July 29, 2015 § Leave a comment
Coast to coast…delighted to be in Norfolk, VA for a two week residency as the Virginia Design Medalist in Hanbury Evans Wright Vlattas’ offices. HEWV invites a scholar in each year to address issues in the profession, and they’ve asked me to help them brainstorm about the future of architecture…and of architects. As we’ve looked into our crystal balls, we’ve come up with four areas that are undergoing huge, productively disruptive change: design tools, materials and methods, organization and contractual relationships, and opportunities for engagement with social and urban networks. All of this is fascinating enough, but we’re basing our discussions on ‘parables’ from my historical research–after all, the introduction of steel and plate glass in Chicago construction was nothing short of massively disruptive.
This, of course, would be a great gig anywhere. But there’s this right down the street from the office…which we’re going to tour next week. Full report to follow, obvs…
July 25, 2015 § 1 Comment
St. Mary’s Cathedral, by Nervi and Pietro Belluschi. On the road, and by phone, so just these gorgeous images for the moment. But this one plays a key role in the book, as a bookend to Nervi’s career, a summation of the techniques he developed, and as a cautionary tale about working in new territories with unfamiliar problems to solve…
July 16, 2015 § 2 Comments
It’s author, Joseph Lstiburek, points out that Jeanne Gang’s Aqua Tower in Chicago very effectively mimics a fin-tube radiator, as each of its curved balconies very effectively radiates indoor air temperature to the exterior. The thermal image to the left shows, in Lstiburek’s words, “an 82-story heat exchanger” in the middle of Chicago.
This, of course, isn’t just Aqua’s problem, but the tower is certainly a paradigmatic example of thermal bridging. Concrete’s density makes it a thermally massive material, meaning it not only stores heat well, it also conducts heat well. Passive solar heating and ventilation, for instance, both rely on well-insulated thermal reservoirs of massive concrete to store heat–or the lack of it–that will dampen down the daily cycle of rapid heating and cooling of lighter building materials around them.
The problem with high rise construction is that concrete also offers a great work platform from which to assemble and install building cladding. Full curtain walls are draped outside of the building structure, but as you can see from a closeup of Aqua, a tall concrete frame suggests a much easier way to attach the building cladding–use single-story ‘storefront’ systems that just span between floor and ceiling slab at each story. This eases the structural issues that wind causes for fully hung curtain walls by limiting spans to a single floor height, and by providing robust connections at each slab. It also simplifies the labor involved in erecting cladding, since there is always easy access from the interior and since balconies can provide access (intermittently, in this case) from the outside face of the cladding.
The tradeoff, of course, is that if the slab is monolithic, it works as a very effective way to suck heat from one side of the cladding to the other. If, say, you’re trying to heat your condo during the winter, what you end up doing is heating the air in the room, which then heats the floor and ceiling slabs, which then–because they have so much outdoor surface in addition to their indoor area–try to heat the entire atmosphere.
There are, as Lstiburek points out, details that can reduce or eliminate this. By making a foam joint in the concrete and dramatically increasing the amount of rebar in the slab, you can essentially make a steel cantilever that’s wrapped in concrete–but concrete that isn’t continuous from inside to out. This is as expensive as it looks, of course, and it gives structural engineers fits, since they really want concrete to be as monolithic as it can be.
Aqua, it’s often pointed out, was a super-tightly budgeted project–basically a very standard (if very tall) condo tower with the one super-clever balcony detail that enabled its wave-like forms. There’s no chance that the developer didn’t do a full cost analysis on this balcony detail, and my guess is that this is evidence that we’re still really in a cheap-energy economy. It’s pretty clear that the least expensive way to deal with the thermal bridge issue in an 82-story residential tower is–still–to just throw more energy at the detail than can flow through it in a given day, to accept and pay for the losses through conduction while sitting inside (sorry, inside joke here) bathed in soft light and listening to Dionne Warwick in heart-warming stereo. Now, that may not be true fifty years from now, but that’s well past the developer’s involvement in the building, making this an economically-smart but legacy-dumb detail.
In fairness to Aqua, thermally-bridged concrete slabs have been the modus operandi for high-rise residential towers in Chicago since the 1920s. Flat slab construction has been the most spatially efficient way to squeeze as many floors into as little height as possible–not a great approach for commercial construction, which relies on the hollow spaces in steel-framed floors for duct runs, but perfect for residential construction where all of those ducts are replaced by thinner pipes feeding radiators. There is, sadly, no truth to the rumor that staff in Bertrand Goldberg’s office, located on the bottom floor of the raised office block in Marina City, had to wear winter boots during cold months to keep their feet from freezing on the concrete slab. But that’s as good an illustration as any of the problem.
Details like this are troubling, of course, to anyone concerned with how efficiently our buildings will operate over the next fifty years as energy costs and consequences soar. But to an historian, such details tend to reveal what the building culture of the time is actually responding to. In this case, it’s clear that despite what we know is coming, energy is still cheaper than the labor and the materials that would have been needed to make this a more efficient detail. I’ll leave the socio-political implications of that to the economists–to a developer that fact is a good piece of actionable data, but to humans in general it should be plenty sobering.
July 8, 2015 § Leave a comment
Piano’s building has been the subject of the kind of ecstatic, billowing buzz that any architect would dream of. In April, Michael Kimmelman of the Times wrote that
The new museum isn’t a masterpiece.
But it is a deft, serious achievement, a signal contribution to downtown and the city’s changing cultural landscape. Unlike so much big-name architecture, it’s not some weirdly shaped trophy building into which all the practical stuff of a working museum must be fitted.
June 25, 2015 § 3 Comments
That beautiful shot to the left there is from the basement of the Rookery, courtesy of CAF docent Claudia Winkler. On a recent basement tour their group noticed the sloping walls of the brick pier and wondered whether this was, in fact, one of the infamous pyramidal footings that supported many skyscrapers of the 1880s. Chicago Skyscrapers says otherwise–the Rookery is supported on grillage foundations. What gives?
Glad y’all asked, because this is an important problem in bearing foundation design. Above ground, engineers work hard to collect loads from floors and direct them into columns and piers. This is important, because the columns’ slenderness is the only thing that makes a skyscraper work–you can’t rent out structural area, so you have to find ways to condense loads from the floors above (two-dimensional) into elements that take up minimal floor space (columns are one-dimensional). All well and good, and there’s a good story about the “skeletalization” of brick structures into piers and then into wrought iron and eventually steel columns.
There’s a problem, though, when the columns get skinny. A skinny column can actually support a fair bit of weight, but the connection between the column and the floor is subject to all kinds of intense stresses as the floor loads are redirected into the column. In particular, the column wants to “punch” through the floor due to the shear inherent in the geometry of the problem. Think of pushing a pencil through cardboard–that’s what a thick, brick pier ‘feels’ like. If you try it with a nail, you can see the problem of a skinnier steel column.
That’s Mario Salvadori’s sketch of the problem, along with the most common solution. To prevent columns from punching through slabs, we typically try to maximize the (take a deep breath) interface area between the column and the slab. In other words, project the plan of the column through the depth of the slab. This is the area of material that will resist the shear forces at work–for a round column and a flat slab it will be a cylinder with the radius of the column and the depth of the slab. We can increase this area, and thus spread the stress out, by doing one of two things. We can make the slab deeper, which increases the height of the interface area (the height of the cylinder, e.g.) or we can increase the circumference of the column and thus the perimeter of the interface area.
Here’s how that was typically done in 1910s concrete construction. You can see that the top of each column has two ‘additions.’ There’s a ‘drop panel” that’s roughly square tucked up against the slab–this essentially makes the slab deeper around the column. And there’s a cone-shaped “mushroom cap” that spreads out the cross-sectional area of the column. Both of these are local modifications to the geometry of the slab or the column–they put additional depth or area only in the areas that they’re needed. As a result, the connection is able to spread the shear forces out over a much longer and deeper perimeter. Instead of the interface area being a cylinder whose surface area is the circumference of the column times the depth of the slab, it’s the area of a cylinder whose surface area is the circumference of the top of the cone and the depth of the drop panel. In other words, lots more.
Right, so what does this have to do with foundations?
Chicago engineers faced exactly the opposite of the slab problem below ground, in that they were trying to take the condensed loads in columns and spread them out over a wide area of clay soil–in other words, they were trying to turn the one-dimensional loads in the column back into the two-dimensional loads of the slab in order to distribute them from a point load (which would have sheared right through Chicago’s weak, wet clay) into an area load.
The solution–eventually–was to literally treat the foundation pads as a network of joists and beams just like the ironwork supporting the floors above. Here’s Birkmire’s drawing of a typical “grillage” foundation, (which in Chicago was often built of rejected steel rails, not the beams shown here). Steel’s bending capacity meant that the rails could easily take the bending loads (for those of you keeping score, these work like double cantilevers in reverse), but the punching shear remained a problem that was solved by the trapezoidal column base you can see between the column proper and the top row of steel beams. This is totally analogous to the mushroom caps above.
But before steel came in to the picture, engineers had to spread these loads out through materials–limestone and brick–that weren’t so good in bending. Thus the “pyramid” foundation, basically a big pile of rocks or bricks that very gradually spread the column loads out over the required area. The problems with these were twofold: they were heavy, which put even more load onto the poor soil below, and they took up room–either in the basement where service space for newfangled technologies like elevators and generators was becoming more and more important, or below the surface, which required extra excavation and therefore expense. The grillage foundation solved both of these.
So. The Rookery’s foundations are, absolutely, grillage foundations–here’s Engineering and Building Record reporting on the building’s completion in 1888:
The construction of the foundation is as follows: Under the pier is laid a homogeneous bed of concrete seventeen inches thick. On top of this steel rails are laid quite close together and about two feet shorter than the width of the foundation. On top of these rails is laid a second tier in the opposite direction but standing back at the sides about three feet each way. Above these is a third row of beams which is kept back to about the outer lines of the piers above on the sides though projecting on the ends; and finally there is a fourth row of beams which occupies a spaces a little larger than the area of the pier. These beams are bedded and surrounded with cement, and by reason of their being so thoroughly interlocked, form as it were a solid mass of steel enabling the foundations to spread out as quickly as they do without any defection of the beams, and thus spread the entire weight of the piers over the area of the lowest footing course.”
So what’s going on above? The Rookery is a hybrid structure–most of its structure consists of iron columns but there are also four massive cores that housed the building’s fireproof safe deposit boxes in the corners of the courtyard. I’m guessing that the picture above was taken at the base of one of these, where the masonry pier has to be supported on steel grillage foundations. If that’s the case, it would make sense that the “column base” for the walls would actually be made out of brick, spreading the (really heavy) loads of these four cores out over the steel grills below. You can see that the shape of the brick “spread” in Claudia’s photograph is pretty close to the shape of the column cap in Birkmire’s drawing.
But it was also common for (expensive) iron columns to sit on (cheaper) brick piers in basements, where even if space was at a premium it certainly wasn’t as valuable as the space on the rental floors above–so this could also be a brick pier supporting iron columns above and resting on iron or steel grills below. This would also explain the “column base.”
Either way, punching shear remains an issue that engineers deal with all the time. It’s easier to handle today with high-strength reinforcing steel, but you can still see evidence of this issue in slabs with drop panels, waffle slabs that are filled in around column supports, and in concrete girders that get just a bit deeper as they approach columns. Even Nervi found ways to cope with the problem…rather elegantly:
June 11, 2015 § 2 Comments
Still slightly abuzz from last week…in addition to the Congress, we got to see a major stretch of the Riverwalk open to pedestrian traffic and Henry Ives Cobb’s 1895 Chicago Athletic Club open as the city’s latest chicest hotel (it looks amazing).
But we did just miss what might be the best thing to happen to joggers, bikers, and pedestrians of all types on the north side. The 606, the city’s answer to New York’s High Line, opened just as we were finishing things up on Sunday. Using an old elevated freight railway (about 3 of 46 miles of elevated, grade-crossing-free track constructed in the early 20th century), the city has built a linear park that does a nice transect from west of Milwaukee Avenue all the way to the lakefront. And, sure enough, here’s cyclist and hyperlapse cinematographer Steven Vance recording the entire thing:
Can’t wait to get back and try this out…
June 8, 2015 § Leave a comment
Well, it’s not exactly the UN, but that is Construction History royalty there, debating the future of the field at our Scientific Committee lunch this week. Five triennial meetings along, the international field seems to have some momentum, but as Santiago Huerta pointed out in his closing keynote, any pure historical research in these days of vanishing funding and tight budgets is a challenge.
All the more reason to appreciate the roughly 300 delegates who showed up, from points as far afield as Japan, Brazil, Turkey, and the Near North Side. The city cooperated, with exactly one June rainstorm the entire week, and cool weather for walking tours on Friday–we showed off Mies, Frank Lloyd Wright, the River’s bridges, downtown skyscrapers, two construction sites, and as mentioned earlier a brilliant canopy tour of 1890s terra cotta being restored. I got to show off skyscraper history with WJE preservation engineer Ed Gerns, a rare treat for me and (I hope) informative for a good crowd of 30 or so.
Our keynotes were spectacular–UCLA’s Stella Nair on ‘experimental archaeology’ in South America that tries to understand how stone carving techniques enabled massive construction there, James Campbell on libraries, brick, and staircases, Santiago’s stocktaking on the discipline, and SOM”s Bill Baker on whether or not Frank Lloyd Wright’s Mile High Tower would have been feasible or not (spoiler alert: not). Baker’s talk was followed by a reception at SOM’s Chicago office, really one of the week’s highlights as they put out a huge range of models and drawings for us to gawk at over our wine and canapes. And SOM’s generosity was matched by the Builder’s Association of Chicago, which sponsored a cocktail evening and presentations by the leaders of some of the city’s longest-lived family contracting firms–a genuinely historic evening and great to see international historians mingling with some of the city’s biggest construction names (thanks especially to Mary Brush of Brush Architects for organizing this…)
And, plenty of good paper sessions. The range of topics at these Congresses gets more and more astonishing every time, and there are always happy surprises. The history of thermal insulation in postwar Belgium? Sure thing–and absolutely fascinating. Dante Bini’s pneumatic concrete formwork, which built a vacation home for Michelangelo Antonioni, among others? Astonishing (and, frankly, mystifying…I still can’t figure out how these actually stood up). Contracting in India in the 1950s, the construction process of Lina Bo Bardi’s Sao Paolo Museum of Art (on the bucket list), and George Romney’s role in HUD’s “Operation Breakthrough” housing initiative in the 1970s? Those were all in one session…And that’s just what I managed to attend. With six parallel sessions each day, the range and number of papers were frankly daunting.
And we did manage to get out of the Palmer House once or twice. Here’s my Iowa State colleague Rob Whitehead and I treating keynote speaker James Campbell and his Cambridge University colleague to an elegant meal at one of the city’s finer dining establishments–Bucktown’s Arturo’s Tacos. We like to treat our international guests properly.
It was about eight years ago that the founding CHSA membership–Brian Bowen, John Ochsendorf, Don Friedman, and I first mentioned hosting the International Congress in the U.S. Chicago was the only city we ever even considered, and the process of organizing and putting this on has been more of a joy than any of us might admit. We treated ourselves to one final, celebratory lunch on the way out of town, toasting our Congress manager Melanie Feerst for her tireless work to actually get things organized and in place. We have a huge list of people to thank–a local organizing committee that made hundreds of delegates feel absolutely welcome in Chicago, the Chicago Architecture Foundation for helping organize some of our tours, a scientific committee that reviewed over 500 abstracts, local volunteers, sponsors, and of course attendees who were willing to fly thousands of miles to take part in the discussions.
Santiago is right that it’s an uphill battle to keep an admittedly abstruse discipline going these days, but it’s hard not to be optimistic after a week like this. The number of students, young faculty, and professionals who put together great research and great stories all left us feeling like there remains plenty of promise in CH.
Next year, the American branch will have its biennial meeting in Austin, Texas in May. And at the conference’s close we were thrilled to announce that 6ICCH will be held in 2018 in Brussels. See many of you there…!