建筑细部︱埃克塞特图书馆 Exeter Library


After the Richards laboratory Kahn executed a number of brick buildings, beginning with the Unitarian Church at rochester. This was in part inspired by Saarinen’s chapel at MIT, although Kahn’s response to the chapel was largely negative. Saarinen’s chapel used load-bearing brick masonry and brick arches at a time when both were taboo in the Modern movement providing a precedent for what Kahn was to do next, not just the revival of archaic masonry techniques but a rethinking of the relationship between structure and space in Modernism.


This relationship in typical postwar American buildings was a highly bastardized version of Le Corbusier’s free plan. While the steel and concrete frame had made possible the independence of structure and plan, the major aesthetic consequence of this-the ability of spaces to interconnect and interlock, to”flow”together- was rarely used for obvious functional reasons. The net result was not “a new world of space, but simply that structural and spatial divisions of the building became independent. Spatial layouts, while retaining traditional cellular character, lost the order imposed by load-bearing structure, while the structure itself was likely to go completely unnoticed. Kahn was not alone in finding this unacceptable, but he went further than others in insisting that the structural divisions of a building and its spatial divisions must coincide, however small those divisions might be A person standing in a space must perceive the structure of that space.


Coupled with Kahn’s revival of interest in traditional spatial and structural systems was an increased use of traditional masonry assemblies. To him there were definite rules about the way brick could be used. Steel lintels or other types of concealed reinforcement were rarely acceptable, and in his later work openings were invariably made with arches, usually segmented. In some early masonry experiments, such as the Tribune Review Building in 1958, he differentiated between bearing and nonbearing walls by the use of different types of concrete block, but after 1965 masonry is seldom used as a curtain wall The basic structures used at the rochester church——modern, open, concrete-framed space on the interior and traditional cellular, masonry space on the exterior——provided the best of both worlds and were to form the basis for numerous subsequent Kahn works.


Kahn said of his library for Phillips Exeter Academy: “I felt that a reading room would be a place where a person is alone near a window… a kind of discovered place in the folds of construction.”


The order of space at Exeter, as at Rochester, is concentric rings of different structures of different materials-in Kahns terms, doughnuts. The innermost has no assigned use: a concrete cube with a large circular opening on each side is supported by four concrete piers at 45 degrees to the primary grid. An X brace of one-story-deep concrete beams spans the top and supports the skylight above. In theory this structure is a folded plate acting to laterally brace the entire building. At a glance it seems somewhat structurally excessive for an eight-story building, and perhaps owes more to a desire for structural expression than to structural necessity The second doughnut holds the books.


Concrete flat plates are supported by concrete columns in square bays on the four sides. On the ground floor this area is used for the circulation desk, card catalogue and a grand stair, and the three square bays of each side are merged into one by means of eliminating the two center rows of columns. This requires a transfer structure at the second floor to pick up the load of the lost columns. Here the concept of one structure for one space is carried to extreme if not excessive limits.Is a 40-foot free-span space really necessary for a space housing a card catalogue?The outer layer is composed of brick bearing walls supporting a flat-plate concrete slab. Lateral bracing is provided by brick crosswalls dividing the doughnut into a series of rooms, each containing two windows and four built-in carrels.


Like Frank Lloyd Wright, Kahn desired monolithic exterior walls, unfinished so that the interior and exterior surfaces were the same, but like Wright he faced the difficulty of the ayered nature of the modern wall. Although solid brick walls are often used in contemporary construction, the typical contemporary masonry wall contains within its thickness a cavity for waterproofing, insulation to retard the flow of heat, a vapor barrier to prevent condensation, and metal reinforcing to tie the whole thing back together again. In addition to hindering Kahn’s simple desire for monolithic building, this complicated assembly did not fit easily into his philosophy. A wall was not to him a machine. Each material and component–brick, concrete, ductwork -had its own”order. ” An assembly of specialized components such as the modern brick wall, was not easily reconciled with this way of thinking.

在条件允许的情况下,卡恩建造了单片墙,比如在印度和巴基斯坦,那里的建筑和建筑性能标准没有那么专业。印度管理学院(Indian Institute of Management)有8至24英寸厚的整块砖墙,采用粘结模式铺设。(有趣的是,勒柯布西耶(Le Corbusier) 10年前在这座城市建造的Millowner大楼使用了空腔墙。几乎所有卡恩设计的美国建筑都使用空洞和刚性隔热材料。他很少不止一次地用同样的方法来解决他的问题,而这些墙的发展表明,他一直在努力使他的建筑哲学与当代美国实践的现实相协调。

When conditions permitted, Kahn built monolithic walls, such as in India and Pakistan, where construction and standards of building performance were less specialized. The Indian Institute of Management has monolithic brick walls 8 to 24 inches thick laid in bonded patterns. (Interestingly enough, the Millowner’s building built by Le Corbusier in the same city ten years earlier had used a cavity wall. Almost all Kahn’s American buildings use cavities and rigid insulation. He rarely used the same solution to his problem more than once, and the development of these walls shows an ongoing effort to reconcile his philosophy of construction with the realities of contemporary American practice.


Before Exeter Kahn had used two types of brick exterior wall. The first, used in India and Pakistan, was a true monolithic wall, and had the richness of detail and bonding patterns of traditional brick walls. The walls of Richards and Rochester were modern, specialized, and sophisticated, but lacked the visual qualities of the first wall type, particularly the absence of bonding patterns. At Exeter Kahn sought to combine the two.


The Exeter wall has two layers, an outer layer of 12-inch-thick brick and block which is a bearing wall and an inner layer of 4-inch-thick brick which is a curtain wall. The cavity between holds insulation vapor barrier, and waterproofing as in a traditional cavity wall. The outer wall is bonded in a pattern resembling common bond, while the inner, being only one brick thick, is in simple running bond. This is an inversion of the wall type used at Rochester, or for that matter the typical masonry cavity wall, where the thinner layer is placed on the outside. The advantage of the Exeter wall is purely visual since it exposes the bonded structural portion of the wall to the exterior. This may seem to many a result so subtle as to be hardly worth the effort, but to Kahn’s eye the Exeter wall was everything that the Rochester wall was not.

埃克塞特是卡恩最纯粹的砖结构。这里很少用砖作幕墙材料。至少在概念上,每一块砖都有助于建筑的结构支撑。没有钢或其他隐藏的门楣。承重墙上的每一个开口都是一个带有平拱的框架(具有非常浅的曲线的拱)。在传统的砌体结构中,随着荷载的增加,墙体往往向底部加厚。埃克塞特墙的厚度是恒定的,但每个桥墩的表面尺寸比上面的地板宽一块砖。因此,这些桥墩有一个明显的锥形,使它们看起来有点像埃及的塔。有许多码头之间的开口是不透明的地方,但这里的空间充满了木镶板,砖,表明非结构化。根据Jay Wickersham的说法,整个外墙是无承重的,因为楼板的加固模式将荷载带到隔间之间的交叉墙。然而,和所有的结构理性主义者一样,卡恩在表达一些东西的同时也隐藏了另一些东西。例如,楼板以一种相当复杂的方式与墙壁相接。在桥墩处,它向下弯曲几英尺,以便在这些桥墩之间的拱处提供额外的支撑,桥墩被往后拉,这样楼板就不会压在桥墩上。外观上没有显示这个复杂组件的任何提示。

Exeter is the purest of Kahn’s brick structures. Rarely is brick used here as a curtain wall material. At least conceptually, every brick contributes to the structural support of the building. There are no steel or other concealed lintels. Each opening in the bearing wall is a frame with a flat arch (an arch with a very shallow curve). In traditional masonry structures a wall often becomes thicker toward the base as the load increases. The Exeter wall is of constant thickness, but each pier is one brick wider in its face dimension than that of the floor above. As a result there is a noticeable taper to these piers that makes them appear something like Egyptian pylons. There are many places where the openings between piers are opaque,but here the voids are filled with wood paneling, not brick, to indicate that they are nonstructural. According to Jay Wickersham the entire exterior wall is nonbearing since the pattern of reinforcing in the slab carries the load to the cross walls between cubicles. Like all structural rationalists however, Kahn expresses some things while concealing others. The floor slab, for example, meets the wall in a fairly complex way. At the piers it turns down several feet for additional support at the arches between these piers it is held back so that the slab does not bear on the arch. No hint of this complicated assembly appears on the facade.


The details that show Kahn at his best are those that describe what the building is not. Due to the need for lateral bracing one would expect this building to have heavy solid corners. It does not; the corner is broken open to show the edges of each wall, thus demonstrating that there is an internal concrete frame bracing the building and making the solid corner unnecessary. A similar condition occurs at the inner wythe of the exterior wall. This layer of the wall is nonbearing fact it is separated from the wall by a compressible filler to ensure that the concrete slab does not bear on the wall-and it is in this wall that the only lintels in the building, the red sandstone ones over each opening, occur. This opening could have been spanned with an arch as is the outer layer, and perhaps it would have looked better if it had been, but Kahn does not want to mislead us as to the nature and function of this wall ie,he does not want the arch to appear to support the slab.The wall could have been made to appear to be monolithic, and most observers probably assume that it is, but Kahn refuses to deliberately deceive us. 


The system of exposed and integrated utilities used at the Richards Building and Rochester was not abandoned but heavily modified, primarily because Exeter is an eight-story building. Like other buildings of comparable size, it has two mechanical systems, one for the perimeter and one for the interior spaces, due to the differing conditions of their heating and cooling loads. The perimeter system, rather than aur, uses water, which requires only small pipes for distribution and thus does not pose the same problems of spatial accommodatio as an air system with ductwork.


Each corner of the building contains a core for fire stairs, toilet rooms, etc.,that also contains vertical shafts to distribute air to each floor. The air is distributed on each level by two round horizontal ducts running above the corridor that separates the book areas and the reading areas The diffusers that distribute the air are for the most part located in the ducts themselves but occasionally a duct will turn, penetrate the wall, and reemerge as a linear diffuser. These diffusers, unlike the simple slots used at Rochester, can be modified to control the flow of air. It should be noted that, appearances to the contrary, the ductwork is rarely exposed.


The fenestration system at Exeter is a variation of that developed for Salk, although the method of forming structural openings is in some ways the opposite. The typical opening in the exterior wall is two stories high, with a carrel at its base containing a small view window and a large single light above to light the reading room interior. The glass of the larger high window is set as deep into the wall as possible, and the wood frame is recessed into the brickwork. Kahn sought to make the glass almost invisible, to achieve the quality of a ruin. By contrast the lower window is placed flush with the face of the exterior wall, and the small view window is set only as deep as the glazing detail requires. This window is not operable but an interior wood panel may be slid across the opening, omitting the view but preserving the light above. As at Salk all exterior wood is teak; all interior wood is clear-finished white oak.