“Wind Wall” can blow up Category 5 hurricane force buildings

The following essay is reproduced with permission from The Conversation, an online publication covering the latest research.

In a Miami aircraft hangar, engineers recreate some of the strongest hurricane winds to ever hit land. These Category 5 winds can shatter a test building in the blink of an eye.

Yet they are not powerful enough to keep up with nature.

When engineers built the Wall of Wind test facility 10 years ago at Florida International University, it was inspired by Hurricane Andrew, a monstrous storm that devastated South Florida in 1992.

The facility was designed to test the structures ability to withstand winds of up to 160 miles per hour (257 kilometers per hour). Now we are seeing events like Hurricane Dorian, which tore through neighborhoods in the Bahamas with winds of 184 mph (296 km/h) in 2019, and Hurricane Patricia, with winds clocking in at 215 mph (346 km/h). km/h) off the coast of Mexico in 2015.

Studies show that tropical storms increase in intensity as the climate changes and the temperature of the oceans and air increases. Designing homes and infrastructure to withstand future storms like Dorian will require new testing facilities that go far beyond current capabilities – for what we believe should be called Category 6 storms.

The wind wall

There is currently only one full-scale test facility at a US university capable of generating Category 5 winds, currently the strongest hurricane level. This is the Wind Wall.

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. At the other end, the building opens up to a large field where engineers can see how and where structures fail and debris fly.

The powerful storms we create here allow us and other engineers to probe weaknesses in construction and design, track cascading failures in a building, and test innovative solutions under harsh conditions. storm close to the real world. Cameras and sensors capture every millisecond when buildings, roofing materials and other elements fall apart or, just as importantly, fail.

Ten years of research here has helped builders and designers reduce the risk of damage. This is useful when forecasters warn, as they do for 2022, of a busy hurricane season with multiple major hurricanes.

Lessons learned from hurricane testing

We have found in destructive testing that a structure often tears in less than a second. All it takes is for the wind to penetrate the weakest point.

When Hurricane Dorian hit the Bahamas, many less well-built homes were turned into shrapnel, creating another problem. Once a building fails, even nearby homes built to withstand stronger winds struggle from flying debris. Our tests have shown how debris from one building, in continuous winds of 130-140 mph or more, can destroy the next building and then the next building.

Rooftops are often that weak link. A roof is subject to an uplift force during a storm, so wind hitting the surface of the building must be able to escape. When the wind hits objects on this path, it can cause damage.

New designs improve building resistance to extreme winds. For example, storms can create powerful vortices — winds that swirl almost like a corkscrew around the edge of a building — that can strip roofing materials and possibly lift the roof itself. One innovation uses a horizontal wind turbine along the edge of a roof to diffuse the wind and generate electricity at the same time, a double benefit.

The shape of buildings can also create weaknesses or help deflect wind. You will notice that most modern skyscrapers avoid sharp corners. Tests show that more trapezoidal or rounded edges can reduce wind pressure on buildings.

And better security doesn’t have to be expensive. One experiment showed how just $250 in upgrades was the difference between a small hangar-sized building withstanding 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 grip the wood, can withstand wind forces better than plain nails. Hurricane shutters also block entry points where wind can enter and trigger a catastrophic failure.

Installation is also important and helps explain why roofs that appear to meet building code requirements can still fail and fly in hurricanes.

The experiments we conducted showed how an edging system – the metal elements between the walls and the roof – that is installed just a half inch too high or too low can fail prematurely in light winds, even if the system has been designed to withstand a Category 5 hurricane. Roofers installing asphalt shingles and tiles may need to go beyond current code when sealing the edges to prevent them from falling in a storm.

Expanding tests: 200 mph winds + storm surge

While engineers have gained knowledge through testing, the nature of storms is changing as the planet heats up.

Warmer temperatures — fueled by increased greenhouse gas emissions from human activities — allow the air to hold more moisture, and warmer oceans provide more energy to fuel hurricanes. Research shows that larger, more intense storms, heavier with water and slower moving, will pound the areas they hit with more wind, storm surge, flooding and debris.

A study estimated that if Hurricane Ike, which devastated Galveston, Texas, in 2008, were to strike in the warmer climate expected at the end of the 21st century, its winds would be 13% stronger and it would move 17% slower and would 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 (322 km/h) winds, complete with a water basin to test impact storm surges up to 20 feet (6 meters) high positive waves.

Computers can model the results, but their models have yet to be verified by physical experiments. By combining wind, storm surge, and wave action, we will be able to see the hurricane in its entirety and how all of these components interact to affect people and the built environment.

Disaster testing finds ways to make homes safer, but it’s up to homeowners to make sure they know the weaknesses in their structures. After all, for most people, their home is their most prized possession.

This article originally appeared on The Conversation. Read the original article.