Balance ball in a skyscraper

[Steven]

I have just come across something very interesting that helps to protect buildings in case of an earthquake. The taipei 101 for instance contains a 724 ton balance ball that is moved to counteract the buildings movement due to wind speed and earth shakes.

http://deputy-dog.com/2008/06/22/in-act ... sing-ball/

[Saribro]

The Burj Al Arab also has tuned mass dampers in it's columns to dampen vibrations caused by vortex shedding from certain directional winds.
With the ever increasing height of buildings, and their slender construction caused by architectural demands, other methods of retaining stability in vibration need to be implemented.

[Ciro Pabón]

Thanks, Tomba, nice link. There are other means: J-dampers, gyroscopic dampers, liquid slosh dampers.

Nowadays most tall buildings use one, not only for earthquakes but for the wind, as Saribro explains. You HAVE to use them: buildings up to 40 stories can rely only on shear wall and steelbraced core systems, which are very effective in resisting the forces and deformations due to shear racking. However, the resistance of these systems to the overturning component of drift decreases approximately with the cube of height. Unless you want to spend a fortune in bracing, you have to use dampers, not only in buildings but also in bridges.

I swear you can see the bathroom water at CN tower and Empire State to slosh around the basin on a windy day. At the Jhon Hancock building they were installed after people got sick. http://en.wikipedia.org/wiki/John_Hanco ... ating_sway

[majicmeow]

I can attest to the CN towers movement in high wind.
Depending on where you are standing inside the building, and what point of reference you choose, you can actually see the building move.
I did not check the water in the washrooms, but I'm sure it was moving pretty good!

I did place my iPhone on the floor of the building and watched the accelerometer data as the building moved. I'm not sure exactly how the iPhones accelerometer is calibrated or what the values work out to be, but they were moving in sync with the building.

[nae]

even in a small tower block in which i stayed
if , on a windy day, you placed both feet on the ground and
both hands on the walls you could feel the building sway

fortunately the FIA don't govern building standards thus
allowing tuned mass dampers to be used, at least in this
case its clearly is an aero device

[Steven]

Fortunately the FIA don't govern building standards thus allowing tuned mass dampers to be used, at least in this case its clearly is an aero device

hehe

Anyway, such devices were unknown to me before I discovered that page.

I am aware however of Japanese buildings being constructed on top of a special suspension system in order to whitstand earthquakes, but I guess that won't be able to counteract winds.

[rjsa]

I first learned about these in a Discovery documentary about the Citicorp Building. The story is interesting, it could collapse on 45 deg winds as was built and was secretly refurbished.


Here the 1995 New Yorker article:
http://www.duke.edu/~hpgavin/ce131/citicorp1.htm

[vyselegend]

What I found very impressive also is that they can add a further 724 tons near the top of a skyscrapper without compromising it's structural integrity or overloading the base. Of course 724 tons means nothing to the global weight supported by the foundations, but wow, we're dealing with amazing numbers here!

[checkered]

As far as I can

understand, it's an exciting time in tuning high-rise buildings for different structural loads. Not entirely surprising, then, that developments in design tools yield solutions that seem familiar accross different engineering disciplines - everyone functions within the possibilities of physics after all. TMDs are "second generation" solutions, but direct applications are gaining ground. Here, fluid viscous dampers are coming onto their own on a scale that from an automotive perspective is fairly staggering.


Torre Mayor, linked from http://www.construction.com


Torre Mayor damper, linked from http://www.scotforge.com

Torre Mayor (2003) in México City recently stood out as an example of such design. Its interlocking diamond pattern truss damper system was envisioned by WSP Cantor Seinuk. Standing at 225m, the 57 storey office tower sports 98 dampers in a "Damped Link" arrangement. Torre Mayor has already withstood earthquakes and is said to be among the safest skyscrapers ever built - I saw a documentary where some of the workers noted that a fairly major event didn't even register with them, they were only being informed about it via friends or news. Arup seems to have developed their own "Damped Outrigger" concept, which is already being put to use. I'm sure there are other more or less interestingly comparable systems also. Some links:

Torre Mayor
WSP feature on Torre Mayor
Damped Link Element in Coupled Truss or Wall System, by Ahmad Rahimian (WSP) in STRUCTURE Magazine, Nov. 2007, PDF
Viscous Dampers Come of Age, by Wilford, Smith, Scott, Jackson (Arup) in STRUCTURE magazine, Jun. 2008, PDF