5

STRUCTURE

 

The most prominent features of ancient Greek temples are the columns. Made out of massive superimposed stone drums, their surface carved with shallow grooves, or flutes, the columns resemble soldiers at attention, the sharp vertical shadows suggesting the folds of a Greek chiton, or tunic. A classical column has a gentle swelling, an unevenly tapered profile called entasis, which means “stretching tightly” in Greek, as if the column was straining to support its load—another human reference. The entablature that spans between the columns is composed of elaborately carved parts, each with its distinctive form and name. A Doric frieze, for example, is made up of alternating triglyphs—stylized beam ends—and metopes, square panels that are sometimes adorned with bas-reliefs. The cornice above the frieze contains brackets decorated with guttae, or “drops,” an architectural trope for the blood that ran from the sacrificial altar. Except for their wooden rafters and clay-tile roofs, Greek temples were built entirely of white Pentelic marble. Assembled without mortar, and with only occasional bronze centering pins and lead clamps, these monolithic buildings have long been considered the purest expression of structure transformed into architecture.

When the twenty-four-year-old Charles-Édouard Jeanneret, not yet renamed Le Corbusier, visited Athens in September 1911, he spent three weeks on the Acropolis, sketching the ruins. The Parthenon overwhelmed him. “Never in my life have I experienced the subtleties of such monochromy,” he wrote in his travel diary.1 “The body, the mind, the heart gasp, suddenly overpowered.” While there, Charles-Édouard experienced a sort of epiphany: “The hours spent in those silent sanctuaries inspired in me a youthful courage and the true desire to become an honorable builder.”

Witold Rybczynski, Propylaea seen from Parthenon, July 11, 1964

The walls of Le Corbusier’s early villas are uniformly painted white, and the columns are always round, although lacking flutes and entasis. He worked hard to achieve the monolithic simplicity of ancient Greek architecture and the “subtleties of monochromy,” and like temple ruins his buildings appear to be constructed of one solid material. This illusion required considerable effort. Modernist architects used ribbon windows in lieu of openings punched into the wall, and since in the Villa Savoye these windows stretch across the entire façade, the reinforced concrete lintels are so long that they are actually suspended from the roof slab above. None of this complicated structure is visible, however, since the concrete and masonry are plastered over and painted to create the smooth, uniform surface that the architect desired.

Le Corbusier remained highly selective about revealing what made his buildings stand up. His famous apartment building in Marseilles, the Unité d’Habitation, was raised off the ground on massive piers that Lewis Mumford described as “cyclopean” when he visited the building. “[Le Corbusier] has used concrete for all it is worth as a sculptural form,” Mumford wrote, “emphasizing and even exaggerating its plastic qualities, to the extent of leaving untouched the evidences of crude, sometimes inept workmanship.” Although the hollow piers are structural, most of the visible concrete is not, and the largely hidden structure of the building is a mixture of cast-in-place concrete, precast concrete, and steel framing. Thus, while the Unité d’Habitation popularized the use of rough concrete, or béton brut, giving rise to the term Brutalism, its construction is actually a hybrid.

Two examples from the 1940s show how, contrary to Le Corbusier, some architects went to great lengths to make known the structure of their buildings. At the Illinois Institute of Technology, Mies van der Rohe designed a series of low buildings consisting of steel frames with brick and glass infill. The actual structural steel was encased in concrete to meet fire codes, so Mies added nonstructural I-beams and channels on the exterior to “express” the hidden columns and beams. In the Equitable Savings and Loan Association Building in Portland, Oregon, Pietro Belluschi—another European immigrant—likewise expressed the structure, in this case a reinforced-concrete frame. He filled the space between the floor slabs with sea-green tinted glass and dark cast-aluminum panels, and covered the grid of concrete columns and beams with contrasting silver aluminum. Like Mies, Belluschi wanted the structure to—as much as possible—be the architecture.

Pietro Belluschi, Equitable Building, Portland, Oregon, 1948

Architects have always had to decide how to deal with structure: express it or ignore it, display it or hide it, play it up or play it down. The decision depends on the materials and techniques available, and on the engineering know-how of the time, but the choice also depends on the architect’s intentions. Some architects care deeply about an “honest” representation of how a building is built and reveal the structure, which complicates life for the builder, since what looks simple is often difficult to construct. When columns and beams cannot be revealed, architects like Mies and Belluschi resort to a sort of faux structure. Others choose to conceal structural members altogether, for the sake of dramatic visual effects. I once saw a stair whose treads magically cantilevered out of a wall; the architect, Moshe Safdie, explained that hidden inside the wall was a framework of heavy steel members to which the treads were welded. Another architect might have revealed how the treads were supported, as Aalto did in the Villa Mairea, where exposed steel I-beams carry the treads, or he might make the stair entirely self-supporting, as Jack Diamond did in a dramatic all-glass stair in the Four Seasons Centre for the Performing Arts.

THEORIES OF CONSTRUCTION

“An architect cannot construct a building without a theory of construction, however simple-minded that theory might be,” writes the architectural historian Edward R. Ford.

Construction is not mathematics; architectural construction is just as subjective a process as is architectural design. Construction involves a more complex set of concerns, the application of scientific laws, and a tradition (or perhaps a conventional wisdom) as to how things ought to be built, but that tradition and that wisdom are no more or less valid than the tradition or conventional wisdom as to how buildings should appear.

In other words, there are many ways of building, ways that are more or less beautiful, more or less dramatic, more or less evident, and, of course, more or less expensive. I once designed a house using conventional wood-frame construction. Since the spans were short, it was easy to calculate the size of the floor joists, but there was one large space that required a special beam, and I turned to an engineer friend for advice. “Do you want it cheap, or architectural?” Emmanuel Leon asked me. Since this tall room was the main living space of the house, I chose the latter, and he designed a striking upside-down king-post truss, with cables as tension members.

Ludwig Mies van der Rohe, Farnsworth House, Plano, Illinois, 1951

Mies’s solutions were always architectural. Although fire regulations prevented him from exposing steel in large buildings, he was able to do so in a private residence such as the Farnsworth House. The external columns are eight-inch-deep steel I-beams carrying fifteen-inch steel channels that support the floor and roof.2 Although the columns and channels are exposed, the way they are attached—by a plug weld on the back of the column flange—is concealed from view. The I-beams that span the width of the house and support precast concrete roof planks are likewise hidden behind a suspended plaster ceiling. As Ford writes, Mies “preferred, in later life, to expose the steel, but he would accept concealment if required,” a theory of construction that is nothing if not pragmatic.

In the late 1920s, Frank Lloyd Wright wrote a famous series of essays, “The Meaning of Materials,” arguing that “each material has its own message and, to the creative artist, its own song.” It’s a compelling metaphor, but in practice Wright was as pragmatic as Mies, sometimes revealing the “song,” often muting it. The most striking feature of the Robie House in Chicago, for example, is a dramatic twenty-foot roof cantilever—an unprecedented dimension for wood construction. What makes this cantilever possible is that the wooden rafters rest on concealed steel beams. As for the “floating” balconies and roofs that appear to be carried by heavy brick piers, they are also supported by a hidden steel frame. In this house, steel is not allowed to sing.

Wright often exposed concrete, although he recognized that it is not a particularly attractive material. “As an artificial stone, concrete has no great, certainly no independent, aesthetic value whatsoever,” he wrote. “As a plastic material—eventually becoming stone-like in character—there lives in it great aesthetic property, as yet inadequately expressed.” At the time that he wrote this, he had already used exposed concrete in the Unity Temple in Oak Park, and in the four Los Angeles textile-block houses. But none of these projects exploits the unique properties of reinforced concrete as dramatically as Fallingwater. The terraces, parapets, eaves, and balustrades form one continuous, monolithic piece of poured-in-place concrete. Wright is not interested in revealing the structure, however. All the concrete is uniformly plastered over and painted. The four large girders that support the terrace over the stream are concealed behind a flat soffit. The girders are supported by three exposed concrete brackets, but these are seen only from the stair that descends to the water; the fourth bracket, which is visible from the exterior, is made out of stone rather than concrete. Elsewhere, the supports of the upper terrace are disguised as window mullions to further the illusion of weightlessness.

Frank Lloyd Wright, Robie House, Chicago, 1909

Fallingwater is a combination of concrete, steel, and stone, while the Guggenheim Museum is built entirely of reinforced concrete. As in Fallingwater, the plastered and painted concrete surfaces are continuous, so it is impossible to distinguish what is structural and what is merely infill. The balustrade, for example, stiffens the spiraling ramp; the twelve ribs from which the ramp cantilevers look like walls and at the top turn into supports for the glass dome that covers the atrium. The curved ramp has a bulging bay on each floor—does it help to support the ramp? Impossible to tell. “As an object by itself, the Guggenheim Museum interior is, like the exterior, a remarkable example of abstract sculpture,” wrote Lewis Mumford in a New Yorker review. “Without ornament, without texture, without positive color, in a design as smoothly cylindrical as a figure by Fernand Léger—this is how Wright shows himself here a master of the abstract resources of modern form.” That was written in 1959, when the idea that a building could be a work of sculpture rather than a work of construction was still a novelty. Thirty years later, as we shall see, that would no longer be the case.

EXPOSING THE BONES

The great pioneer of concrete, the French architect Auguste Perret, once observed that “architecture is what makes beautiful ruins.” Louis Kahn took this dictum to heart, and more than any other modern architect he was obsessed by the idea of revealing the main supporting elements of a building, as if what remained when a building fell into ruin was architecture’s true soul. This attitude was undoubtedly influenced by his visits to ancient sites such as the Parthenon, which he saw when he was forty-nine, just before he designed the Yale Art Gallery and embarked on the most creative phase of his illustrious but short career.

Kahn believed that how a building was constructed should be clearly visible, without subterfuge or artifice. For this reason, he favored walls that were monolithic—that is, solid concrete or solid brick. However, modern construction is layered—what looks like a solid brick wall consists of a thin brick veneer, an air space, a vapor barrier, insulation, a backup wall, and the interior finish. This reality made Kahn’s preference for “honest” construction hard to achieve. The exposed concrete space-frame ceiling of the Yale Art Gallery is visually striking but has no structural logic. “Kahn’s structure uses a massive quantity of concrete in a complex arrangement to achieve what is ultimately not a particularly impressive span,” writes Edward Ford. The precast concrete beams of the Richards Medical Building effectively reveal how the floors are supported but are needlessly complicated and expensive to build. When Kahn’s friend Eero Saarinen saw the Richards Building, he asked, “Lou, do you consider this building an architectural or a structural success?” Saarinen, who had designed research laboratories for General Motors, IBM, and Bell Telephone, was implying that the structure compromised the function—which it did. Although the exposed structural system is visually striking, the large areas of glass create glare, and the dust from the exposed concrete compromises the laboratories.

Louis I. Kahn, Section, Phillips Exeter Academy Library, Exeter, New Hampshire, 1972

In a library for Phillips Exeter Academy, Kahn came close to designing a building that straightforwardly expresses its construction. The eight-story library resembles a square doughnut. The architectural concept is extremely simple: the doughnut consists of two rings, the outer ring contains study carrels, while the inner ring houses the book stacks; the “hole” is an atrium lit by a large skylight. Initially the building was to be all brick, but to save money Kahn built the stacks of reinforced concrete, and the hybrid result is an evocative example of his approach to structure. “I felt the striving not for severity but for the purity that I sense in a Greek temple,” Kahn said of the library. That purity is visible in the two construction systems: reinforced concrete columns, beams, and slabs for the heavy book stacks, and brick piers and arches for the carrels.

The plasticity of poured-in-place concrete, which Kahn called “molten stone,” is expressed by huge circles cut out of the four walls that enclose the library atrium. The joints of the formwork are everywhere clearly visible, since the concrete is exposed. The surface is marked by a regular pattern of small circular recesses, a detail that Kahn developed at the Salk Institute. Cast-in-place concrete requires wire ties to keep the forms from being pushed apart when the heavy mix is poured in; after the concrete has set, the ends of the ties are snipped off and the concrete is patched to prevent the wire from rusting. Kahn designed a neat recessed lead plug to replace the unsightly patch. The regular pattern of plugs was a kind of decoration, and, equally important to Kahn, the plug revealed how the wall was made.

Ford calls the Exeter library “the purest of Kahn’s brick structures.” The openings in the brick façade are spanned by traditional jack arches, flat arches made out of radially sawn bricks. However, the exterior walls are less solid than they appear. Kahn was sometimes able to use solid brick walls—in India and Bangladesh—but in America, labor costs and the need to accommodate insulation mandated a cavity wall. The library wall is actually two layers (with a cavity and insulation between them): a twelve-inch structural bearing wall made out of brick and cement block, and an inner veneer of brick that is only four inches thick. There is a small detail that few will notice. The exterior wall includes a line of header bricks every eight courses to bind the bricks and blocks together, while the inner wall, being a veneer, has no headers. This attitude differentiates the architect from the stage designer; the former works to satisfy his own constructional logic, while the latter is concerned only with the view from the seats.

Louis I. Kahn, Phillips Exeter Academy Library, Exeter, New Hampshire, 1972

Renzo Piano worked briefly in Kahn’s office. While Kahn used mainly masonry and concrete, and Piano’s structures are generally steel, Kahn’s attitude to construction clearly had an influence on the young Italian. Piano’s first high-profile commission, the Centre Pompidou, the result of a competition he entered with Richard Rogers, revels in its construction. The main columns are thirty-four-inch-diameter steel masts; steel trusses span one hundred and fifty feet, the entire width of the building; tension rods provide lateral bracing; and escalators and services are suspended from cast steel gerberettes—cantilevered brackets that recall Victorian cast ironwork. The steel in the building is exposed throughout, and fireproofed either by water cooling (in the case of the water-filled masts) or by mineral-wool heat shields covered by stainless steel (in the case of the trusses). A third fire-protection technique involves coating the steel with an intumescent material that expands during a fire to produce a light char that retards the transfer of heat. Since this coating is as thin as paint, it allows the connection details to be plainly visible. And there is much to reveal. “Everything in the structure is articulated,” wrote Ted Happold, an engineer who was a member of the design team. “Every detail shows how the building has been looked upon as a framed mechanism.”

Renzo Piano & Richard Rogers, Centre Pompidou, Paris, 1977

A decade after the Centre Pompidou opened, Norman Foster completed the Hongkong and Shanghai Bank, whose planning likewise stresses flexibility and adaptability by providing large column-free spaces. Large spans inevitably provide an opportunity to dramatize the structures. Foster and Rogers had been partners, and Foster treated the structure of the bank with equal daring. Most high-rise office buildings are supported by columns that carry loads down to the ground, but Foster opted for a different solution, suspending the floors from intermittent bridge-like trusses. The trusses and columns on the exterior of the building are exposed and are a visual explanation of how the forty-seven-story tower is built.

Foster + Partners, Hongkong and Shanghai Bank, Hong Kong, 1986

The Centre Pompidou and the Hongkong Bank dramatically reveal their long-span structure. Did these two buildings herald a new approach to construction? Not exactly. For one thing, many architects are uninterested in featuring structure. For another, exposing columns and trusses on the exterior of a building is expensive, in terms of both construction and maintenance. Moreover, few buildings require the high degree of flexibility achieved by extremely long spans. Where long-span structures really shine is in airport terminals, which require large spaces that can accommodate the ever-changing mix of ticketing counters, screening areas, and shops. Foster, Rogers, and Piano have designed striking terminals in Britain, Spain, China, and Japan, whose chief architectural feature is dramatic structure, and which achieve the modernist dream of revealing—not simply expressing—the bones of a building.

LAYERS

While generations of architects have admired the Acropolis, its structural purity is atypical; most ancient buildings were more complicated, especially after the Romans invented hydraulic cement. This material used volcanic dust (pozzolana) or gypsum and lime as binders, and enabled builders to make a crude sort of concrete that could be cast into vaults and domes. Since the surface of concrete is unattractive, it was generally covered by a layer of marble or brick, making the “honest” expression of structure difficult.3 The Coliseum, for example, is cast-in-place concrete faced in brick on the interior and travertine marble on the exterior. The prominent attached half-columns carry no loads, nor are they even an expression of the structure, since the floors of the amphitheater are supported by arches and vaults, rather than by columns and beams.

The Coliseum was completed in A.D. 80, and fifty years later the Romans built another impressive concrete building: the Pantheon. The dome is more than 140 feet in diameter, a tapered shell that is 21 feet thick at the base and 4 feet thick at the top. The exposed concrete coffers of the interior reduce the weight of the dome. The thick concrete wall that carries the dome on brick relieving arches is sheathed in marble on the inside and brick on the outside. The forty-foot columns that support the portico represent an older technology, being made out of single pieces of granite five feet in diameter. Monoliths, indeed.

Thomas Ustick Walter, dome of U.S. Capitol, Washington, D.C., 1859

Nowhere is the discrepancy between appearance and reality more pronounced than in the construction of domes. The horizontal thrust of Brunelleschi’s octagonal brick dome of the cathedral of Florence is taken by concealed reinforcement—four rings of sandstone and iron, and one of wood. The dome itself consists of two independent shells; an external nonstructural shell that supports the roofing tiles, and an internal shell that does all the structural work. The dome of Christopher Wren’s St. Paul’s Cathedral has no fewer than three shells: an inner plastered-brick dome, a timber-framed outer dome, and between them a brick cone that supports both the outer dome and the heavy stone lantern.

Like Brunelleschi, Wren was a pragmatist—for him construction was merely a means to an end. His particular architectural problem was to create a landmark that would be visible throughout the city, a replacement for the tall Gothic spire of the old St. Paul’s Cathedral, which had been destroyed in the Great Fire. As a classicist, he wanted a dome, and for additional height he added the seventy-five-foot lantern. The inner dome is hemispherical and much lower, and like the Pantheon has an oculus to light the interior. Wren’s assistant Robert Hooke, likewise a philosopher, architect, and polymath, devised the method of counteracting the outward thrust of the dome, which Wren described: “Altho’ the Dome wants no Butment, yet, for greater Caution, it is hooped with Iron in this Manner; a Chanel is cut in the Bandage of Portland-stone, in which is laid a double Chain of Iron strongly linked together at every ten Feet, and the whole Chanel filled up with Lead.” The vital chain, like the arched buttresses that brace the masonry cone, was invisible—it was required “for greater Caution,” but not required to be seen. Thomas Ustick Walter’s dome of the U.S. Capitol likewise consists of three shells, with an inner dome made of cast iron, although you would hardly know this looking at the classical exterior, a reminder that there is no rule that construction must take precedence.

THE PILASTER IS A LIE

At the end of the Renaissance, architects such as Michelangelo and Giulio Romano consciously distorted classical motifs, making what had ossified into a canon once more fresh—that is, making what was familiar unfamiliar. The distortions included irregular column spacing, “dropped” keystones, “broken” pediments, columns with alternating “uncut” drums, and artificially “rusticated” stonework. What was later christened mannerism broke the rules, but it also depended on them, for, as Venturi writes in his classic Complexity and Contradiction in Architecture, “convention, system, order, genericness, manners, must be there in the first place before they can be broken.”

Venturi’s mannerist leanings are evident in the hybrid construction of the Sainsbury Wing of the National Gallery. The floors are cast-in-place concrete supported by irregularly spaced columns that carry beams aligned with the gallery walls. The exterior wall is concrete faced with Portland stone, Cornish granite, or Ibstock brick; the roof with its clerestory lanterns, on the other hand, is carried on a steel frame. This steel structure is hidden, and with few exceptions concrete columns are concealed inside walls. While some of the visible columns in the Sainsbury Wing carry loads, there are several that are what Venturi called “symbolically structural”—that is, fake. A row of columns in the entrance foyer, for example, and the Tuscan columns in the archways of the galleries, are in the latter category; so is a series of arched trusses above the main staircase. Deliberately using structural elements in nonstructural ways has a long history. The most obvious ancient example is the pilaster, which looks like a flattened column but carries no load. “The pilaster is a lie,” observed Goethe disapprovingly.

Venturi is the leading modern mannerist. The colonnade of the entry porch of the Vagelos Laboratories at the University of Pennsylvania consists of irregularly spaced single and double columns. Some carry loads, some don’t; some line up with the structural grid of the reinforced concrete frame that supports the five-story building, some don’t; some line up with the brick piers of the façade—only some of which are structural—some don’t. What is the reason for this intricacy? In part, it reflects the complex program of the building, which houses offices and laboratories for bioengineering, chemistry, chemical engineering, and medicine. In part, Venturi is grappling with an architectural problem of the site: how to create a main entrance façade on the short end of a building. His solution is to make the façade complicated, contradictory, and paradoxical. He hints that the columns should not be taken altogether seriously by giving them stylized, flattened, almost cartoonish capitals, and by separating the capital from the wall above. The games that Venturi plays with structure are also an hommage to his Victorian predecessor Frank Furness, whose highly mannered university library stands across the street.

Venturi, Scott Brown & Associates, Roy and Diana Vagelos Laboratories, University of Pennsylvania, Philadelphia, 1997

The Los Angeles architect Thom Mayne favors materials that are industrial-looking but he is likewise a mannerist. The U.S. Federal Building in San Francisco is a narrow eighteen-story office slab with a façade shrouded in a perforated-stainless-steel skin that is mysteriously sliced and peeled away, apparently at random. At the entrance, a column leans perilously aslant. The leaning column is real, but what about the beam that forces its way out of the wall and stops short of the column? Like a dropped keystone in a Renaissance building, it suggests instability—hardly what we expect in a government building. The Federal Building abounds in such contradictions. Alongside a walkway is a giant garden pergola with a steel structure as heavy—and as un-garden-like—as the underside of stadium bleachers. The most striking feature of the entry façade is a mundane fire escape, casually draped over the building. Comparing harmony and dissonance in architecture, Venturi wrote that wearing a gray tie with a gray suit was an example of harmony, wearing a red tie with a gray suit was “contrasting harmony,” while wearing a gray tie with red polka dots was “dissonant harmony.” Mayne’s unruly building goes a step further, dispensing with the tie altogether, and leaving the shirttail hanging out, in what might be called “dissonant disharmony.”

Thom Mayne/Morphosis, U.S. Federal Building, San Francisco, 2007

Some architects play with structure, others simply ignore it. In the chapel at Ronchamp, Le Corbusier created a pillow-like roof that looks like solid concrete but is really a diaphragm made up of two thin skins separated—and supported—by hidden internal girders. The roof rests on roughly plastered walls that appear massive but are actually hollow—cement sprayed onto a metal mesh—and conceal a concrete frame. At Ronchamp, Le Corbusier hides what holds the building up and even creates make-believe structure.

Gehry Partners, Jay Pritzker Pavilion, Millennium Park, Chicago, 2004

Ronchamp was built in the 1950s. Today, buildings that resemble large sculptures are commonplace. There are columns here and there at the de Young Museum, but the steel structure is concealed, even in the fifty-five-foot roof cantilever that mysteriously hovers over the café terrace. The cantilever, like the outlines of the building, is dictated by formal considerations. The structure of Disney Hall is a steel frame, and is likewise inconsequential to the animated exterior, which is purely sculptural. Gehry’s casual attitude to construction is even more evident in the outdoor band shell that he designed for Millennium Park in Chicago. A band shell is required to be a sound reflector, and Gehry creates a wooden backdrop for the stage, framed by wavy, stainless-steel, sail-like forms. These forms are supported by a utilitarian framework of steel props and braces that cannot be seen from the grassy seating area, but is completely visible from the sides and rear and is as prosaic as the back of a billboard. This seemingly makeshift solution is light-years away from the ordered solidity of the Parthenon. Perhaps it reflects Gehry’s view of our improvised and unruly modern condition.