notre dame–some background

April 15, 2019 § Leave a comment

The news that Notre Dame Cathedral in Paris is on fire has come with an understandable uncertainty and concern about the demise of the entire structure. There are a couple of key points that haven’t yet made any of the major news coverage that are worth pointing out…

What’s been burning the last couple of hours is the timber roof that had rested on top of the cathedral’s stone vaults. Initial reports are that there was renovation being done in the structure’s attic, which makes sense given the presence of scaffolding in much of the footage, and it’s possible/likely that this activity led to the blaze. At least some of the roof, including the spire that collapsed, was actually part of the 19th century ‘restoration’ by Viollet-le-Duc. Its loss is catastrophic, but it would not be the first cathedral roof to be destroyed by fire–Rheims’ timber roof was destroyed in a conflagration caused by shelling during WWI.

Scientific American, August, 1926

That incident may provide some modest hope. Reims’ stone vaulting survived the shelling, though it was heavily damaged. The lost roof over Notre Dame, like those of the other great cathedrals, was primarily a weather covering, to keep rain and snow off of the vulnerable limestone vaults and mortar that form the main spaces of the cathedral below. It wasn’t structural, in that the vaults, piers, and flying buttresses that structure and surround those spaces below have functioned as support on their own–and, in fact, one of the major structural problems with gothic vaults was absorbing the thrust from the pitched timber roofs above them.

All of that structure–what we think of as the space of the cathedral–is stone, which doesn’t burn. So those news reports that have breathlessly reported on the ‘spread’ of the fire to these elements don’t have things quite right. Limestone does calcine and deteriorate under high heat, and the fragile vaults are vulnerable to falling debris from the burning roof. The quantity of water being used to extinguish the fire is, too, potentially damaging. So collapse is a real danger, but not necessarily inevitable.

Three possible outcomes. One, like Rheims, the cathedral could survive the roof’s burning damaged but intact, requiring a new roof (probably of lighter lumber or metal–like the repair of Reims) and repair to damaged but surviving vaults below. Two, falling timbers and the spire may have collapsed significant portions of the vaults below, which would require extensive new structural work involving scaffolding and years of craft-intensive labor. The collapse of choir vaults at Beauvais in 1284 was devastating but only partial. The worst case would involve weakened stone and mortar from the heat of the fire and the water from attempts to extinguish it and a broader collapse. If, for instance, the main towers were compromised, their ‘bookend’ effect on the vaults behind them would leave the nave without adequate buttressing in the long direction.

Update 7:45pm: From the first images of the interior it looks like at least one vault has partially collapsed, but most of the structure remained intact:

We’re getting to see some of the first images from inside Notre Dame Cathedral. President Macron: “‘I say to you very solemnly this evening, this cathedral will be rebuilt.”— Jim Roberts (@nycjim) April 15, 2019


ponte morandi demolition

April 4, 2019 § Leave a comment


Stunning footage of the surviving spans of Genoa’s Ponte Morandi being gently demolished and hauled off, via La Repubblica on line today.  Seeing the viaduct portions standing alone on their point-supported piers is particularly eerie, and there are rare  lessons throughout–sad ones, albeit–on structural form and shape.

john hancock on WBEZ’s Curious City

March 24, 2019 § Leave a comment

hancock sofitelWBEZ’s Curious City is a brilliant segment that answers listener’s questions about Chicago–if you want to know why steak and lemonade is a thing, or are curious about why certain street names are pronounced the way they are,  they’ve got your back.  Warning: the archive is addictive.

This week they cover the history of the John Hancock Tower (I know, 875 North Michigan is its official title, but come on).  I was happy to throw in some thoughts about why you’d build a 100-story building a mile north of the Loop in the 1960s, how a hollow tube structure helped it become the most efficient tall building on the planet, and how one tall building can be better than two shorter ones.  They also speak with Yasmin Khan, Fazlur’s daughter and also a structural engineer, about Khan’s career and his inspiring but far too short career with SOM.  Her story about her father quietly lurking on north Michigan Avenue to hear passers-by talk about the Hancock is worth a listen on its own.

UPDATE:  There’s a video version, too..

first skyscrapers panel at 10th CTBUH world congress

March 5, 2019 § Leave a comment

Figure 04

Not this one.

Oh, this is going to be good.  CTBUH has announced that, as part of its 10th World Congress next year in Chicago, it will host a symposium on “first skyscrapers.”  I’ve been part of a consultant team that’s helped them formulate the discussion–they’ve wisely decided to open it up to a Call for Abstracts, inviting anyone with a theory on how the term should be defined (or not) and/or what we should think about when claiming any tall building as a ‘first.’

From the call:

CTBUH is thus issuing a Call for Abstracts to all scholars of history and colleagues with an expertise in this field (including architecture, architectural history, construction, economics, engineering, and beyond) to answer the prompt, “What skyscraper could be considered a ‘first’ in a particular technological field or other dimension?” and to state upon what criteria this assertion is based.

More information on the symposium, and the official Call for Abstracts, here:

Deadline is 26 March, abstract length limited to 300 words.  Regular readers may have some idea of what I’m going to propose…and how tough it’s going to be for me to limit myself to that.

Start your engines…

sutherland lecture online

February 22, 2019 § Leave a comment

Very pleased to note that the Institution of Structural Engineers in London has uploaded video of the James Sutherland History Lecture that I was invited to give earlier this month there.  On “Pier Luigi Nervi and the Role of Structure in Architectural Beauty,” anyone who’s seen me talk on Nervi will be familiar with the first half, but there are some newly jotted-down thoughts toward the end that are fresher.  Many thanks to Rachel Doran, Jane Entwistle, Andrew Smith, et al for putting on such a fine evening…



February 21, 2019 § Leave a comment

Tyler Vincent

Tyler Vincent

What would gothic cathedrals have looked like if the groin vault had, like concrete, been lost as a technology at the end of the Roman Empire?  That was last week’s discussion question in my Big and Tall seminar, and the class responded with some intriguing possibilities.

The alternate history has been a go-to question in the course since I started teaching it, since it highlights the evolutionary nature of building.  Developments such as the groin vault, or wrought iron, or plate glass, all solved individual problems, but there would, undoubtedly, have been work-arounds that would have produced viable buildings solving functional issues in other ways.  (Somewhere, in an alternate universe, a Big and Tall course is wondering whether humans would have built sky-dwellings without the discovery of Unobtanium.  Submit your answers in the comments below).

Phil Hess

Phil Hess

Lots of good thoughts, including souped-up barrel vaults like those above.  In the first case the assumption is that the flying buttress still develops, but it turns into a thicker element that can absorb more of the distributed thrust of the barrel vault, instead of just taking the point loads of a groin vault.  The solution just above uses barrel vaults to thrust against one another (or, at least, against the supporting walls), and cleverly steps them down toward the ground to create a pyramid of perpendicular buttressing.

Obishek Mandal

Obishek Mandal

Less spectacular but perhaps more viable, a number of solutions involved more elaborate timber structures, trusses that adopted the pointed arch (imported from the middle east via Norman conquest and diffusion through the Mediterranean) and the availability of heavy timber in northern Europe.  This makes perfect sense–if the groin vault never develops, just don’t build the groin vaults, but let the truss work that supports the tall timber roof express itself to the nave below.

Jeffrey Klynsma

Jeffrey Klynsma

OR, build simple trusses over masonry walls, but then find a way to build the Aya Sophia’s dome over the crossing–focusing your constructive energy on the church’s most sacred point.  I like this one a lot–even though it would have been asking quite a bit of medieval carpenters to figure out that junction between dome and truss (something, let’s face it, that even Palladio couldn’t quite handle).

Thanks to Tyler Vincent, Jeffrey Klynsma, Obishek Mandal, and Phil Hess for some particularly striking suggestions.  More alt-SciTech when we hit the age of iron…

cathedrals of a sort + poetics

February 6, 2019 § 2 Comments

(Warning: somewhat hifalutin’.)

Subtly different vibe this week. In London for a pair of lectures, one organized by the good folks at Foster + Partners, my old stomping grounds, and the other the James Sutherland Lecture to the Institution of Structural Engineers, the latter an event that honors a truly great historian of engineering with an annual talk on an historic subject.

Both talks were on the Nervi book, with slightly varying takes. Nervi was, of course a name that floated around the studios at Foster’s often, and the links between fabrication, structural performance, and assembly certainly live on in that firm’s work. There’s a natural interest in the constraints faced by him as a builder, and also in the geometries that proved to be a link between the structural forms his engineering demanded and the largely unskilled labor force that his contracting firm had at its disposal. Break the problem down into a long series of repetitive, manageable tasks, and you can build for less than your competitors.

In my talk to the ISE, I expanded on this a bit. Nervi was always described as a “poet in concrete,” and I’ve gotten a fair bit of mileage out of showing how, far from the airy niceties of poetry, Nervi’s career was based in the muddy realities of job sites and fabrication yards. But the results are, of course, uncannily ‘poetic,’ and being mildly interested in such things I tried to show that, rather than that description making us think differently about Nervi, it might make us think differently about poetry. We often use the term as a shorthand for anything that strikes us emotionally, but even a short delve into debates over what poetry really is takes you to discussions about form, meter, rhythm, and rules. Common definitions talk about emotional content being distilled into rigorously developed forms–sonnets, e.g.–that require the poet not only to express an emotion or sensibility, but to do so within an intentionally limiting set of constraints.

Well, now.

Nervi’s best work does exactly that. His structural shapes, like those of many of his contemporaries, are breathtaking leaps, but they’re inevitably achieved within a tight set of restrictions–economic ones, of course, but also material, labor, schedule, etc.–that refined those shapes into patterns and rhythms that relate to a very different set of rules than the pure structural ones with which he’s most commonly associated. Constraint creates design, as the Eames’ said. It’s to be embraced, not bemoaned. Working this up into a larger paper for the ISE’s Journal, but this seems to me what separates Nervi’s shells from other contemporaries–their realization is filtered through the limited means Nervi had, and this dialogue between structural ambition and the difficult circumstances of the job site is imprinted in the roof forms themselves–patterns that Nervi recognized as visually important and worth celebrating.

What poet, after all, complains about the number of syllables in a haiku?

As you can see, I managed to get out for a day or two as well. London cooperated with a gorgeous Sunday, and I took the opportunity to see Richard Turner’s Palm House at Kew, a wrought-iron and glass cathedral that is a foundational text of sorts. Cluttered up with plants, of course, but still compelling almost 170 years after it was built. The trick of a single radius throughout is another example of how functional ambitions–structural and solar, in this case–get filtered through the constraints of, in this case, bending metal to consistent shapes. Build one jig and use it to bend every single framing member and every piece of glass in the entire structure, and you’ve saved a considerable amount on fabrication–in addition to which you’ve broken down the process of making the building into repetitive, relatively simple tasks that remove the expensive, skilled labor (building the jig) from the bulk of the work (heating up the iron members and bending them around said jig). The result, if not wholly poetic, is nevertheless compelling, especially on a sunny February afternoon.

As is this one, which is another story about structure and fabrication altogether:

Thanks to all, esp. ace ISU alum Kristi, for the invites and logistical help.

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