Tornado Storm Changes Requirements
Tornado loads sweeping through ASCE 7-22 design requirements! Roughly 1,200 tornadoes occur in the US each year. Given that tornadoes kill more people per year in the U.S. than hurricanes and earthquakes combined, ASCE 7-22 was revised to account for tornado loads. Understand how these changes could impact your next project.
Growing up in the northeast, tornadoes were these random events that occurred in the movies, and in far-off places like Kansas. But according to the National Institute of Standards and Technology (NIST), roughly 1,200 tornadoes occur in the US each year! AND they occur in all 50 states, but primarily in the lower 48 and east of the Rocky Mountains. Given that tornadoes kill more people per year in the U.S. than hurricanes and earthquakes combined, ASCE’s Structural Engineering Institute revised the ASCE 7 Standard for Minimum Design Loads and Associated Criteria for Buildings and Other Structures in hopes that it will be adopted into the 2024 International Building Code.
While it’s the right thing to do to save lives, the implications involved with designing a building to withstand the storm, like the catastrophic tornadoes we see on the news feels almost unattainable! ASCE created Chapter 32 to address the calculation of tornado loads. However, it is important to recognize that wind loads still must be calculated following the requirements in Chapter 30. Chapter 32 is required for Risk Category III and IV buildings only!
This covers essential facilities — such as hospitals and emergency response facilities — that need to remain operational in the event of extreme environmental loading. These buildings are required to maintain functionality after a design-level tornado. Where tornado loads control, design uplift pressures on the roof will typically increase. Code includes minimum design requirements. Enhanced design considerations, such as the requirements outlined in ASCE 7-22, are prudent and encouraged, regardless of Code adoption and mandates. After all, our main concern is to protect the health, safety, and welfare of the general public.
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