X Cranes?

[afdengo]

Hello everybody,

I was looking at some videos on the construction of the Golden State Warriors' new arena in SF and I noticed that apart from a large number of tower cranes, at the phase of construction shown in the link below, there are two "x cranes". More accurately they are like large construction machines (like a bulldozer) bearing a huge steel boom that crosses another one to form a giant X. They have cables on them but I have never seen anything like that and couldn't really figure out what their function might be. Anyone know?

You can see them most clearly around the 2 min mark.

https://www.youtube.com/watch?v=3O5OKARHiZo

 

[dhengr]

Afdengo:
They are just two large mobile/crawler cranes facing each other. One with a large red main boom, facing right at 2:00 o’clock in the video, and the other with a large blue main boom, facing left at 2:00 o’clock in the video. These main booms will be near vertical when the cranes are in operation. The two cranes booms are being erected at the moment, just finished being assembled and rigged. The large white booms are long reach jibs (luffing booms or luffing jibs). At the moment, they are resting on their outer tips. During assembly both booms are laid out in line, on the ground. The two smaller white lattice structures on each crane boom, generally pointing upward, are jib struts. Their angles will be manipulated to raise the long reach jibs, to adjust its reach (working radius) and angle w.r.t. horiz. (luffing). After boom assembly and rigging, they put the outer tip of the jib on a rolling dolly and start lifting the main boom. This caused the jib outer tip to end up as you see them resting in the video. Now, they are ready to start lifting the jibs, and the main booms further, to put the cranes in operating condition.