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Empire State Building - Wind deflection.

Empire State Building - Wind deflection.

Empire State Building - Wind deflection.

Today I was asked by my daughter - how far does the ESB sway due to wind ?.  (One of her neighbours had suggested three metres !!).  

Tall buildings are not in my area of expertise, so I visited the ESB official web site, and found this:

"The Empire State Building does not sway...it gives.

With a wind of 110 miles per hour, the Building gives 1.48 inches.

Movement off centre is never greater than one quarter inch, thus measurable movement is only one half inch, one quarter inch on each side".

On the face of it, there seems to be an inconsistency here (unless this is a pure PR statement, in which I ought not to expect fact or logic?).

I can live with the semantic refusal to call deflection under wind a "sway", (presumably the PR team at work?).  However, I would welcome any explanation how the maximum deflection can be quoted as 1.48" in one sentence, and 0.25" in the next.

Wouldn't even 1.48" be remarkably low for a 1250 foot high building?

RE: Empire State Building - Wind deflection.

AUSTIM, even more remarkable is that in the late 40s or early 50s the ESB was hit by a war plane and even more incredible the damage was very local.

If you're an "experienced" engineer like me you might just remember that bit o' trivia!!

RE: Empire State Building - Wind deflection.

It's not obvious that there is an inconsistency.  It may very well be that the building "gives", e.g., deforms under wind load, so that the windward wall moves 1.48 in, but the CG only sways 0.25 in.

RE: Empire State Building - Wind deflection.

A deflection index of H/500 is considered pretty good based on additional stiffening being provided from interior partitions and masonry cladding, which the original ESB had in spades. I suspect the 0.50 inch value is the interstory deflection.

A total sway of 2.5 - 3.0 feet would not be extraordinary, and may in fact be a lower bound value.

RE: Empire State Building - Wind deflection.

More speculation...the ESB has a very heavy stone facade, which would tend to decrease its response to vortex shedding and other oscillating wind effects.

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