Video: The spectacular, obligatory “Burj Khalifa now open for business” clip

Repost from yesterday’s headlines:

There are other daunting technological and practical problems with such a building. Aerospace engineers will imagine the most horrible thing that could possibly happen to a wing and then design it to withstand several times as much force. But aerospace engineers are working in an older technological tradition than designers of supertall buildings: certainly, the tapering profile of Burj Khalifa helps diminish the effect of the wind, but variables and unknown unknowns remain. We have only small knowledge of how such an extreme structure responds to wind-induced dynamic torque.

Guy’s a jackass, but it sure sounds good. Aerospace engineers probably have ten times the variables that structural engineers do–especially at supersonic speeds, where the dynamic properties of air change depending upon altitude, speed and temperature.

Structural engineers have had wind tunnels for quite a while, bub. And we design for a pretty stout factor of safety, at least in the US, and I’m sure SOM didn’t take any major liberties there.

Oh, and thanks for throwing in that phrase “dynamic torque” which you pulled deftly from your posterior. You may have been refering to torsional loading effects due to wind shedding, etc, which are dynamic, but they’re understood pretty well. And being the tallest object in the area makes the modeling simpler, if anything.

At the World Trade Center (whose rather different lightweight design might have contributed to the vastness of the calamity)

What Bullshit. If anything, the design of the towers contributed greatly to the length of time for which they stood. The average structure, including tall buildings, cannot without difficulty withstand the removal of a single column without experiencing what we call ‘progressive collapse’. But the WTC had a robust exterior system which permitted vast amounts of load redistribution, including the fact that the unbraced length of the axial elements was almost certainly increased greatly, and the damn thing was on fire to boot.

There are three seismic fault zones in the UAE area, although Dubai itself is thought to be at low risk because of its particular soil structure. Yet if I were enjoying the view from, say, the 140th floor…

Understandable but ignorant. Taller, thinner structures generally have longer periods of excitation and therefore experience less excitation from dynamic ground motion. The seismicity of a given region (soil type, depth and type of seismic event) will determine what sorts of frequency the building sees, but however counterintuitive it may be, you’re probably better off in a modern supertall building during a seismic event.

Khan’s amazing insight – he was name-checked by Obama in his Cairo University speech last year – changed both the economics and the morphology of supertall buildings. And it made Burj Khalifa possible: proportionately, Burj employs perhaps half the steel that conservatively supports the Empire State Building.

I doubt very much that the burj uses half the steel in the Empire State. It may be half the weight on a per square foot basis. But the Burj is almost certainly using steel with a yeild of 2 or 3 times that in the empire state, at least in the lower portions, and was designed using computer modeling which allows refinement not available prior to the Empire’s designers.

But it sure sounds good when he says it.

TexasDan on January 5, 2010 at 4:26 PM

TexasDan on January 6, 2010 at 11:11 AM