Up and down

"Up and down,

Up and down, 

I will lead then up and down.

I am feared in field and town.

Goblin, lead them up and down."

-- Puck, in Shakespeare's A Midsummer Night's Dream, Act III

The up and down elements of a structure are in theory vertical, but Chicago in 2021  oblique structural elements are becoming visible for everyone to see. (It seems to be happening worldwide.) Maybe oblique members have become newly available in structural analysis software. Are oblique elements a new fashion statement? Are they attempts at humanizing engineering or dehumanizing architecture? 

I don't know, but I sure see a lot of them lately.

The use of angled beams in structures has been around more than a century, but such members were always hidden. (Flying buttresses may be related to cross-bracing, and once flying buttresses were subjects of  disdain.) Cross-bracing was highly visible in San Francisco's Maritime Plaza (originally Alcoa) of 1964 and in Chicago's 875 Michigan (widely known as the Hancock Tower) of the early 1970s (both SOM). The cross-bracing serves different structural aims in these builings, and they were designed in different studios. If I recall correctly, the visible bracing in both was originally disliked and considered an engineering intrusion onto the aesthetic of the building and the city. But now the cross bracing of both those is consided a distinctive and attractive part of the skyline. 

The structural system called the diagrid seems different, and but oblique columns are more related to megacolumns because both are designed for huge lateral loads. Diagrid elements do experience lateral loads, but there the goal is stiffness thru multiple members. The oblique beams I'm looking at are connected to only a handful of other members.

One recent use of oblique structure as a design element can be seen at the building 800 Fulton (800 W Fulton Market, SOM, 2021).  The cross-bracing allows for column-free interiors. SOM used the same external cross-bracing, and for the same reasons, on a nearly simultaneously constructed building in Sydney Australia. Both that building and this one are in hip, new economy parts of town, where creativity and innovation would be valued. The building in Sydney is about twice as high, and doesn't seem to have the angled terraces of the Chicago structure. I like both.

Expressing or revealing structure is a key part of a Chicago architectural style. Here's an instance of exposed structure, on an residential tower in the Loop, at 215 W Washington (2010, SCB).

I can guess as to the structural rationale for this truss: the building's overhang required some stiffening, which was achieved through a truss. (Or perhaps it's impossible to build caissons close to the landmarked historic stucture, so that a cantilever and truss are required.) But the aesthetic choice of exposing that truss seems intentional, and it gives a fascinating contrast with the historic 1873 Washington Block, one of the first buildings constructed after the great Chicago fire: ornamented vs utilitarian; late 19th vs early 21st century; Italianate vs PoMo; old vs new. (Although the Washington Block deployed cutting edge technology for its day, it went to great lengths to conceal it.) The truss also echos the elevated train tracks, thereby linking the building to its context and also making the coarse utilitarian train part of the building's heritage. 

I found a rather subtle instance of non-verticle columns at River Point, the 52 storey building in downtown Chicago at the confluence of the north and south branches if the Chicago River. The building was designed by the New Haven CT firm Pickard Chilton. It fronts a highly visible park featuring a bright red abstract sculptue by the Spanish sculptor/architect Santiago Calatrava. Fronting the park is a large parabola of glass, which is slanted.

Behind the slanted glass are slanted columns. This photo might not convey how far these columns are from verticle, so here's a very rough estimate. (I actually did this calculation on the back of an envelope.) Interpreting the photos is difficult, but the columns appear to be about 20 ft in length and the offset--the distance between the bottom and top--is maybe 5 ft. So those columns meet the ground at roughly 75 degrees.

Perhaps one of the most visible use of oblique structual members is the new tower at 110 N Wacker Drive, also known as the Bank of America Tower. Finished in early 2021 and designed bt the firm Goettsch Partners, it features huge obliquely angled members creating a public plaza facing the Chicago River.  

This plaza allows for a view of another amazing structure, 150 N Riverside, which also created public space facing the river, and also designed by Goettsch Partners. Both buildings feature some bravado engineering: huge cross-bracing and stupifying cantievers.

It is worth remarking on these buildings, and others in the downtown Chicago area, with their strong visual identities, have emerged from a firm which traces its roots back to Mies Van der Rohe. I think these buildings are all structurally expressive and share with Mies a powerfully subtle sense of proportion; but unlike Mies' buildings, they are not minimalistically regular. 

While Goettsch has displayed oblique beams on other Chicago structures, other designers have used them.  A highly visible example is at 300 N. Michigan, which will be a 47 storey mixed use tower with a hotel, retail, residential, and offices. The building was designed by the firm bKL Architecture.The  building's branding features the truss.

Some of the oblique columns can't carry any gravity load, as can be seen from the location of the columns on the second floor.

I could point to other example of how trusses and cross bracing are now considered attractive, not to say acceptable. Trusses and cross-bracing have been part of Chicago's built environment for over a century, but putting them on display is new.

All photos bt the author.