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…