoid loss and disruption of service. The guideline incorporates observations and lessons learned from recent and past hurricanes, current building code requirements and other historic high wind events.

According to FEMA, the results of an assessment can be used by building owners; design professionals; entities that award repair, reconstruction or mitigation grants; as well as state, local, tribal and territorial government agencies developing mitigation plans.

The guideline’s list of five common wind vulnerabilities includes glazing breakage from wind-borne debris generated by hurricanes or tornadoes. The guide includes the example of a hospital in Florida where wind-borne roof aggregate broke the glazing of an intensive care unit, requiring evacuation during Hurricane Charley in 2004.

FEMA’s guideline recommends that if significant vulnerabilities are identified, but there are not sufficient funds to mitigate all of them, then the assessment team should prioritize. It should first prioritize structural elements and exterior walls, including glass curtain-walls, which have the potential to fail or collapse during wind speeds of 90 mph peak gust or less. If a weak glass curtainwall is identified, FEMA recommends evacuating areas in its vicinity when winds above 60 mph peak gust are forecasted to minimize the risk of
injury and death.

ASSESSING EXTERIOR GLAZING

Section 5.2 of the guideline covers exterior glazing and shutters, including impact-resistant systems. To perform a proper assessment of these elements, FEMA’s guideline requires that an assessor have knowledge of industry standards, manufacturers, system designs and current building code requirements.

The section includes two types of assessments for glazed assemblies: level one and level two. Level one assessments of exterior glazing are nondestructive and include research,
information gathering and observations. For a level one assessment, an assessor should:
• Review project design and original construction submittal documents;
• Determine the age of the assemblies;
• Review repair and maintenance records to help determine the service history and condition of the assemblies, as well as reports of any performance-related issues;
• Research weather records and historical weather data for the area during the life of the building;
• Interview building occupants for reliable information about the service history of the building or any prior or current performance problems;
• Conduct a site inspection to determine through observation the condition of the assemblies, as well as to identify the type and treatment of the glass, including whether the
glass is laminated or insulating and the thickness of each lite;
• Document anchor type, size, location and condition;
• Determine the condition of sealants and weatherstripping to help predict
current air and water infiltration performance; and
• Check the interior finishes around windows and skylights for evidence
of water intrusion.

If the level one assessment was sufficient enough to predict an assembly’s current performance or compliance with design criteria then no further assessment is necessary, according to the FEMA guideline. It only recommends a level two assessment if the level one assessment revealed that the glazing system has several more years of useful service life and the building is located where the basic wind speed is greater than 120 mph; the level one assessment did not provide all information needed; or the assumptions drawn from the level one assessment need to be confirmed. Level two assessments can include field testing, destructive analysis and theoretical analysis. The guideline recommends that for a level two assessment an assessor should:

• Conduct field air and water infiltration tests to confirm current field performance, likely using ASTM E1105-00, Standard Test Method for Field Determination of Water Penetration of Installed Exterior Windows, Skylights, Doors, and Curtain Walls, by Uniform or Cyclic Static Air Pressure Difference. Personnel and agencies experienced with field air and water infiltration testing should be used;
• Remove or partially disassemble typical assemblies;
• Analyze anchors and fasteners, which can be a critical step in determining predicted assembly performance;
• Review anchor substrates; and
• Conduct theoretical engineering analysis to develop performance criteria for existing assemblies when data are not available otherwise.

AAMA Updates Comparative Analysis Procedure

The American Architectural Manufacturers Association (AAMA) announced an update to AAMA 2502-19, its standardized comparative analysis procedure for determining the structural integrity of door and window products.

The document, titled Comparative Analysis Procedure for Window and Door
Products, was last updated in 2007.

“New content in the 2019 version of this standard includes guidance for unit sizes smaller  and larger than those tested as well as deflection and stress limits established by industry limits established by industry standards,” said Kawneer manager of new product development Tanya Dolby, who chairs the Requirements for Mulled and Combination Window Assembly (AAMA 450/2502) Update Task Group.

“These key changes increase the applications where AAMA 2502-19 can be
utilized to support a larger range of unit sizes,” Dolby said.

Regions where the performance of exterior door and window size is documented to meet specific structural design pressure criteria will find AAMA 2502-19 especially useful.

For door and window manufacturers, the procedure provides a uniform approach for dealing with different code jurisdictions and specific design pressure for each size of fenestration product opening.

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