When selecting storefront, curtainwall, entrances and other aluminum-framed fenestration, architects consider the advantages of daylighting, views and energy efficiency for every project. Going beyond thermal performance, hurricane impact-resistant and blast hazard-mitigation systems take design considerations to the next level. Protecting people is the first goal in designing building envelope systems.
Ensuring critical performance of hurricane and blast fenestration systems
Houston Methodist Baytown Hospital in Texas features Tubelite ForceFront Storm hurricane impact-resistant curtainwall, storefront and entrance systems. (Photo by Brian Austin Photography, Courtesy of Tubelite Inc.)
After an explosion in Nashville on Dec. 25, 2020, photos and video showed fenestration systems with glass blown out and debris pouring from the openings. More than 30 buildings required major repairs and renovations, with rebuilding expected to take more than 12 months.
Hurricane Ida made landfall in Louisiana on Aug. 26, 2021, and continued its destructive path up to New York. The Category 4 hurricane produced sustained winds reaching 150 mph and damage resulting in 30 confirmed deaths and up to $95 billion in economic costs.
The toll these man-made and natural disasters takes is visible in the devasted properties. Working closely with fenestration manufacturers, architects can provide project-specific performance requirements to ensure the criteria is met to minimize risk to their most valued assets, the occupants.
Design loads for blast mitigation are much higher than for hurricane impact-resistance; however, blast loads are very short in duration, whereas the effects of high-velocity winds and flying debris associated with hurricanes can last for many hours.
While similar to standard commercial fenestration, protective glazing systems are considered complete assemblies, including the frames, safety glass, sealants and connections. A critical design factor is glass bite—the amount the glazing that is captured within the frame. Increasing the glass bite helps ensure the glass remains in the frame during a catastrophic event.
For example, impact-resistant storefront frames’ typical dimensions are 2.5 by 5 inches compared to standard non-impact storefront frames’ typical dimensions of 2 by 4.5 inches. The larger frame allows additional glass bite and can accommodate laminated glass. Impact-resistant curtainwall systems have similar dimensions compared to standard components but are designed to accept laminated glass.
Manufacturers will have different limitations on mullion spacing, frame and glass size allowances. Depending on design loads, heavy wall mullions and internal steel reinforcing maybe required. Projects with high blast loads could require custom internal components, such as heavy-duty shear blocks and fasteners. In addition, up to four times the number of perimeter anchors may be required to brace the framing to the surrounding building structure. To determine the optimal fenestration system, architects, glazing contractors and manufacturers should collaborate and evaluate the following information.
Hurricane impact-resistant project
- Location—to determine whether it is in a wind-borne debris zone and which building codes have been adopted by the authority having jurisdiction. For example:
- By Florida state law, building envelope components—including windows, storefront, curtainwall and doors—are required to have Florida Product Approval for use in accordance with the Florida Building Code standards. Florida product approvals can be used in Miami-Dade and Broward Counties if the product listing includes High Velocity Hurricane Zone (HVHZ) endorsement.
- Projects located in Texas designated catastrophe areas seeking insurance coverage must use products evaluated by the Texas Department of Insurance (TDI) through its windstorm inspection program.
- Building type—for identifying the building’s or structure’s code-based Risk Category I-IV. For example, a hospital with surgery and emergency facilities is in the highest Risk Category IV.
- Design pressures—verify if ultimate or allowable stress design method was used to calculate design pressures for the fenestration
- Elevations—frame sizes and configurations
- Wall section—for determining anchor point locations
- Compliance—per manufacturer’s test reports
Blast hazard-mitigation project
- Charge weight and standoff distance
- Blast pressure and impulse
- Site-specific plans and/or civil drawings
- Elevations—for frame sizes and configurations
- Wall section—for determining anchor point locations
- Level of protection—as provided by the government agency. U.S. Department of Defense (DoD), General Service Administration (GSA), Veterans Affairs (VA) and other agencies reference ASTM F 1642-17 “Standard Test Method for Glazing and Glazing Systems Subject to Airblast Loadings.”
- Compliance—per manufacturer’s test report or project-specific blast calculations for the installed system by a qualified structural engineer As with all projects, carefully review the test reports and shop drawings to ensure the manufacturer’s system meets the specification requirements and the glazing contractor has everything necessary for a proper installation.
As Tubelite Inc.’s architectural sales consultant based in Florida, Kevin Haynes shares his expertise and more than 30 years of experience in helping architects evaluate, select and specify high-performance, aluminum-framed fenestration systems for commercial building envelopes. He can be reached at khaynews@tubeliteinc.com.