How much wind load did the Vehicle Assembly Building withstand during Hurricane Matthew?
Let me start by stating, in no uncertain terms, that I am not a structural engineer. I am also not a genius (hush, peanut gallery). I didn’t even stay in a Holiday Inn Express last night. So, super smart brainiac-types, you can sheath your slide rules and programmable calculators — I know that I might not have this exactly right.
What I am, however, is a person who took some publicly-announced information, and plugged it into some formulas meant to determine wind loads on various structures. Yay, spreadsheets!
If you read my piece about how Kennedy Space Center (KSC) fared after being battered by Hurricane Matthew, then you’ll know that both KSC Center Director Bob Cabana and KSC Damage Assessment and Recovery Team Chief Bob Holl stated that Hurricane Matthew’s winds at ground level were 75 knots, and a blustery 118 knots above 100 feet (30.48 meters).
That comes out to 86.31 mph (138.9 km/h) and 135.8 mph (218.5 km/h) respectively. Not exactly a gentle breeze.
While much of Florida is relatively flat, with no ground near Cape Canaveral rising to, or above, the 100 foot mark mentioned by the Bobs, that doesn’t mean the fiercest winds blew by the Cape with nary a thing to push against but empty space. Not by a long shot.
A simple glance at the NASA facility is all one needs in order to notice that it has quite a few buildings rising well over that 100 foot mark, with the gargantuan Vehicle Assembly Building (VAB) reaching the lofty height of 526 feet. That’s 160 meters for you metrically-inclined people. So, quite a lot of the VAB was exposed to the strongest winds Matthew generated at KSC.
Oh, and did I mention that the VAB, though beautiful in a rockety-history-futurey sort of way, isn’t exactly svelte? Quite the opposite, in fact. The building is essentially a big box, with towering, flat sides. So, if one were going to design the least possible aerodynamic structure, the VAB is practically a textbook example.
Luckily, the building was constructed with hurricanes in mind. Because Florida.
While I was watching the press briefing about the hurricane’s impact on the center, I wanted to hear how much force was exerted on the VAB. But no one ever mentioned it…so I thought I would give it a shot.
I figured the Internet must be rife with information about how one could go about determining wind load imparted on a flat building. It is.
One of the simplest formulas is:
F = A x P x Cd
Gosh, I think I almost fell asleep writing that. I love engineering and science, but I hate the math behind it. Yes, I know, it makes no sense. Let it go.
Basically, that formula states that the force (F) is equal to the area (A) of an object multiplied by the pressure (P) of the wind, multiplied by the drag coefficient (Cd) of the object. Pretty straightforward.
I didn’t necessarily want to calculate the load on the entire structure, especially since the wind speeds decreased below 100 feet, so I decided to focus on something I knew was well-above that mark: the NASA “meatball” logo on the side of the VAB.
Now, from pictures and such, one may get the impression that the meatball isn’t terribly large. If you’re one of those people, you can disabuse yourself of that notion right now. Everything about the VAB is big, and that includes the things painted on it. Each stripe on the flag is as wide as the busses that take people on tours of the Center.
The meatball? It’s big, too, covering 12,300 square feet (nearly 1,143 square meters). That roughly the same area as five average-sized American homes, or the typical politician’s ego. So that gives us the ‘A‘ part of the equation.
Let’s skip the pressure for a moment and move to the coefficient of drag. According to the site I used for the formula: “The standard coefficient for a flat plate such as the face of a building is 2.0 for a long flat plate or 1.4 for a shorter flat plate.” I’m pretty sure the VAB qualifies as a ‘2.0’. There is no unit assigned to the drag coefficient, simply a number. So, now we have the ‘Cd‘ portion of the equation.
Two down, one to go.
Finding the pressure of the wind is slightly more complicated, but not terribly so. Since I was interested in imperial measurements, I used the following formula to find ‘P‘:
P = 0.00256 x V^2
So, that’s 0.00256 multiplied by the square of the velocity of the wind (in miles per hour). The product is the pressure of the wind measured in pounds per square foot. With the top winds measured at 135.8 mph, that means the pressure of the wind at that speed was 47.21 pounds per square foot.
Now we have all three components necessary to complete the basic calculation. Are you getting the idea that the number will be big? Because it is.
When all those are plugged into the equation, it looks like the NASA “meatball” on the side of the VAB may have been subjected to 1,161,380.72 pounds of force during the strongest sustained winds.
Let that sink in for a moment. Nearly 1.2 million pounds of force exerted on just the meatball logo. Even at minimal Category 1 wind speeds of 74 mph, that comes to almost 345,000 pounds of force on the logo. And the building was subjected to this strain for hours. Incredible.
Of course, this is a basic formula, and I’m fully aware that there are other variables that may be in play…but for this simple exercise, I think it’s pretty clear that the VAB held firm in some incredibly tough conditions.
What are your thoughts? Am I way off the mark? I’d love to hear from those better versed in structural engineering to see how close, or far, I may be to the actual number.
As always, thanks for reading.