Starting from a distance, an up and down burst out like a torrent of heavy rain. But on the ground, its behavior can be more destructive.

When the blasting wind hits the ground, they shoot horizontally in all directions, sometimes breaking windows and reversing with enough force.

As our latest research shows, these winds behave in complex ways, especially in cities. An explosion up and down can deflect tall buildings, thereby increasing pressure on windows and walls of nearby buildings. The result may blow out the glass and shatter from the facade. Even buildings designed to survive hurricanes can suffer major damage in the up and down eruptions.

As engineers, we looked at the goal of designing buildings, components such as solar panels and windows, and infrastructure such as power lines that can withstand this powerful force. To do this, through field measurements, we created our own powerful descending explosion using the hurricane walls of Florida International University.

What is decline?

Explosions may be as destructive as tornados, but their wind development develops in very different ways.

When the thunderstorm cools down and heavier air drops from high places in the atmosphere, an up and down burst occurs. As the rain-cooled air poured downwards, it increased its speed. Once it slams into the ground, it has nowhere to go, but goes outward and emits strong winds in all horizontal directions.

The wind speed of the descent explosion can reach more than 150 miles per hour. This is the advantage of a Category 4 hurricane, powerful enough to knock down trees and wires, damage buildings and flip vehicles.

These winds also rotate, but not like tornadoes. Storms are often considered straight winds, but when the winds bend on the ground, they rotate about the horizontal axis. Instead, the tornado rotates around the vertical axis.

A powerful storm system called DERECHOS is usually composed of multiple explosion clusters, each containing many smaller downward explosions, sometimes called microexplosions.

Recreate Houston's up and down outbreak in warehouse

On May 16, 2024, a Derecho attacked Houston, and it exploded so strongly that it blew up and down the windows of several high-rise buildings that were designed to survive in a category 4 hurricane. The wind also took off most of the exterior walls of the buildings.

Two months later, Hurricane Berill hit Houston with similar wind speeds, but caused great damage to downtown buildings.

To understand how such a downward explosion could be more destructive – and what cities and architectural designers can do – we simulated the downwind eruption in Houston and the winds of Hurricane Berill on the wind wall.

The test facility is equipped with twelve jet fans, each of which is as tall as the workers who run them and powerful enough to simulate a Category 5 hurricane. Our team uses these fans to recreate powerful downward tides, with these bursts of winds hitting horizontally with maximum wind speeds approaching the ground. We then placed several building models in tests to see how the structure of the roof, windows, facades and power cords reacted under that force.

[embed]https://www.youtube.com/watch?v=Z_W-4S34IAE[/embed]

During Houston Detro event, the descent explosion exploded 100 mph winds. It cracked some lower windows, possibly blowing fragments, but also caused general accidental damage midway through some buildings.

The Chevron Building Auditorium actually suffered the biggest loss, and this was not directly on the storm line, but facing another tall building. That left some interesting questions. It shows that the way the building may have caused a strong suction force, causing the tower to blow out the windows midway. Another burning question is whether the design code is outdated when building design codes in terms of how their cladding is versus the extent of these local wind energy.

Using the wind wall, we were able to test these pressures on models of Houston buildings and see how the winds erupting up and down increase the pressure on tall building models with too much force approaching the ground.

The ability to simulate these winds is important to improve engineers’ understanding of the differences in how explosions and other wind events exert forces on buildings. The results ultimately provide information for building standards to help create more resilient and more protective communities.

Build a better power cord

Large storms (such as downward tides) can also remove power lines.

Power lines extend hundreds of miles between cities and states, making them more vulnerable to locally severe storms, such as outbreaks. If one of the towers falls, it can cause a chain reaction, such as domino falls one after another. This can eliminate abilities for a large number of people.

Together with colleagues, we have been testing transmission towers and multi-power line systems under outbreaks and hurricanes to understand the responses of these structures with the aim of developing better building technologies. This work helps update the U.S. manual to design power cords, which engineers use to design safer, richer gearbox towers.

What's next

Low-rise and medium-rise buildings are also susceptible to up and down outbreaks, but the impact is not well understood. Explosive winds are strongest between 10 and 300 feet on the ground, meaning that some lower levels of roofs and walls may be hit by strong horizontal winds.

Recent building regulations provide design guidelines to help ensure that these buildings can withstand tornadoes. However, in a short time in a building or building community, the way the drop erupts exerts pressure on the walls and roofs in different ways. Similar to straight winds, we expect high suction on the roof. Due to short duration, changing wind direction and strong wind speed, downward bursts can also lead to excessive vibration and changing pressure distribution of roof components.

[embed]https://www.youtube.com/watch?v=u5povpflgg8[/embed]

Now, we are testing down explosion damage to low and mid-rise buildings to better understand the risks and help highlight changes that can make the building more resilient.

As the population grows, cities are adding more buildings. At the same time, powerful storms become more frequent and more intense. Understanding the impact of different types of storms will help engineers build high-rise, low-rise and wires that can better withstand extreme weather.