WOT- Cranes on tall buildings

[DaveNH]

Just returned from a job in lower Manhattan, installing
some telco equipment. Got a chance to go see where
WTC stood. I was there once, I did a job on basement floor 6.

I lack the vocabular to desribe my emotions.
Needless to say, I am saden once again.

While there I noticed that there was some contruction using huge cranes that sat on top the buildings during construction. It was an awesome site to see a couple of tons of steel being hoisted up 30, 40 floors!

A question I ask one of the locals was
"How do they get the crane down when they're finished." He lived near there and replied
"I don't know! I never though about it."

So does any one know how they really get those huge cranes down?

 

[Anonymous Poster]

There are a few buildings where the cranes have been left on top because it was more cost effective than taking them down would have been.
When the crane is removed, it's brought down in small sections using a jib boom and hoysting winch, sort of a reverse of the technology that was used building them big buildings in 1930, such as the Empire State Bldg. Until 1970, it was common for hand cranked winches to be used constructing NYC buildings. Currently, the small jib setups require 1 Ironworker to handle the cable and rotating handle, and 1 electrician to operate the electric winch. Can you say featherbedding? The best part, Ironworkers and Electricians don't have the same lunch period, so the jib only works about 6 hours a day.

 

[MDNick]

One piece at a time, and it's gonna cost a darn site more than a dime!

I always wondered how it got up there in the first place. That building getting constructed started at ground level. With a crane on it. Then it grew, but the crane goes up at the same time. And they don't have a crane to pull up the crane. Amazing.

Nick

 

[RobS]

Most tower cranes are "self climbing". They have an arrangement to raise themselves up above the tower then bring up a new tower segment with the crane and insert it in the gap. Set the crane down on the new section and repeat as many times as needed and reverse the whole process to take it down. <A target="_blank" HREF=http://www.liebherr.de/content/std_fs1.asp?sprache=us&nav_id=9&n1_id=2&n2_id=9>Liebherr</A> in Germany is one of the prominent manufacturers /w3tcompact/icons/smile.gif

 

[Anonymous Poster]

What makes you think they didn't have a second crane? The usual trick was to have at least 2 cranes, and use them to lift each other. When the building is finished, one crane is left on top, and the second is lowered to the ground in at least 3 pieces, boom, carbody, and counterweight. This was quite a common practice in the era prior to self climbers and hydraulics. Latice boom cranes that require a crew to assemble are virtually worthless today due to the labor involved in assembling the boom, until you get past 30 tons of capacity.

 

[Hoosier_Daddy]

Some use the shaft of the eventual elevator.....

 

[njrqs]

Most common here is to have the crane on the outside, so it attached every floor and then it just jacks itself back down the outside.

As said earlier, the top section of the crane has a jack unit in it, and the crane lifts a new box section up and slots in in the space made by jacking itself up.

Boy you ought to see the size of the footings used to support all that weight !!

Cheers

Sometimes it can be in the lift shaft but that gets messy as the crane has to go once the lift needs to go in.

But yes they use smaller and smaller cranes to lift them down until the smallest last crane can litterally be carried down by hand.