It is time to stop quivering in our boots in pointless fear of the future and just roll up our sleeves and build it.
- Ray Pierrehumbert

Saturday, August 27, 2011

A concern

Quoth NOAA:
MORE SO THAN WITH MOST STORMS...THE WINDS WITH IRENE INCREASE

SHARPLY WITH HEIGHT ABOVE THE SURFACE. AS IRENE MOVES THROUGH
AREAS WITH HIGH-RISE STRUCTURES...THESE BUILDINGS COULD EXPERIENCE
WINDS SIGNIFICANTLY STRONGER THAN THE SURFACE WINDS. WINDS AT THE
30-STORY LEVEL WILL LIKELY BE 20 PERCENT HIGHER THAN AT THE SURFACE
...AND WINDS 80-100 STORIES UP COULD BE ABOUT 30 PERCENT HIGHER
THAN AT THE SURFACE.
OK, that's bad enough because power goes as the square of velocity (and damage as the cube, or something like that).

But as I ponder it this seems even scarier than that. If the storm is still symmetrical when it hits Manhattan, I could imagine that there could be enough tall structures to set up turbulence that could mix momentum back downward. Is this crazy? Suppose a sustained 60 mph wind over Manhattan heading north to south. It hits midtown hurricane force winds at 30 stories start mixing up with all the artificial canyons and crevasses and mix down?

What are the maximum sustained winds independent of altitude? How high up are they?

Will the streets of Manhattan be covered in glass tomorrow? Are highrise buildings unsafe under these conditions?

I hope not. I love New York. But I'm not sure this situation has any precedent.

12 comments:

Oale said...

The safest places should be the innards of a sturdy lowriser building 3rd floor upwards for the storm surge, if one cannot/wants not to leave the threathened area, I suspect

Nick Barnes said...

On the 22nd floor of an apartment building in Hell's Kitchen, overlooking the Lincoln Tunnel entrance, I'm pleased to report that it's been really boring so far. Quite rainy, and they closed the tunnel for a while, but other than that nothing to report. Even the trees I can see are not much affected so far. Touch wood.

Oale said...

http://g.co/maps/7waa

Robert Grumbine said...

For precedent, or at least as close to one as you get, look for "Long Island Express". iirc it was 1934, but don't trust that day beyond +- 50 years.

muoncounter said...

You don't have to look far for a precedent for this type of damage: Houston, Hurricane Ike. Vortices and downward flow were indeed a factor.

During Alicia, downtown Houston sustained major glass damage, largely due to loose gravel on flat roofed buildings in and around downtown. Here's another good summary.

Call it the 'urban glass island effect.'

Aaron said...

We can build to withstand any storm, but it is expensive. Here in California, I had to fight with my roofer to have him work to Dade County, Fl. building codes. It added 3% to the total cost. He did not think that I should waste my money.

The problem is that we can not look to past weather as a basis for engineering design. Today we need to engineer for weather events that 30 years ago were considered impossible.

David B. Benson said...

Structural engineers are aware of the urban canyon effect and attempt to account for it in proper design. The major issue is structural integrity; can't have tall buildings falling down.

Window breakage is another matter. To be brief, the main reason is flying sand or larger projectiles (roof gravel, whatever) in hurricane force winds. The hard material fractures the glass which then shatters. If no projectiles, modern windows will withstand the simple air pressure as was demonstrated by houses directly subjected to the full force of Hurricane Katrina.

Steve Bloom said...

Austin plugged with a 44 in keeping with the old Western tradition and you don't even mention it? :)

Michael Tobis said...

Nicely put. Hottest damn day of my life. 44 C or 110 F.

Hottest August day ever in Austin, but tied for second place on the annual scale.

Not fun.

Steve Bloom said...

Hmm, Steve Scolnik says tied, but for the all-time daily record.

Jeff said...

FYI, Force is squared, power is cubed, damage is ?? x ?? + ?? in the range of velocities expected from a hurricane.

muoncounter said...

Old hurricane-patch wisdom: "Hide from wind, run from water." Wind speed damage estimates only tell a part of the story, as we've seen with Ike's surge and now Irene's flooding.