Commercial tower. High rise building construction with a steel frame
Class 16 - Session 1 continued



I'd like to go back in time. This is the construction of the World Trade Center Tower. It was done in the early 60s. To the best of my knowledge, that was the first use of tower cranes. In this picture. It's a wonderful picture. The cranes hardly look like cranes. It's basically just a platform carrying the engine and a drum for the cable. It hardly resembles the cranes as we know them.

I'd also like to point out the boom on this crane. This is called a luffing boom. This designation of luffing boom simply means that the crane's boom can be raised and lowered and usually indicates a much higher capacity crane. You may be familiar with tower cranes, where the boom is in a fixed horizontal position, and the load is carried by a little trolley that rides back and forth on that horizontal arm. Those are much lower-capacity cranes. This is a higher-capacity crane. It was certainly the kind of crane they needed for the heavy lifts required here.

This was the first use of a climbing tower crane in the United States. What is not at all clear to me is how this actually climbs. There are none of these supports visible in the picture. The supports may occur at a somewhat lower level where they're hidden, but I'm a little suspicious of that. I'm wondering how this climbs.

This is the first time I've actually given this any thought and what jumps into my mind - and I guess if I was out there building this- I would have one crane lift up one of the adjoining cranes and raising it to the next position, and then fixing it in place. Now, I have no idea how it was done, and it may be done exactly as I have described it.

One way or another, the cranes went up with the building, and I guess the assumption was they jack themselves up the way modern cranes do. That may or may not be correct. Whether or not they had long hydraulic cylinders in those days that could actually lift the crane by one story at a time or more, I really don't know. I'm somehow questioning that. And just judging from the appearance here, it looks like they are not visible and some other method was used.