August 31, 2018 § Leave a comment
(UPDATE: Sept. 6, see below)
The collapse, two weeks ago, of a span of the Polcevera Creek Viaduct in Genoa is a particularly sobering structural failure. Authorities put the death toll at 43, and beyond this is the fact that the bridge was literally a textbook example–one of the truly great pieces of structural expressionism that was, for more than fifty years, hailed as a work of structural art. Its designer, the Roman engineer Riccardo Morandi (1902-1989), was a near-contemporary of Nervi. His path took him to bridge design after a similar early career in cinema and theatre roofs. Morandi’s practice represents a shift in Italian engineering from the lingering economic and cultural influences of autarchy, which emphasized concrete as a locally-produced material, to steel, which had been unavailable in Italy during the fascist era, but which proved itself economical during the post-“Italian Miracle” era of rising inflation and thus the need for more rapid construction.
The Polcevera viaduct, completed in 1966, was his masterpiece–a muscular but finely proportioned march of concrete towers across an urban valley that provided a crucial autostrada link between Genoa and the resort town of Savona to the north. Morandi’s solution to the difficulty of the 1200-meter span was two-fold: a viaduct on the northern half of the valley supported by vee-shaped compression towers, and three cable-stayed, cantilevered spans supported by taller towers on the southern half. These spans used what would become Morandi’s signature technique, combining steel and concrete into massive pre-stressed tendons. While ordinary cable-stayed spans rely on multiple, individual strands of steel cable, Morandi’s solution gathered hundreds of these strands into single elements. Other engineers critiqued this idea, noting that since cable-stayed bridges rely on a deck that can absorb huge compressive forces, this necessitated a stiffer than normal roadway and thus a tremendous amount of extra dead weight. But Morandi argued for the technique for its elimination of costly cable maintenance. Wrapped in concrete, the steel strands would not require the near constant painting involved with the traditional fan-shaped solutions, and the resulting visual effect was particularly striking; the simplicity of the structural diagram made the bridge’s structural performance evident even to laypersons.
Construction photos reveal a great deal about the behavior of the bridge. In the above image, you can see that the decks were actually self-supporting under their own loads. They are actually supported by diagonal members that frame into the towers’ bases, and were formed by traveling formwork that balanced around each tower. This shot shows each of the three towers at successive stages–the one in the center shows just how far the decks could cantilever under their own weight, making the tendons themselves responsible primarily for carrying the bridge’s live loads.
Here, too, you can see the cables being draped from the tower on the left–not yet carrying any load. Once these were tightened, encased in concrete, and assisted by further post-tensioned cables in their concrete jacket, the short span between the two cable-supported decks could be placed. This sequence was much like that of the Firth of Forth Bridge, where the steel cantilever towers were gradually extended, and then the span between them filled with a short, beam-like infill.
This shows the steel tendons being wrapped with their concrete jackets after they’ve been tensioned–the deck is actually warping upwards, a deformation that would be corrected once the load of the spanning element was added to it.
The result was a particularly elegant bit of structural sculpture, but one that did have problems. In the 1990s, concerns about deterioration of the concrete led to a full survey of the structure, which found that the internal strands in the southernmost tendons had been corroded by water infiltration due to flaws in construction that left permeable voids in the concrete jackets. In 1996 these tendons were supplemented by steel cables grafted onto the outside of the structure:
In this diagram, by Profs. Gentile and Martinez Y Cabrera of the Politecnico di Milano, you can see both the new ‘jacket’ of reinforcing steel and a new steel ‘saddle’ at the top of the tower. Recent Google Earth imagery shows the condition of this repair recently:
The tower that collapsed was the one farthest north, where the span switched from the cable-stayed elements to the pure viaduct. In the one video of the collapse (available elsewhere), the first few seconds appear to show the tower itself collapsing, and while it’s difficult to see through the driving rain, it appears that the deck has already collapsed. If that was the sequence, it would make sense that the (now gravely unbalanced) tower would become unstable, too. Coupled with the 1996 repair of the south tower, this suggests an obvious possibility: on a busy afternoon, with a full live load, cables that had been slowly and invisibly corroding finally failed in tension, leading to the collapse of the end of the deck and then the unbalanced tower.
If, in fact, that is what investigators determine, it raises a much larger set of questions, many of which are already being shouted loudly. The bridge’s condition had, in fact, been the subject of much concern among the pubic and the engineering community–University of Genoa engineering professor Antonio Brencich went on record in 2016 as saying that the bridge was conceptually “bankrupt” and “a disaster waiting to happen,” a seemingly prescient claim that, notably, didn’t suggest what exactly would cause the failure. Calls for replacement, however, led to political headwinds; the right-wing Five Star party, now in power, has blamed budget limitations imposed by the EU, but in 2014 the party campaigned against replacing the bridge, on the grounds that such a large construction project would only encourage corruption, calling concerns about its collapse a “fairy tale.”
To complicate the politics of the collapse further, the motorway was privatized in the early 2000s, and the concessionaire, Autostrade, has mishandled the aftermath of the collapse horribly, with embarrassing claims that the collapse was simply a natural disaster (there were initial claims that the bridge had been struck by lightning just before the collapse–but this wouldn’t, on its own, have had any effect at all on the structure). The company had, in fact, been doing foundation repairs on the span on the day of the collapse, part of an unending series of patches. (Excavations during a torrential rain might suggest that the foundations were undermined, but the apparent sequence from the video and the initial survival of the tower argue against this as a cause).
In all of this, Morandi’s design has largely escaped blame, though it’s worth noting in hindsight that his revolutionary approach to stayed structures may have contributed to the disaster in at least two ways. First, collecting all of the cable support into monolithic tendons left the structure with no redundancy; if a cable on a typical, fan-shaped stayed bridge deteriorates, there are dozens of others that can carry its load, at least under emergency conditions until it can be replaced. That wasn’t the case at Polcevera, obviously. The loss of one tendon necessarily meant the loss of the span. Second, the concrete cover meant that there was no way to visually assess the state of the steel itself. Corroded or compromised steel cables can be easily spotted and accessed in traditional cable bridges. But here, it took a full survey in 1996 to determine that there was even the possibility of corrosion.
Still, Morandi was designing in an era where the expectation was that such a bridge would be fully staffed, and its maintenance fully funded over its lifetime. Deferred maintenance has become the norm in Italy and throughout the developed world, as governments and voters forget that the cost of large infrastructure is just the down payment on life cycle costs that are necessary to maintain structures’ health and integrity. Houses need new roofs every twenty years. Bridges need regular monitoring and, often, invasive, surgical repair of corroded or deteriorated pieces. The running joke in American politics this year has been “Infrastructure Week,” which keeps getting announced and then trampled by more sensational news. Meanwhile, the American Society of Civil Engineers reported recently that 9% of bridges in the United States–more than 56,000–are known to be “structurally deficient,” most of them due to lack of maintenance. 40% of American bridges are older, in fact, than the Polcevera Viaduct, meaning that whatever the proximate cause of the next large collapse here, no one should be able to get away with saying it was “unexpected and unforeseen,” the terms used, unconvincingly, by Stefano Marigliani, head of Autostrade’s Genoa bureau, to describe the Genoa collapse.
UPDATE (Sept. 6, 2018): A good overview on the New York Times website today confirms that the collapse began in the southern pair of cable stays and cites the lack of redundancy as a contributing factor…
Gentile And F. Martinez Y Cabrera (Department Of Structural Engineering, Politecnico Di Milano), “Dynamic Investigation Of A Repaired Cable-Stayed Bridge.” Earthquake Engineering And Structural Dynamics,Vol. 26, (1997). 41-59.
Prof. Ing. Riccardo Morandi, “Viaducto Sobre el Polcevera, en Génova-Italia.” Informes de la Construcción,vol. 1, no. 200. 57-99. May, 1968. Available online at: http://informesdelaconstruccion.revistas.csic.es
August 14, 2018 § Leave a comment
Watching this with horrified interest. Riccardo Morandi’s iconic A10 viaduct in Genoa suffered a major collapse earlier today during a torrential storm. The one video posted by La Repubblica shows what looks like the already damaged western tower collapsing. There are reports that traffic was heavy, it being the holiday season, and that there was maintenance being done on the bridge deck. Some reports say the tower was struck by lightning before the collapse, though it’s hard to imagine how this would be the cause. Video of the rescue efforts show windy conditions, which seems more likely a contributing factor.
The viaduct employed Morandi’s classic hybrid style–each tower was a simple A-frame with tension arms that held the ends of a compression deck. Between these were shorter spans of simple beams. Their diagrammatic simplicity was matched by (relatively) easy construction, which meant that the system was economical for his much larger project over Lake Maracaibo in Venezuela, and for the short leap that the A91 highway from Fiumicino Airport into Rome takes alongside the Tiber. Will be looking for further news and/or ideas about just what happened. La Repubblica’s twitter feed has been a reliable source this morning.
August 8, 2018 § 2 Comments
I could sit and talk about Chicago’s skyscrapers with Jen Masengarb all day–and last month I had the chance to do that (or for at least an afternoon). Jen is now with the Dansk Arkitektur Center in Copenhagen, but she was previously the director of education for the Chicago Architecture Foundation, and in that role she very generously invited me out each year to talk to the CAF docents about my skyscraper work.
She’s sorely missed in Chicago, where she’s also been a regular guest on WBEZ’s Curious City. This week they’re broadcasting highlights of a chat she and I had with Jesse Dukes, answering a listener’s question about the density of the Loop–why are the city’s skyscrapers clustered in such a compact area?
The result was, as you can imagine, a free-wheeling discussion, and the edited version is a nice, concise set of thoughts on economics, politics, urban branding, and infrastructure. WBEZ’s producers made us sound pretty efficient, and they certainly got the best out of what was a really enjoyable afternoon…
July 27, 2018 § Leave a comment
In about 2003 I was in the midst of a book project on Louis Kahn, saving up research dollars and bingeing on week-long trips to the Archives in Philadelphia when I could. After a couple of these trips, Bill Whitaker, archivist extraordinaire and friend to anyone studying Kahn, told me “I think you need to talk to Nic and Tom.”
Nic Gianopulos and Tom Leideigh were engineers at Philadelphia firm Keast and Hood. Kahn worked with both of them early in his career, and he trusted them implicitly; they had formal roles on the Yale Art Gallery and the Parliament Building at Dacca, but Kahn sought their advice on projects he did with August Komendant, too. The early stages of the Kimbell Art Museum occurred during one of many periods during which Kahn and Komendant weren’t speaking; Gianopulos describes seeing what Kahn wanted to do with the roof vaults and telling him, essentially, that he needed more firepower than Keast and Hood could provide. He’d have to go “talk to Gus.” Kahn took that advice, too.
I did get to spend an afternoon with Gianopulos and Leideigh at Keast and Hood’s offices–they were well into their positions as partners emeriti, but still kept a presence there and had several rolls of drawings to talk through with me. As with most Kahn interviews, the afternoon went back and forth between hardcore details, philosophy, and the fondest possible memories, which was evidence that Kahn’s practice was profoundly human, gloriously flawed, and yet capable of producing work that its protagonists still found breathtaking and moving forty or fifty years later. After the book came out I did a lecture and signing at Penn. In the midst of the social hour afterward I felt a firm hand on my shoulder. I turned around to find Nic, who shook my hand and said, with a smile, “you got it right.” No review has ever meant more to me.
Keast and Hood announced earlier this week that Nic Gianopulos died on July 21, at age 93. After his time with Kahn he specialized in historic preservation, and he taught at Penn for over 25 years. Would that all of us can look back on such a long, productive career, and share what we learned with such joy. Very grateful to have run across him, and to have had that brief but inspiring conversation.
July 23, 2018 § Leave a comment
A full week of engineering and design in Cambridge, MA, where the annual meeting of the International Association of Shell and Spatial Structures gave a pretty solid overview of the current state-of-the-art in advanced structural engineering. I was there to give papers as part of their Working Group 17, which documents and studies historic shell structures, but sat in on plenty of interesting sessions about what’s going on today.
There was a definite flavor to the week that a lot of the past decade’s wilder speculations have been tamed by practice–foggy-eyed papers on the possibilities of genetic algorithms and full-scale 3D printing that characterized this conference a couple of years ago have given way to papers on low-carbon processes, timber structures, and labor-saving fabrication that focuses more on making processes simpler than on manhandling complexity. For me, the signal presentation was on self-forming timber shells that relied on two-dimensional laser cutting of thin wooden sheets in patterns designed to take advantage of the material’s own tendency to shrink during curing, creating natural curvature that otherwise would have required a great deal of mechanical force to achieve.
Indeed, timber is the sexy material of the future these days, whether it’s in skyscrapers or in shells. Its relative availability, ease of handling, and (of course) renewability make it a far more carbon-efficient material than concrete or steel, while it’s light weight and ductility allow for a range of low-fi fabrication methods that are themselves relatively low-energy. Throw in that it’s a natural material with a range of textures and colors that seem friendly and you have a pretty convincing argument, one that’s being pursued by a huge number of research groups right now.
Historic shells, by contrast, seem a little ponderous these days, but there were good sessions on the field’s past, including a fair amount of dissection of Saarinen’s Kresge Auditorium, where the conference was held. It’s spherical roof, along with Utzon’s graceful but almost impossible shells for the Sydney Opera House, was one of the most important controversies in the 1950s. Nervi, among others, railed against the false simplicity of the form, and its static deficiencies are apparent if you know what to look for (hint: some of the ‘mullions’ in that elegant curtain wall are actually holding up the mid-spans of the shell’s edge beams). And in a climate of rampant optimization, it formed a pretty good foil for many of the structurally efficient shapes that appeared on projection screens during the week. (Hard to imagine, isn’t it, that a superstar architect could get away with facile form-making in an era where we have such convincing tools…)
The week’s highlight, though, was a day trip to Hanover and a group visit to Nervi’s twin sports arenas at Dartmouth. Momo Sun, a recent MIT graduate, has done ace research on the history of the two buildings, and we were lucky to get all-areas access to both buildings. They’re a study in variations on a theme–both are extruded, shallow parabolic shells formed with ferrocemento pans that add stiffening ribs to thin concrete roofs. Their respective buttressing, though, shows Nervi’s growing confidence in American concrete.
Leverone Field House, built between 1961 and 1964, uses simple in situ props with broad horizontal beams that absorb the thrusts of the roof while providing shelter for ancillary spaces to either side of the main shell. Thompson Arena, the hockey rink across the street, uses Nervi’s trademark system of twisted wood formwork to achieve dramatic, ruled-surface piers that reflect the structure’s need for ductility under thermal loading. (New vocabulary–today this gets termed ‘compliance,’ which seems much more evocative).
As interesting are the varied approaches to enclosing the open ends of each shell. Thompson’s end elevations are pretty simple precast concrete with some bracing mullions that run the full height, but Leverone’s are glass curtain walls that are steadied against wind forces with gently shaped truss members–and particularly expressive details at their tops that allows the shell to ‘ride’ vertically as it expands and contracts without bearing on the curtain wall. If you look closely, you can see that the top fixture is actually a strut with two pins–one at the connection to the roof, the other at the connection to the wind truss. It’s a similar detail, as fellow Nervi scholar Tomaso Trombetti pointed out to me, to race car suspensions that have a similar need for robust resistance on one direction and complete flexibility in the other. (Trombetti mentioned Ferrari suspensions in particular, but this isn’t just an Italian detail…). We debated for a while whether these steel trusses were actually Nervi’s designs, or whether they were imported to the project by local engineers–I’m out on a limb as saying that they definitely bear Nervi’s signature didactic intent, but this may need a research trip back to the archives to confirm…
Among that debate’s participants was Matthys Levy, a structural engineering hero to any of us who were brought up on Structures for Architects, which he co-wrote with Mario Salvador. Levy joined us to walk us through the neighboring Hopkins Center, Dartmouth’s performing arts center designed by Harrison and Abramowitz around the same time as Leverone Field House was going up. While it’s best known as a sort of warmup project for that firm’s Lincoln Center, Levy talked us through the use of long-spanning barrel shells for the building’s main roof spans, and to point out a handful of details that show his interest in combining architectural form with structural logic. This one, for instance, is sort of a designer Rorschach test. Architects are likely to see it as a sequence of oval ceiling apertures, while engineers are more likely to see it as a series of swallowtail joists that spread out their collected shear across a wider cross section as they meet the carrying girder. That’s a Nervi touch, too, one that was best employed in the Manufattura Tabbachi in Bologna.
All in all an inspiring week. Back home now, digesting two solid conferences, following up with a bunch of new readings, and prepping for Fall studio, which will focus on a high rise multi-university center in Chicago’s South Loop…
July 14, 2018 § Leave a comment
A solid week of building science and technology history and geekery in Brussels, where the 6th International Congress on Construction History has just finished. After helping to organize 5ICCH in Chicago, this was the first Congress in a while where the Americans were able to relax and fully enjoy, and the range of papers, tours, and discussions was, as you’d expect, well worth the trip.
The field really does feel like it’s maturing, with the majority of the papers coming from graduate students or at least young faculty who are bringing energy, fresh ideas, and impressive findings with them. There were still plenty of familiar faces, but I was impressed at how many new names there were on the podium and in the audience–a sign that looking back at how our construction and engineering technologies have evolved over time is proving itself as a topic of inherent interest. It’s clear that there are distinct lines of inquiry–stone vaulting, history of contracting and administration, thin-shell concrete, skeletal iron, and vernacular building in general–that have formed consistent camps. All of these topics were well-represented, and some offered genuine fireworks. But there are also plenty of unexplored, or fresh finds as well. And new territories.
Belgium has been one of the most active centers of CH for a while, now, thanks to active programs at several universities–Antwerp, Leuven, and Brussels all participated in organizing the conference, and were all well represented by students and faculty giving papers. But it also proved to be a rich venue for examples of iron construction, infrastructure, timber roofs, etc.–all of which have large fan bases in the field. I played hooky one afternoon to get a walking tour of Victor Horta sites in, and was happily surprised at how technically rich much of his ‘ornamental’ ironwork is–Sullivanian in both its complexity and, once you see how it was done–its simplicity.
There were at least three highlights that will stick with me. The first was the buzz over a paper by Aleksandra Kosykh and Konrad Frommelt, done under the supervision of Werner Lorenz at Cottbus, that revealed an iron truss in the roof of the Marble Palace in St. Petersburg, Russia, from 1770–a decade or two earlier than any previously documented iron truss in France or anywhere else. Lorenz himself gave a similarly stunning keynote talk that summarized the project he’s had for the last dozen or so years on the lost bronze truss of the Pantheon’s portico roof, just in case anyone thought that the idea was born first in the 18th century. His research has ranged from digital reconstruction based on a demolition drawing by Borromini (!) to having local blacksmiths cold-hammer rivets made from the same bronze formula as the single known surviving rivet from the truss itself–and it’s shown definitively that Bernini did not, in fact, use the bronze for the baldacchino in St. Peter’s. (It went into cannons in the Castel Sant’Angelo, instead). The details will be published in an upcoming article in Construction History.
And, finally, the week’s last keynote was by Tullia Iori, of Roma Tre University, on the long research arc of the SIXXI program there, which is producing a comprehensive history of structural engineering in Italy during the twentieth century. The talk was partly an elegy for Sergio Poretti, who co-led the project until his sudden death last summer. The research that they and their students have produced has been insightful, the work they’ve studied almost universally beautiful, and the presentation heartfelt. Tullia and Sergio were two of the first scholars I met doing the Nervi research in Rome and they were enormously generous and helpful in steering Beauty’s Rigor. Sergio is much missed, but it was clear that SIXXI will continue to explore one of the field’s richest moments.
Heading to Boston next for IASS 2018. Conference season in full swing, but Brussels will be hard to top. Thanks to all the organizing staff and leaders of 6ICCH for a memorable and historic week.
June 26, 2018 § Leave a comment
I’ve been keeping out of trouble this last month with conference prep and a big digital project finishing up this week, but couldn’t let this one go. The above image is from SCB, of their proposed extension to Chicago’s Union Station. It’s had a pretty well-deserved thrashing in the press in the last 24 hours, but I think it’s worth piling on–if only to point out that the Station’s current stubby proportions were largely a result of its timing. Originally designed by D.H. Burnham & Co. in 1913–one of the last projects to enjoy Burnham’s attention before his death–it had a protracted construction history. Delayed by WWI, re-designed by Graham, Anderson, Probst, and White in 1921, and ultimately completed in 1927, a planned tower over its skylit waiting room never fully materialized, and was doomed once the Depression took hold. Its short, four-story office ‘tower’ is all that was ever built of a planned 16-story skyscraper that would have given the station a real presence on the West Loop skyline.
Or, really, not quite all that was ever built. Foundations were poured assuming that the skyscraper would be built, and so yesterday’s plan would take advantage of the substructure that’s already there–just not anywhere near the (ahem) somewhat more elegant proportions foreseen by GAPW: