Florida is a great place to live, especially around January when it’s sunny and 24 degrees outside (76F) while all of your friends from back home are dealing with scraping ice off of their windshields every morning. In the late summer, though, this pleasant tropical paradise can sometimes take a turn for the worse, because Florida is one of the handful of places that frequently see some of the worst storms on the planet: hurricanes. As a Floridian myself, perhaps I can shed some light on some of the ways that the various local governments and their residents have taken to mitigate the destruction that usually accompanies these intense tropical storms when it seems that, to outsiders, it might be considered unwise to live in such a place.

The Storms

Hurricanes Matthew (2016) and Irma (2017) came very close but the centers of the storms were far enough away to limit damage in my area.

Before getting into Florida’s extremely robust building codes and unique building materials and styles, lets take a look at a hurricane itself. A hurricane is categorized on the Saffir-Simpson scale based on its maximum wind speed, which is a loose correlation to how much damage the hurricane will cause if it makes landfall. For tropical storms one can expect to lose a few palm fronds and dead branches from trees, but a category 5 storm can level entire communities.

While more intense storms can be incredibly dangerous, its important to realize that the strongest winds surround the eye at the center, and the wind speed falls off exponentially as the distance from the eye is increased. This means that a grazing blow by a hurricane will not see anywhere near the destruction that will be caused around the eye’s path. Further, the northeast corner of the eye wall tends to be the most devastating part of the storm, which is what saved Florida (and myself in particular) last year when Hurricane Matthew grazed the east coast of the state, keeping the more powerful part of the hurricane largely offshore.

Hurricane Andrew (left), a Category 5 storm which in 1992 was the costliest hurricane to make landfall until Katrina in 2005. Hurricane Floyd (right) made landfall in North Carolina as a Category 2 despite its much greater size, although at this point it was Category 4. Photo courtesy of http://geoalliance.asu.edu.

It’s also important to note that the force that the wind imparts on any object goes up with the square of the wind speed, which means that the difference between a category 1 hurricane and a category 3 hurricane can be striking, even though the wind speed only increases by 16 mph. (This is the same effect by which drag on vehicles increases exponentially with increased speed.)

Engineering Our Way Out of It

One of the more obvious solutions to living in a place like this is to simply use more robust materials when building homes and other infrastructure, and indeed that is the case for some modern homes. A common construction method, although slightly more expensive, is to build homes out of concrete block and then to fill the voids in the block with poured concrete. From there the roof can be made of concrete in some situations or can be made of heavy wood with reinforcing metal braces. Using metal as a roof surface material, rather than shingles, also helps improve the home’s tolerance to wind. Additionally, bridges, buildings, and other infrastructure are built more robustly as well to withstand the high winds of a hurricane. The skyscrapers in Miami, for example, are built to withstand wind speeds of 140 mph to 180 mph (depending on when they were built), which is certainly a higher design consideration than the skyscrapers of any other city like Phoenix or Detroit, for example.

A concrete roof is lowered onto a hurricane-resistance concrete house. Photo via B&A Architecture.

For homes that are made out of wood, however, special attention is made to how the roof is attached to the walls, and how the walls are attached to the foundation. One quirk of how high winds affect homes is that they tend to lift the roof upwards and off of the structure. To prevent this uplift, metal hurricane straps are nailed to all of the roof rafters and the roof is nailed with more hurricane straps to the wall. The wall is, in turn, bolted to the concrete foundation with special concrete anchors. These straps and anchors allow wind loads to be evenly distributed to the ground, and for the roof to resist any upward force.

Minimum wind speed (mph) design criteria for buildings and structures in Florida.

It might seem counter intuitive that the hurricane would lift the roof upwards, but as a result of the wind’s flow over a structure uplift is generated in much the same way as an airplane wing. This is why, in addition to making sure the structure itself is as sturdy as possible, the weak points of the structure must be reinforced as well. Often with hurricanes the damage isn’t so much from the wind, but from what the wind blows. And, if a 150 mph wind picks up a 2×4 or tree branch or fence post and launches it into a normal window, that opening will allow wind to enter the home and generate even more uplift to rip the roof off of the structure.

An opening of 1% of the size of the windward side of a building is enough to remove a roof. For that reason, specialized hurricane shutters are fitted to windows and doors or the windows themselves are built out of special impact-resistant glass that will shatter but remain intact, thus helping to protect the rest of the structure. Additionally, no modern building code in Florida allows for homes to have doors that open inward so that the entire jamb can take the brunt of the wind, and not just the latching mechanisms.

There is one other impact that hurricanes can have on the areas they reach, and that is torrential rain and flooding. While there’s no feasible way to build a flood-proof building, a choice of building site based on flood plain maps that the federal government maintains is often prudent. Also, living on barrier islands that are prone to storm surge is not advised either although building on stilts can help lessen the damage from a surge. On the other hand, some storms like Hurricane Harvey are so unprecedented that there is often nothing that could have been done that would have improved the situation at all.

Even with the improved building codes in Florida, no amount of concrete or hurricane straps would have prevented all of the damage that Hurricane Andrew caused, and no amount of drainage systems would have prevented all of the damage that Hurricane Harvey caused. Certainly there are risks to living in a place like Florida, but there are some pretty big rewards as well. While the winters are more tolerable than most of the rest of the United States, the surf can be pretty gnarly, and until I can afford a home in California or Hawaii this will have to do.



Source link