Industrial History: Three point lift of an I-74 arch segment

(Satellite, the new bridges have yet to be captured as of Sep 2020)

I've been recording construction photos of the new I-74 bridges across the Mississippi River. Lately, I've just been saving the links because the construction has been well documented by the I-74 River Bridge Page. But a comment on the following post provided some information that makes it worth featuring with these notes.

I-74 River Bridge posted three photos with the comment: "We’re making progress on the Illinois-bound arch! Another segment has been installed this morning. At the top of these two segments are the stay cable connections."

Ben Stalvey shared

Well the MLC 650 makes this job look easy.

Mark Gallik

Excellent 3 point lift! What are the yellow parts in the load path? We commonly used chainfalls for adjustable rigging, but I'd imagine you can't buy one for that weight. Steamboat jacks?

Before discussing Mark's comment about a 3 point lift, let me note a couple of observations. First of all, with that much boom, imagine how stable the barge has to be so that the load doesn't "wobble." That would explain why the barge has four spud bars. Normally, I see only two. I wonder if those bars can partially lift the barge out of the water.

Secondly, note how small the workers are. We can see some at the bottom of the first photo on the barge and others on the work scaffold at the joint in the first and third photos.

At first I was confused about "3 point" because I saw four connections. But in this closeup of the second photo we can see that the cable from one side of the top connections goes through a pulley to the connection on the other side. That pulley turns two degrees of control into one. Specifically, that leg of the rigging controls the height, but not the rotation, of the segment. The other two legs control the rotation as well as the height. Note that two out of the three legs have a yellow thingy. As explained below, those yellow things are hydraulic rams that control the length of the leg. So I think the riggers will align the far upper corner of the segment first and then adjust the left leg to align the near upper corner and then lower the right leg to close the gap at the bottom of the segments.

Photo 2, zoomed

The new software for Facebook and Google blogging makes it a real pain in the neck (and shoulders, I spend too much time at the keyboard) for formatting comments. So I'm going to go with a screenshot.

Jordan Ent replied to Mark's comment
Enerpac Hydraulic turnbuckles. We stock them at our PA branch.
Enerpac has made these to conform to ASME standards. There are several safety features built in that will engage/lock the load if/or in the event the hydraulic system fails. Enerpac has engineered an amazing system.

I checked out the Enerpac web site. At first, I found just catalog items such as heavy lift rams...