re-post with update: old (other) Chicago skyscraper of the week–Santa Fe elevator

31 December 2022 Update: The State of Illinois has sold the 23-acre site on which the Santa Fe silos (now known as the Damen silos) stand to the owners of MAT Asphalt, a company with a checkered history of influence and community relations in Chicago. MAT’s owner has indicated they intend to demolish the silos and redevelop the site sometime next year.

Some loyal readers will know that, alongside my research on commercial high-rise construction, I’ve very happily gone down a rabbit hole the last few years chasing the history of the city’s grain elevators–Chicago’s “other” skyscrapers. That’s a comparison that was made by many at the time–Inland Architect said in 1896 that “the first sky-scraper was a grain elevator,” and when the Montauk was built in 1882, at 130 feet it was shorter than seven of the grain elevators that lined the River at the time.

That history is, I hope, going to be the subject of a published paper sometime next year–the city’s elevators were instrumental in its role as a financial center, and even though there are only a handful of structures left–and none from before 1900–their influence can be seen in Buckingham Fountain, IIT, Wacker Drive, and the U.S. Supreme Court…it’s a doozy of a story.

But they also impacted building as a whole, pioneering technologies that were adapted by commercial skyscraper architects once they’d proven themselves. Mechanical transport, temperature monitoring, and pile foundations all saw proving grounds in grain elevators, sometimes decades before their application in buildings for people.

One of the most influential pieces of technology transfer came from Chicago engineer John S. Metcalf, who constructed one of the first concrete grain silos in Indianapolis, and who was commissioned by the Santa Fe Railroad in 1906 to build silos and an elevator for their freight yard at Damen Ave. and the Chicago River. Like most elevators, this one was designed to buffer the flow of grain from points west, arriving by rail, by providing storage and a docking facility for lake barges that could carry the grain to points east. Its location, two miles upstream from downtown, speaks to the congestion that was plaguing the River by this point, but it also illustrates the position of Chicago as place of exchange and transfer–the Santa Fe was one of over 100 elevators built before the Depression that allowed the city to absorb the influx of corn, wheat, and other grains from the midwest and Plains states.

Metcalf’s innovation was to apply a new material–reinforced concrete–to the problem of grain storage. Concrete was fireproof, a big improvement over the timber elevators that had been constructed throughout the 19th century, but one that required skilled carpentry to build the cylindrical formwork needed to build silos that could, by incorporating hoops of reinforcing steel, resist the fluid pressure of a hundred or so feet worth of vertically piled grain. In 1904 and 1905, Metcalf patented a system of moving formwork that used donut-shaped forms, about four feet tall, to pour one day’s worth of concrete at a time. The next morning, after a pour had cured to a working strength, laborers would crank the forms up another four feet, using steel rods embedded in the concrete as rails to support the forms and their attendant scaffolding platforms, and to assure that they rose truly vertically. Scientific American referred to Metcalf’s innovation as ‘quite as simple as it is ingenious,’ as it reduced costs for concrete construction below those for steel.

Metcalf built thirty-five silos out of concrete for Santa Fe in 1906, paired with a head house constructed of timber that housed the elevating machinery and the ‘marine legs’ that could take grain up, or discharge it, into waiting barges. In 1932, the wooden head house burned, but the concrete bins were unharmed by the fire and the railroad commissioned Metcalf to rebuild the head house in concrete. Both of these structures–the original 1906 bins and the rebuilt 1932 head house–are extant but in ruins, abandoned by the railroad in the 1970s and taken over since by the State of Illinois. Given the importance of slip-form construction to concrete high rises, Metcalf deserves more credit than he’s ever had as the inventor of this system. He also, along with engineer Jason MacDonald, also of Chicago, deserves recognition for building an astonishing number of slip-formed concrete elevators throughout the United States and Canada, and for revolutionizing the type; after Santa Fe, all grain elevator construction in Chicago, and most of it throughout the midwest, switched from timber to concrete.

The Santa Fe is one of just four pre-WWI elevators left standing in Chicago–in addition there are two along the Calumet River and one (threatened) in the West Loop. Metcalf’s pioneering bins are the most visible of these, though, as they can be seen from the Stevenson Expressway and the Orange Line CTA. They deserve some sort of landmark designation as one of the last links to the most important trade in the city, and for their own quiet beauty–the end elevation of the 1906 bins is, frankly, something a lot of architects would be happy with today.

CHSA 2023 at UIUC–call for papers

Happy to report that the Construction History Society of America will a) hold its next meeting from 22-24 June, 2023, and that b) the University of Illinois at Urbana-Champaign will host it.

This is a happy change in schedule–since 2006 we’ve held biennial meetings based on what had been a relatively relaxed flow of new research and papers. Over time this proved to be a bit awkward whenever the triennial International Congress synced up with us. Since the next ICCH is going to be in 2024 (in Zurich, more info here), and since the American field has grown quickly, the CHSA Management Committee has decided to hold annual meetings in subsequent years, filling in the gaps between the every-three-year International gatherings.

Marci Uihlein and I will co-chair next Spring’s meeting on the (beautiful) campus of the University of Illinois at Urbana-Champaign. We have a website that includes the just-released call for papers, also included below. More to come on keynotes, tours, and social events, but for the moment mark your calendars and please share this CFP widely. Our meeting this past summer at Kennesaw State in Georgia was a demonstration of how far the field has come in the Society’s brief existence and we’re looking forward to even broader participation from preservationists, historians, architects, engineers, and general enthusiasts…


Construction History Society of America announces CALL FOR ABSTRACTS for the 2023 Biennial Meeting on Construction History

Held at the Illinois School of Architecture, at the University of Illinois at Urbana-Champaign

June 22-24, 2023

We invite researchers and practitioners from all aspects of the history of construction to submit paper abstracts on subjects for the 2023 Meeting on Construction History, to be held in Urbana-Champaign, Illinois. The meeting will be hosted by the Construction History Society of America and the Illinois School of Architecture at the University of Illinois at Urbana-Champaign and follows successful meetings of the CHSA held in Marrietta, GA (2022), Seattle, WA (10th Anniversary Members’ Meeting 2017), Austin, TX (2016), Minneapolis MN (2014), Cambridge MA (2012), Philadelphia PA (2010), and Atlanta GA (2008).


Abstracts will be compiled in a hard-copy catalogue to be distributed at the meeting.  Presenters will be asked to give their talks within 20-minute time slots.  A curated Proceedings, including completed papers of 4000-6000 words, will be assembled and edited by the Scientific Committee following the conference.

Additionally, CHSA encourages authors to also submit full papers to Construction History according to their publication schedules. The submission of an abstract for the CHSA Meeting does not exempt papers from the Journal’s review process


  • authors’ names and institutional affiliations
  • an abstract of 300 words.
  • key words (selected, if possible, from the list of topics and subjects),
  •   a one-page curriculum vitae indicating contact information, status, laboratory affiliation if relevant, and publications or other relevant work for each author.
  • All presentations must be in English.
  • 4-5 learning objectives, for use in AIA CES documentation.


• Construction and engineering in Chicago and other regional cities

• Rural and agricultural construction, particularly in the Midwest

• The role of education in the building professions, especially in the region

• History and construction of specific projects

• History of the building trades or specific builders

• Organization of construction work

• Wages and the economics of construction

• The development of building codes and regulations

• Trade unions and guilds

• Military or Army Corps of Engineers

• Structural analysis and the development of structural forms

• Development of construction tools, cranes, scaffolding, etc.

• Building techniques in response to their environments

• Building materials, their history, production and use

• History of services (heating, lighting etc.) in buildings

• The changing role of the professions in construction

• Building archaeology

• Computer simulation, experimentation and reconstruction

• Use of construction history for dating of historic fabric

• Recording, preservation and conservation

• Construction in architectural writing

• The role of construction history in education

• The bibliography of construction history

• The theory and practice of construction history


Dec. 15, 2022                                                Abstract Deadline

TBD.                                                          Online Registration Open

Mid-Feb., 2023                                             Author Notification

April 15, 2023                                                Author Registration Deadline

June 22-24, 2023                                           Conference

google to SOIC–this is…good?

The saga of Helmut Jahn’s State of Illinois Center/Thompson Center seems to be coming to a happy end for preservationists and Loop advocates with the news that Google will buy, renovate, and occupy the building (headline writers can’t resist adding “after long search…”)

Google’s move reverses a worrying trend of disinvestment as commercial tenants have been leaving the Loop in droves as remote work has encouraged alternative locations and office arrangements. Anchoring the center of the city with a few thousand employees is a good thing for transit, for retail and dining establishments, and for the city in general.

From a preservation point of view, it remains to be seen whether Google lives up to the not-totally-fulfilled promises of the 1986 building. Always a public favorite, access to its glass atrium and rotunda (stunning but environmentally dubious) is in question, as are its iconic Miami-Beach-on-Clark-Street curtain walls and postmodern? deconstructivist? follies that worked better as axonometric drawings than public sculpture. Jahn’s original curtain wall design was supposed to combine structural glazing with insulated glass, but this proved beyond the capabilities of manufacturers and installers in the 1980s. With Google’s deep pockets maybe this gets revived, though the basic physics of its southwest southeast-facing, 14-story glass atrium can’t help but present environmental challenges. (Thanks for the correction, Kevin G.–your proofreading merit badge is on its way…)

Less heralded but equally good news, IMHO, is the announcement that the State will decamp from the Thompson Center to the “old” Harris Bank/BMO tower a few blocks south. Designed by SOM and built in the early 1970s, it’s a vastly underappreciated example of the firm’s most rigorous work, with a finely tailored stainless steel curtain wall and central core elevators that are effectively suspended above the ground floor lobby and accessed by escalator, leaving the space wide open. It’s a subtle building, and hemmed in enough by its neighbors on La Salle Street that it’s hard to notice, but worth a look–especially as it presents a neat contrast with the first Harris tower, also by SOM, on the eastern end of the block. That was designed by Walter Netsch, a rare skyscraper by him, and the contrast between the gothic-like tracery of Netsch’s tower and the robust, if latent, classicism of the later one, by Bruce Graham, is pretty clear.

State of Illinois had a complex history. It emerged as the last, long-delayed element of Mayor Daley’s plan to keep Federal, City, and State offices downtown and as the sole piece of the ill-fated North Loop revitalization plan championed by Arthur Rubloff. If that had gone through, much of the area east and north of SOIC (including, unbelievably, Rapp & Rapp’s iconic Chicago Theater) would have been razed, replaced with megablocks and skywalks that, in hindsight, would have been disastrous. Jahn and then-governor James Thompson both saw the utility in producing a striking, press-release-worthy building, but making the complex geometry and giant atrium work proved difficult. The project suffered cost overruns, declining support in the local press, and serious thermal and water infiltration problems. Budget cuts eliminated new furniture and even doors on private offices–one wag at the Tribune noted that, finally, the State was living up to its promise of “open government.” But the atrium and basement food court (a new innovation in 1986) were immediately popular with workers and the public–the building regularly was cited as both the “most hated” and “most loved” building in the city.

If Google keeps some public access, if it leverages its ownership into much-needed improvements to the CTA station attached to the Center, and if it invests in restoring or replacing the building’s cladding, this will prove to be a good thing. I’ve written critically about the efforts to landmark and salvage the Thompson Center before–I think the costs and consumption needed to keep energy-hogging buildings alive and running has to be taken into account when we have these conversations–but if Google is picking up the bill and if it’s willing to keep the best aspects of the building while fixing the most difficult this could be a win…

st. john’s

It’s been a great irony that, with all the traveling to see Nervi buildings I had not–yet–been to the one closest to my home base. St. John’s University in Collegeville, MN hired Marcel Breuer to masterplan their campus in 1953 and the central church, with its iconic bell tower, was the centerpiece of Breuer’s extensive work on the campus. Its design and construction paralleled that of the UNESCO conference hall, which Breuer designed with Nervi and Bernard Zehrfuss from 1955-58. (The best design history of the structure is Victoria Young’s Saint John’s Abbey Church: Marcel Breuer and the Creation of a Modern Sacred Space (U of Minnesota Press, 2014).

The two projects have immediate similarities–but also key differences that are interesting as insights into two very distinct but related careers. UNESCO has always seemed important to me as a moment where two really thoughtful approaches–Breuer the International Style modernist and Nervi the process- and pattern-oriented structural engineer–merged for a very brief moment and profoundly influenced one another. Breuer emerged from the projects as a confirmed brutalist, interested in the expressive power of exposed concrete and robustly displayed structure, while Nervi’s work expanded into more sculptural (if far more restrained) territory.

UNESCO on the left, St. John’s on the right. Both house a large assembly space under a folded concrete plate roof–the corrugations give thin concrete planes the depth necessary to act as beams, and you can see that both structures rely on deep, stiff connections between vertical and horizontal members to become portal frames. Breuer clearly appreciated the architectural impact of the folded plates–their deep recesses create a strong pattern of light and dark that gives both spaces rhythm and scale. Crucially, though, the folds run the long direction of the UNESCO space while they run the short direction of St. John’s–perpendicular to the liturgical axis:

The effect is recognizably gothic–the structure emphasizes the march down the aisle to the altar, which is notably open and pushed forward into the congregation as an early experiment in what would become standard design in post-Vatican II churches. So far, so good. Nervi thought that gothic churches represented a high point in structural and architectural integration, and would have been entirely on board with Breuer’s sensibilities here.

How those corrugations landed, though, was a matter of contention. Breuer wanted the heavy roof to sit above strips of windows that would illuminate the sanctuary from ground level–making the concrete appear to float. Again, not unlike gothic structure, but look at where the folded plate/portal frames land. Their loads are collected by a deep concrete girder that carries them over apertures to the bearing piers. That’s a bit of structural gymnastics of the sort that Nervi criticized heavily. A good gothic builder (or, for that matter, Roman or Greek) would have “put solid above solid,” both a recipe for structural efficiency and for visual satiety. Syncopating the structural rhythm of the plates and windows does make for a striking visual–but for Nervi this was a distraction from the otherwise holistic conception of the structure and space. While he wrote–extensively–about UNESCO, Nervi rarely mentioned St. John’s, and from correspondence it’s clear that he considered this a less successful manifestation of the folded plate idea than the conference center in Paris.

Nervi was farther from Collegeville than Paris, of course, and that shows (perhaps) in the quality of concrete. As a contractor, Nervi’s knowledge of formwork and mixes was extraordinary and the craft that went into the surfaces of his poured-in-place work is rarely given the credit it deserves. UNESCO’s concrete shows the level of fine detail that would have come from having that knowledge going into design, specs, and site supervision. St. John’s concrete is far rougher, and Breuer was happy to have the random color differences and rough surfaces that would come to typify brutalism on display. Both approaches work, and Breuer’s late career would take this acceptance of concrete ‘as-stripped’ much farther.

So, a far less “pure” Nervi work and one that relied more on his calculation than design instinct. That doesn’t take away from the sheer architectural power of the Abbey, though–Breuer on a good day could produce genuinely awe-inspiring spaces with the best of them, and you can see him starting to stretch his sculptural and spatial instincts as well, beyond the relatively straightforward efforts in his houses to that point. In particular, the balcony, set up on cantilevered piers and grazing but not touching the back wall of the sanctuary, is a tour de force, or, really, a tour de forces, that is almost Wrightian in the way it compresses and explodes as you move under it:

The bell tower–easily the best-known piece of the composition–contains something of a tribute to Breuer’s collaboration with Nervi. Its base is recognizably splayed, reflecting the shape of the Eiffel Tower, which sits at the opposite end of the Champ de Mars from the UNESCO building.

Collegeville is about a 70-minute drive northwest on I-94 from Minneapolis and well worth the trip, especially if your traveling companion knows to recommend the bear claws at Nelson Brothers Bakery in Clearwater. If you can throw in a Twins or St. Paul Saints game or two, so much the better.

quarry stones, milestones

Architecturefarm has been offline while we relocate our main offices to our new ‘east coast’ location (in the words of an Iowa neighbor, to whom Illinois might as well have been Massachusetts when we moved in). Still, lots to report and ponder about the last semester, which was sort of bookended by two righteous quarry visits.

Our hotel studio this year was based in Rome, amongst the Nervi Olympic projects–full details to come, but the highlight was a field trip that we felt needed to make up for our students’ two years of being stuck at home. In addition to Rome, we took them to Florence and (split-squad) to Venice, Bologna, and Mantua, exactly the sort of whirlwind tour that I’ve usually tried to avoid. In this case, though, we agreed with the studenti that an antipasti tour that whetted their appetites for more, future travel was only too appropriate.

My teaching partner, Lee Cagley, offered Carrara as a day trip. This has always been a bucket list stop for me–picturing Michelangelo stomping around picking the perfect piece of marble is irresistible (even if apocryphal), but Lee’s background in high end hospitality design came with connections that made a day there even more extraordinary, with a Land Rover tour throughout the mountains, lunch in the foothills, and a back of house visit to a shop that let us see the marble get gradually refined from massive blocks into architectural and sculptural pieces.

My seminar class on building history puts stone construction near the very start of the syllabus, comparing it with timber in the way that materials not only have to be fabricated and assembled but also harvested. Timber is relatively easy, but stone obviously requires another orbit of technology–cutting, shaping, transporting, etc. Seeing the scale of the operation and how challenging it is even with giant machinery puts a lot in context and makes it clear that proximity and the existence of good paths or roads to get the stuff off the mountain and into the shops were determinant factors in stone architecture. (Watching giant trucks hauling multi-ton blocks down cliffside gravel roads from the back of a Land Rover drives this home rather well…)

Base camp included an open-air museum of quarrying techniques, replacing those giant tractors with…wedges and water, an ancient technique still used into the early 20th century that relied on the expansion of wetted wood to crack large pieces into more manageable sizes:

A slightly different vibe this past month at the 2022 Biennial Meeting of the Construction History Society of America at Kennesaw State in Georgia, where tour day involved descending into the pit of an aggregate quarry. At Carrara, aggregate is what happens when they hit a bad vein or a stone breaks poorly–a way to salvage what they can out of what would otherwise be an expensive bit of rock. Marietta is all gravel, all the time–one of hundreds of local quarries that provide the raw material for roads and highways instead of finish stone for buildings. And while the scenery wasn’t quite coastal Italy, the scale was still impressive.

Both places naturally spur questions about extractive industries and renewability–seeing the amount of earth carved away and scaling it to a century in Marietta’s case or a couple of millennia at Carrara makes it clear both how abundant the raw stuff of building is in the earth and the expenditure of raw power it takes to remove it. Students on the tour in Italy asked a lot of hard questions about the impact on the local environment, and that pipe in the middle ground of the Georgia quarry is there to pump a pretty toxic brew of ground water out of the pit and into a treatment facility. The scale of the equipment also makes it clear why building and buildings account for 50% of our energy consumption:

Any chance to get students, in particular, to see the roots of their choices is an important part of understanding the larger contexts of what we as architects do, so Carrara was a great moment. It was also part of a milestone semester, in that it was the last time Lee and I will teach our integrated hotel studio together; he’s off to enjoy a well-earned retirement. He and I have enjoyed five years of coaching teams of interior designers, architects, and landscape architects into working together, finding overlapping interests, subtly clashing value systems, and the frustrations and rewards that come with trying to meld all of those into coherent pieces of design. Have we swept a few Hospitality Design student competitions along the way? Made wrong turns and ended up on the wrong continent? Hiked bands of students up a volcano or along the shoulder of an Italian autostrada? We have. I’ll miss watching Lee at work, as he’s been a truly brilliant studio instructor, someone who has taught me as much as he has our students.

some personal news

Very happy to report that I’ve accepted an invitation to join the University of Illinois’ School of Architecture as a Visiting Professor for the 2022-2023 academic year. Champaign-Urbana will be a great base camp as Chicago Skyscrapers, 1934-1986 finishes up–the School is just a few blocks from its publisher, the University of Illinois Press. Once the book is out in the world I’m hoping for many opportunities to talk about it in and around Chicago, which will be a short train ride away.

A short ride and a familiar one. Illinois is my alma mater and Champaign-Urbana is where I grew up. That train ride was a key element in early, formative trips to Chicago, and it’s been an enjoyable reprise to take it down to campus for studio reviews over the last few months. Those reviews have featured great work and Temple Hoyne Buell Hall has been full of impressive energy each time. I’m looking forward to being a part of that, teaching alongside some good friends and at least one of my undergrad professors, as well as completing the new book in particularly appropriate surroundings.

Thanks to all who have made this happen…

structures zoo–desktop tensegrity

Our rough schedule for the Structures Zoo course is to go from heavy to lightweight, introducing students to more and more exotic structural types as we go (sort of like going from the goats in the petting zoo up through the penguins, orangutans, and eventually the lions…) We’re closing in on the end of the semester, and the last lab or two should be doozies, but the more recent one definitely turned a corner as we went from membrane structures to what I think of as networked structures.

The paradigm for these is the geodesic dome, invented by (or, really, rediscovered, packaged, and marketed by) Bucky Fuller. The evolution of the dome through his initial attempts at Black Mountain College (and, I think, at Chicago’s Institute of Design, but that’s another post), shows a gradual refinement from structures based on flat members arranged in “great circles” that failed, to geometric patterns that arranged nodes around a spherical surface, connected by multiple linear elements. The result was a structure with vast redundancy–like a monolithic concrete structure, a true geodesic presents a nearly incalculable number of potential paths for gravity and lateral forces to take. As a result, it functions very much like a shell structure, but with nearly all of the weight removed.

Exotic enough, but all of those elements are sized to take either tension or compression. A particular variant of the geodesic experiments, (pictured at the top) involved figuring out how to organize the linear elements so that compression and tension could be isolated–in other words, placing the heavier, compressive elements only where they were needed and rendering the rest of the dome in thinner, lighter, tensile elements–cables.

The instigator of this idea was Kenneth Snelson, who went on to a career as a sculptor and consultant for all sorts of projects employing this principle. But Fuller also co-opted it, calling it “tensegrity” and (depending on who you believe) claiming it as his own. While geodesics were a bigger business success, tensegrity ranks higher on the exotic structures spectrum because of the uncanny openness the principle creates:

Super weird-looking, right? But also completely stable. If you start at the base, you can see that the structure is based entirely on triangulation–think of it as a three-dimensional truss. Each compression element has its ends stabilized by three cables, fixing those two points in space. As long as you can trace those cables through other, similarly fixed points back to the foundation (the nice, boring equilateral triangle at the bottom), the whole thing is stable–at least mathematically.

First steps–none of the spaning elements are stable in the (roughly) left-right plane yet, but this group is figuring out that those sticks need to be fixed top and bottom…

So, on the desktop, using wood stirrer sticks for compression elements, regular string for tension, and duct tape to make joints, you can very quickly and simply build a network of triangulated members, finding stability where you can and fixing points by watching where the structure is floppy or where it feels fixed. Student teams started with sterilite boxes, and quickly realized that the secret to building these is that you have to go down to go up–that some tension elements want to pick up gravity loads by reaching down (thus ensuring that they’ll always be in tension), while you can use the compression elements to gain height–with impressive results. A second ‘family’ of cables stabilizes the compression elements’ upper ends, fixing points of triangles to give the whole structure geometric stability.

One team went with a precedent study, building an analogue version of the structure that held up the (now-demolished) Georgia Dome. You can see the “go down to go up” principle at work here as the structure “climbs” a series of (red) compression elements to gain height. Again, there’s some missing rigidity in the short axis, but they’ll get there.

These get impressive pretty fast–here’s Rob admiring that first team’s finished product, a cathedral-like tower of sticks that seems to float almost by magic, even if you know the trick (also, in the background, ace knitterbot sculpture by ace ISU digital fabrication team, for inspiration).

The Georgia Dome is still among the best examples of the principle at work in practice, and its limitations are apparent when you start poking at these models–even with all of the triangulation you’re dealing with inherently flexible structures, and once you realize that you have to design for wind-related lateral forces and uplift in addition to gravity the deflection issues get more difficult. But the results are, to say the least, visually compelling, and tensegrity’s material efficiency is remarkable.

So, what’s lighter than light? That’s this week’s lab…

tabletop nervi

Salone “B,” Torino Esposizione

In post-Nervi lecture Q&As, this question almost always comes up: what made his work so architecturally distinctive? My answer is that Nervi not only designed the structure of his buildings, he also designed the process (thus the subtitle of the book). In particular, since he was the contractor for most of his early work, he sought ways to reduce his costs by breaking down the large spans he built into smaller elements that could be fabricated by relatively unskilled crews, usually in parallel with excavation and foundation work. Distilling structural form into pieces that could be made and, more to the point, placed by small crews kept his equipment overhead low and it allowed him to telescope construction schedules. But it also imprinted his buildings with a definite grain; if all of his pieces were made at a human scale, their agglomeration into a long span would, inevitably, also express that human scale.

In short, I like to say, Nervi’s structures may have been large, but they were productively simple; in fact, if you had enough space and enough time, you could build the Turin Salone B (above) in your backyard–the basic units were made using the simple process of ferrocemento, or light cement troweled onto cages of steel mesh, and they were designed to be light enough that they could be hoisted into place by three or four laborers and a winch.

That combination of process and product has served me well as a great teaching example and, teaching a structures elective with Rob Whitehead this semester, we had the chance to put it into actual practice. Instead of building a full scale version in the parking lot (someday…) we decided to have two teams see if they could replicate the process at two smaller scales; one team fabricated 1/8 scale ferrocement elements with materials from the local hardware store, while the other used 3D printing to produce smaller scale elements, which they assembled during class in a piece of performance art/architectural gymnastics.

Ferrocement proves to be a lot like a loaf of bread: remarkably easy to make a good one, really hard t make a great one. This group got a lot right, making a mold out of foamcore and bending mesh over it–a pretty precise analog to the actual fabrication process that Nervi’s crews used. Quikcrete proved to be tough to work with, though, as it cured too quickly to get good finished edges or to get a full piece made monolithically in one attempt. But the process was fast, and as you can see from the structural test, they were both light enough to assemble by hand and robust enough to at least handle their self weight and resulting thrusts (assuming proper buttressing–Tara is doing a good job there…) Their appearance bothered some of the team, but the actual Nervi units were surprisingly crude, not all that dissimilar from the finish (or lack thereof) here–but they cleaned up well with a coat or two of plaster and paint on their undersides.

The modeling team had the advantage of farming out their fabrication to the school’s 3d printers, but they ran into similar fabrication issues that were analogous to real on-site problems. It took a few tries to get the orientation right (note the incomplete ones in the back), and to get them produced in a reasonable amount of time–the first efforts took something like eight hours to fully print. Getting the time-per-piece down was key to getting them all ready for class, in the same way that simplifying the algorithm in the job site yard was vital to getting hundreds of ferrocemento elements produced just in time to start hoisting them into place.

Our plan had been to have one team assemble a wooden centering that would replicate the traveling scaffold that Nervi used to hoist and place the units, but Nervi didn’t have to deal with errors in scaling in Rhinoceros, so while there’s a beautiful piece of centering in the pic above, it ended up being purely ornamental. We did have a team pour the buttresses while the 3d printing was going on–telescoping the assembly time–and at this point sort of considered delaying the assembly until we could get the scaffolding done to the right scale. Fortunately, the printing team had come up with a snap-tite connection detail in the units that allowed them to assemble multiple elements “off-site,” giving them just enough structural integrity that they could snap larger pieces onto the buttresses–no centering needed (or, really, human centering applied). It took a couple of tries, but once the pieces were all in place the resulting arch was just monolithic enough that it stood on its own, and even survived some tentative testing.

We’ll call it a modest success–certainly an accurate analog to one slice of the Turin hall, and (we think) a valuable lesson in how process–fabrication and assembly–influence and sometimes determine structural form, alongside actual statics. Lots that we would/will change for the next iteration–better cement, more attention to getting the centering right, and maybe jumping scale. Still, certainly proof of concept in that this structure–seventy plus years old at this point–has much to teach.

The best part? I’d given the class a line about making an “IKEA drawing,” or an instruction sheet, for how the process would work–based on the illustrations done by a then-grad student for the book. And did they take the opportunity and run with it? They did.

Graphic: Tristian Thao

structures zoo–jello column

After ten years, things have cycled around to give my colleague Rob Whitehead and me half-course elective slots at the same time, so we’ve pooled our resources and put together what we’ve always talked about as our ideal structures class–one long session every Friday morning dedicated to hands-on structures labs. These have always been our favorite parts of teaching structures and, we think, the most effective since they get concepts off of the whiteboards and out of the textbooks and put them into the real world. Breaking stuff and getting students to talk about how and why failures happen is inherently messy and something of a tightrope act, but that mimics the real world, where nothing is ever quite as pure as the formulas make it seem.

Structures Zoo has been colossal fun to scope out and start to put together. We had our first class yesterday, which was basically our thesis statement–that structural knowledge and awareness comes from our interaction with the actual world, and that we make the most progress (as a species and/or as students of the discipline) when we take a rigorous approach to assessing what works and how. We set the first class up as a structured set of four labs, each tied into the history of the deflection formula. Starting with Archtyras and Archimedes, there’s a very neat history-of-science approach to how we understand the deformation of a beam under load–I’ve written before about using this as a way of showing that structures has always been a scientific enterprise, subject to revision and addition as new technology (including Arabic numerals, algebra, calculus, etc.) has come on-line.

The final lab of the day tried to drive home how efficient the scientific method can be, and how quickly it can produce actionable and testable knowledge. The “E” in the formula above is Modulus of Elasticity or a numerical measure of stiffness (also called Young’s Modulus). That’s an intimidating name, but it’s really just a simple ratio of stress to strain–in other words, how much a material deforms under a given load.

In column theory this is most useful in helping to understand how a “long” column will buckle–you want a stiff material that will resist the tendency to get out of the way of a load and start a death spiral of deflection, increased bending forces, further deflection because of those forces, and failure. But in “short” columns–those not vulnerable to buckling because of their stout, hockey-puck-like proportions–“E” is really simple to measure if you have an accurate enough rig.

Or a squishy enough material. If you’re trying to do deflection calculations on steel, you’re dealing with a Young’s Modulus of something like 29,000,000psi. Here at Big State U., we do not have testing rigs in the Architecture department that can impart millions of pounds of pressure, so we have to scale things down. As it happens, there’s a very convenient kitchen staple that can put us in the desktop range of deflections and loads quite easily:

Jello’s natural squishiness (or, in technical terms, very low Modulus of Elasticity) means that it deflects enough to assess with a tape measure and some light weights. We fabricated columns with various concentrations of gelatin (Disclaimer: actual Jell-O is engineered for a much softer mouthfeel, making for an unworkable column, so we switched it up and went with Knox unflavored gelatin instead), all using high-tech formwork (yogurt tubs with the surfaces oiled for easy removal) that produced nice round columns of equal diameter:

To test them, we simply placed one-pound (ish) cans on a bearing plate that let us measure the height of the columns before and after loading. Adding weights one at a time let us plot a rudimentary stress/strain curve. In an ideal world, the slope of that curve is equal to the Modulus of Elasticity, and a simple calculation lets us put a number to that figure.

And, of course, we loaded them to failure, giving us a yield stress that marks the top of the curve:

Stress on the Y-axis, strain on the X-axis

Depending on the quantity of gelatin in the column, we got Modulus of Elasticity figures ranging from .8 psito 5.4 psi*, but the shape of the curve was interesting–those figures were the average of a slope that changes from a shallow slope to a steeper one. What that means is that the columns deformed more under the initial load, and underwent some kind of “strain-hardening” as loads increased–they got stiffer under higher loads. We hypothesized that this was due to the colloid nature of the gelatin, since the initial loading pressed excess water out of the material. As that water was pressed out, the material consolidated a bit and got tougher to compress. Further research may be necessary.

Doubling the quantity of gelatin made for a pretty stiff column (relatively speaking), but also a strong one–in addition to deflecting the least, it held the final test weight of 15 pounds without failing. Generic blueberry “gelatin dessert” didn’t do much as an additive, as you can see on the right.

All good fun, but with a point. The math behind our most common structural situations can get pretty simple, and the same forces that govern our largest structures can be observed and played around with at any scale. Similarly, we’re able to change any number of variables when we’re building–shape, scale, and material–but we only know how those changes impact what we’re trying to do by testing them out. And, finally, we’re firm believers that while knowledge can come out of textbooks and formulae, wisdom only comes out of taking those ideas into the real world and seeing where they work and what their limitations are. Hoping to take those principles into our weekly Friday sessions each week this semester…

*When we first thought of jell-o columns we were convinced it was an original idea, but a quick online literature search turns up numerous other efforts at determining the material properties of gelatinous desserts. We’re pleased to report that our measurements support conclusions reached by other squishy-column researchers…we stand on the shoulders of giants, etc., etc.