21 Boston – 03 – Tower Crane

A new piece of sculpture has showed up in the neighborhood – a tower crane ! There have been lots of them downtown; and now upper Queen Anne has one of its own.

It’s quite visible from a number of vantage points, and striking up close,

and as it fits into the retail core along Queen Anne Avenue.

This Tower Crane will make it possible for the 21 Boston – Safeway Grocery Store / Housing project to take big strides. The crane seemed to arrive suddenly; but it’s actually been a deliberate, well-planned process. The Compass Construction Company helped make it understandable with some graphics, snacks, team members to answer questions, and hard hats for the kids.

One of the most dramatic features of the crane is the length of the jib arm – a 267 foot radius. That means that it can swing over nearly all of the large site as well as over 3 of the 4 adjacent streets, though the loads that it carries will be over the site and the assigned street level truck delivery areas.

The initial steps taken for the crane installation had occurred earlier. An impressively massive and deep concrete foundation was poured; and the first piece of the tower fastened in place.

This piece of the work is critical because the moving balance-beam nature of the crane requires an absolutely solid and stable base. Other work, like the installation of the waterproofing for the walls proceeded for a while, giving the concrete base time to sufficiently ‘cure’ before taking the weight of the crane.

Then things really got rolling. Compass brought in two mobile cranes, one medium size to help unload crane components as they arrived by truck, and one large size to lift the various parts of the tower crane in place. Here a lower piece of the tower is headed for installation.

As each segment of the tower was lifted into place, workers hand-guided their extensions into the matching openings in the segment below. Double bolts on each leg were power-wrenched in place. The grey safety work-baskets are placed there for the workers and then are moved up to the next connection as needed.

Finally, the turntable caps off the top of the tower. It contains a giant gear into which the crane motor gears will bit and be used to turn the jib.

Finally (for this day) the vertical part of the tower crane is capped off with the Operator’s Cab and the Tower Peak.

The remainder of the job would be done the following day. Friday provided a beautiful day for completing the Tower Crane assembly, sunny, blue skies, no wind. With the vertical elements already in place, the first horizontal piece to go up was the Counter Jib, the “back” arm of the crane that balances the loads carried by the jib. In the picture below you can also see the jib sections laid out in the staging area, waiting their turn.

With the counter jib in place and braced by the diagonal rear pendants, the first jib section is lifted towards the operator’s cab. You’ll notice that this piece of the jib also has a peak (on the left) – not always the case. This tower crane needs to reach out over a full block site from one side and requires a longer jib to do so; and that extension needs its own peak and pendant extension.

Here you can see the core of the operation, with the pendants on the left yet to be diagonally fastened in place.

Next comes the jib extension itself, a big lift for the mobile crane, not so much for the weight as for the balancing and turning required to get it lined up with the rest of the crane.

And here’s the whole tower crane, with smaller elements like the counter-balance weights being added at the end.

It will be in action over the site for the next couple of years.