The following essay is reprinted with permission from The Conversation, an online publication covering the latest research.
Engineers are creating some of the strongest hurricane winds ever to hit land in a Miami hangar. These Category 5 winds can severify test buildings in a flash.
But they aren’t strong enough to keep pace with nature.
The facility was designed to test structures’ ability to withstand winds up to 160 miles per hour (257 kilometers per hour). Now, we’re seeing the likes of Hurricane Dorian, which shredded neighborhoods in the Bahamas with 184 mph (296 km/h) winds in 2019, and Hurricane Patricia, with winds clocked at 215 mph (346 km/h) off the coast of Mexico in 2015.
Studies show tropical storms are ramping up in intensity as the climate changes and ocean and air temperatures rise. Future storms like Dorian could require new testing facilities, which will be far beyond what is possible today. These facilities will be needed to design homes and infrastructure that can withstand them.
The Wall of Wind
Currently, there is only one U.S. university that can generate Category 5 winds, the strongest level of hurricane. This is the Wall of Wind .
At one end of the facility is a curved wall of 12 giant fans, each as tall as an average person. Working together, they can simulate a 160 mph hurricane. Water jets simulate wind-driven rain. The building at the opposite end opens up to a large field that engineers can use to see where structures fail and what debris flies.
The powerful tempests we create here allow engineers and others to examine weaknesses in construction and design, track and trace failures through buildings, and test new solutions in close-to-real-world storm conditions. Cameras and sensors record every millisecond that buildings, roofing materials, and other items fall apart or fail.
Ten years of research here have helped builders and designers reduce the risk of damage. That’s helpful when forecasters warn, as they do for 2022, of a busy hurricane season with several major hurricanes.
Lessons from hurricane testing
We’ve found in destructive testing that a structure will often rip apart in less than a second. It takes only the wind to penetrate the weakest point.
When Hurricane Dorian hit the Bahamas, many less-well-constructed homes turned into shrapnel, creating another problem. Even nearby homes that are built to withstand higher winds can be damaged if a building falls. Our testing has shown how debris from one building, under continuous winds of 130-140 mph or more, can take out the next building, and then that takes out the next building.
Roofs are often the weakest link. A roof is subjected to uplift force during a storm, so wind hitting the surface of the building needs to be able to escape. Wind can cause damage if it runs into objects in its path.
New designs improve how buildings resist extreme winds. For example, storms can create powerful vortices – winds that swirl almost like a corkscrew at a building’s edge – that can strip away roofing material and eventually lift the roof itself. One innovation uses a horizontal wind turbine along the edge of a roof to diffuse the wind and generate power at the same time, a double benefit.
Buildings can create weaknesses or deflect wind. Modern high-rises are designed to avoid sharp corners. Testing shows that more trapezoidal or rounded edges can reduce wind pressures on buildings.
Safety doesn’t have to cost a lot. One experiment showed how just US$250 in upgrades was the difference between a small, shed-size building standing up to a Category 3 storm – or not. Hurricane straps attach a roof truss to the perimeter of the house. Ring shank nails, which have threads around the shank to grasp the wood, can resist wind forces better than smooth nails. Hurricane shutters also block entry points where the wind can penetrate and trigger catastrophic failure.
Installation is also important. This explains why roofs that seem to meet building code requirements may still fail and fly in hurricanes.
Experiments we conducted have shown how an edge system – the metal elements between walls and the roof – that is installed just half an inch too high or low can prematurely fail at low winds, even though the system was designed to withstand a Category 5 hurricane. Roofers installing asphalt shingles and roofing tiles may need to go beyond the current code when sealing edges to keep them from failing in a storm.
Expanding testing: 200 mph winds storm surge
While engineers have been gaining knowledge through testing, the nature of storms is changing as the planet warms.
Warmer temperatures – fueled by increasing greenhouse gas emissions from human activities – enable the air to hold more moisture, and warmer oceans provide more energy to fuel hurricanes. Research shows that bigger and more intense storms that are heavier with water and moving more slowly are going to hammer the areas they hit with more wind, storm surge, flooding and debris.
One study estimated that if Hurricane Ike, which devastated Galveston, Texas, in 2008, were to hit in the warmer climate expected in the late 21st century, its winds would be 13% stronger and it would move 17% slower and be 34% wetter.
Storms like these are why we’re working with eight other universities to design a new facility to test construction against 200 mph winds (322 km/h), with a water basin to test the impact of storm surge up to 20 feet (6 meters) high plus waves.
Computers are able to model the results but they still need to be validated by physical experiments. Combining wind, storm surge and wave action will allow us to see the whole hurricane and how each component interacts to affect people and the built environment.
Disaster Testing is about finding ways to make homes more secure. However, homeowners must be aware of the weaknesses in their structures. For most people, their home represents their most valuable asset.