chicago spire back on track?


Courtesy Chicago Architecture Foundation

There’s a buzz this weekend around the news that Shelbourne North Water Street LP has found a backer to help it out of bankruptcy, possibly paving the way for work on the dormant Chicago Spire to start up again.  I’ll confess that the mechanics and legalities of the finances are well beyond me, but the support of Atlas Apartment Holdings LLC out of Northbrook is nearly the first positive news the project has had since work stopped in 2010.

As Lynn Becker points out, Atlas isn’t exactly a household name, and Shelbourne left plenty of burned bridges as the project folded in the wake of the 2008 housing crisis.  Chicago’s market has recovered, but most of the investment right now is in rental apartments, not in condominiums, which make up all of the Spire’s proposed program.  The proposed influx of investment would only get previous debts paid off, leaving the question of financing the project’s re-commissioning and construction open.

There’s been plenty of speculation that getting the Spire re-started, built, and sold could in fact be possible in today’s market–after all, if there was ever a project geared toward the very healthy 1%, this is it.  Lots of comment pages have pointed out, though, that even in a hot market the relatively small apartments (on average) seem out of step with the cost of going so tall, and with financing based on a luxury model.  And with Calatrava’s press recently, some of the shine he brought to the project may have, um, dimmed a bit.

But to my mind there are even basic logistical problems with the design that still raise some concerns.  One of the few published floor plans shows a total of eleven passenger elevators to serve 1200 luxury condominiums.  That’s a ratio of over 100:1, where we usually think of 60:1 or 70:1 for high-end developments (even lower end apartments are often around 90:1).  Coupled with the fact that neighbors have pointed out that dead-end North Water Street isn’t really built for another 1500 cars, there are still some figures here that seem based in the weird optimism of the pre-2008 crash.

Granted, I’m not a huge Calatrava fan.  While he’s alluded to Chicago’s skyscraper tradition before, this one seems more in the Masonic Temple vein than anything else.  There’s a part of me that would like to see this, if for no other reason than to settle the “nation’s tallest” debate for a little while (remember, Chicago already has the country’s tallest building, because the top of that thing in New York is, um, just a spire).  It would be a long, long haul from this first step to get work started on the ‘bathtub’ again, but stranger things have happened.

This week’s news has at least been enough for the Chicago Architecture Foundation to put the Spire back into its city model (see above, and thanks for the pic!), so at least there’s some construction work going on…

Bill Baker lecture at NU–some Burj facts

Bill Baker, structural engineer extraordinaire at SOM, gave a great lecture at Northwestern earlier this week about Burj Khalifa.  Given that the crowd was mostly engineers, he was able to ramp it up a bit and give a few technical details that I hadn’t heard before.

The most interesting point he raised was that of all the differences between the Burj and supertall skyscrapers of even a few years ago (concrete instead of steel, e.g.) the most important one was that the program for the Burj–mostly residential, with some boutique office spaces at the top for fly-in meetings–allowed much smaller floorplates than, say, Taipei 101.  Apartments don’t need acres of contiguous, flexible space, they need as much access to daylight and views as the economics of the tower can stand.  As a result, even though the Burj is nearly twice the height of Sears (828 meters), it only has about 2/3 the floor space (3m sq. ft. as opposed to 4.4m.)  Particularly near the top, the building is basically a concrete mast with a narrow ring of rentable space around it.  This allowed SOM to design the core as a fairly simple beam against wind resistance, since the structure is almost all shear walls and therefore can’t rack like a frame.  So the numbers are big, but they’re not complicated–Baker said that you could do the basic wind calcs for the structure by hand.

OK, the cool stuff?  Concrete that was super fluid enough that the “slump test” was more of a “puddle test.”  The well-described vortex shedding shape that prevents harmonic resonance by ‘designing the wind’ (Baker said this was like a kid on a swing trying to kick 24 times a cycle instead of one, which is a great description that I’m going to steal).  Concern that entrained water in the 3.7m thick concrete mat would actually boil because of the endothermic reaction in curing concrete.  And–this was the biggest surprise for me–the tower is so tall that it benefits from adiabatic cooling.  Because the air pressure at the top is noticeably lower than that at the base, the air temperature is dramatically cooler.  So the air handlers always take their air from the top of a tower zone and feed down.  At this height they can also harvest water from onshore breezes, picking up something like 14 olympic sized swimming pools a year.  No one would call the tower ecologically optimal, but this strategy makes a good point about microclimates and building height.