K-10000 tower crane
F.A.Q.

#01


QUESTION

ANSWER
At what wind speed will tower cranes of the hammerhead type topple over, assuming a 100% proper installation.  Having a large wind area at the top of a tall skinny tower, tower cranes  just do not look very stable.  

 

 

1.  TOWER CRANES IN GENERAL

Tower cranes are less prone to blowing over than what one could think by looking at them.

It is important to note that at wind speeds above 40 - 50 MPH, depending on the make and model, all hammerhead tower cranes must cease operation and allowed to weathervane, i.e. left free to swing with the wind.  Because the front jib is much longer than the cw jib, the jib will follow the wind direction, and the cw jib will point against the wind, so the actual wind area is a lot smaller than the broadside surface.  The wind sees the jibs from the end, not the side.

Furthermore, tower cranes are substantially counter weighted.  A typical tower crane will with zero hook load have a reverse moment which is equal to the forward moment when the crane has its full design load at max radius.  As a consequence the tower will be in balance, i.e. there is zero moment, when the crane has half its full design hook load at max radius.

The substantial reverse moment when out of operation comes into helping the tower crane in high winds.  It takes some wind to overcome the reverse moment, it takes more wind to equal full load moment, and it takes yet more wind to overcome the strength of the tower.

Tower cranes in the sizes used for building construction are by European Codes required to withstand a wind speed of 100 MPH.  When such cranes are at their maximum allowed free-standing height, they are unlikely to withstand winds much above 100 MPH.  Winds above 100 MPH are, however, extremely rare.  We are aware of only one tower crane which went down solely because of high winds.

2.  K-10000

The K-10000 tower crane is most unlikely to be toppled by high winds, because of its very large reverse moment and its enormous tower strength.

It takes a wind speed of 115 MPH to cancel out the reverse moment, i.e. in a wind speed of 115 MPH there is zero moment at the tower base.  Purely as a mental exercise, solely to illustrate the point, one could unscrew the nuts of all the anchor bolts securing the crane to the footing.  They are not needed in a 115 MPH wind; but they are needed as soon as the wind subsides, so don't try it.

It takes a wind speed of 175 MPH to cause a moment at the base which is equivalent to the moment in operation with max. design hook load at max radius.

Consequently it will take a wind speed greater than 175 MPH to topple the K-10000.

Much of this numerical data can be visited from the DETAIL page by selecting CONCRETE FOOTING and go to the bottom of the page, then click on:
TOWER CRANE BASE REACTIONS - U.S. UNITS

  

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Copyrightę 1999 Tower Cranes of America, Inc.
Page Last Updated On 09/14/1999