The Cartesian skyscraper was thus redesigned to respond to its own mechanical naturalism–its structural parti was now a tripod, or “crow’s foot”–allowing the building to be exposed to the sun on all sides.
”This ritual procession began to crystallize with the appearance of large openings corresponding to the overall scale of the building, which focused and dominated its composition.
”Superimposing geometric proportions, which were only ever an approximation, on the exposed grid of the curtain wall was not easily reconcilable with mathematical repitition.
”The technical floor, the suspended ceiling, and the structural system were thus incoporated within an integrated entity that determined the flexibility of the overall space. The section of this building volume, its spatial rationality and economy, the degree of freedom it offered in the design of energy systems, and its exterior appearence or presence became themes explicitly examined in contemporary architectural practice.
”In a building of standard proportions, high-rise principles of construction began to apply at around twenty stories. At this height, the lateral forces on the building, traditionally absorbed by the massiveness and equilibrium of masonry walls, emerge as principal factors affecting the structural system.
”The structural system can be divided up into elements determined statically and resolved through simple statics.
”The first large-scale vertical structures reproduced the strengthening function of the traditional wall by introducing rigid portal frames in the exterior bays to resist wind load. Soon, however, the need for unobstructed usable space caused this strengthening function to be repositioned to the interior circulation core, superimposing a rigid shear wall onto a conventional isostatic frame. These transitional solutions extended the stable structural system to around forty stories.
”“We have arrived at an apparently paradoxical conclusion,” he stated; “the art of a structure depends on knowing how and where to locate the voids.” Structural materials resisting similar forces must adopt similar systems of spatial organization for maximum efficiency.
”If wind is the principle stress acting on the high-rise building, then the structural response is characterized by flexicon: the building deflects. Nature, however, offers models for counteracting this problem: inflexible, hollow spatial organizations that transform wind loads into simple compression and tension through tetrahedral geometry.
”there was an implicit contradiction between the vertical circulation systems and the structure’s movement.
”the distinction between the structural coherence of spatial triangulation and the conventional rectangular geometry of usable space produced a specific typological dialectic that circumscribes the later development of the high-rise.
”acknowledged flexicon in the tie bars and joints and retained the correspondence between spatial structure and function.
”On Growth and Form…This text applies Galileo’s mechanical analyses to the relationships between form and growth in nature, concluding that unlimited growth in forms that come “from art or nature” was impossible without changes in the load-bearing capacity or proportion of the structure.
”every increase in size is accompanied by a decrease in efficiency. This is not always true, and there are many structures whose increasing efficiency due to increasing volume with proportionately decreasing surface continues up to the limits of the strength of the materials.
”since every increase in size is accompanied by a disproportionately higher increase in volume than in area, these structures become more stable as they increase in size.
”This transformation was characterized by the decomposition of the structural system in response to specific forces and functional demands, components placed on the periphery of the building in response to wind load, appropriate adjustments to scale, and increasing specialization of load-bearing and structural materials.
”In a simplified description one could say that, subject to variable wind pressure, a skyscraper sustains a vibration that causes it to oscillate, or sway, continuously around an intermediate position, the deflection from which is determined by the mean wind pressure.
”all of the elements of the building’s skin might function together as a complete three-dimensional tensile model.
”Replacing the grid with this diagonal superstructure also led to more rational skyscraper construction. Vertical loads are redistributed by the diagonals among the columns in such a way that, in spite of their specific tributary areas, all the columns on the same floor have equal dimensions.
”In a hypothetical, square-plan building, the ideal layout would concentrate this mass at the corners, thereby achieving maximum inertia.
”Using concrete for bending moment and steel for shear was an abstract and ideal solution that opened the way to a hybrid concept of structural systems.
”Aeroelastic tests suggested different ways to optimize a building’s performance under wind load. Altering the building’s general form to improve aerodynamic penetration, altering the section to affect the vibration period, altering the surface texture of the building envelope to absorb lateral forces, and using exterior systems for diverting or breaking up the wind
”One can use irregular shapes or highly textured surfaces on the building skin to create areas of turbulence, producing a cushion of air surrounding the building that transforms the wind’s kinetic energy into thermal energy though the effect of friction.
”Contemporary high-rise construction bears in particular the imprint of several key transformations that took place following World War II. Among these were the advent of the ideal of continuous, unobstructed open space; the three-dimensional configuration of the structure; the recognition of the pure, repetitive prism as no longer being the most structurally valid form; and the concept of the building envelope as an active element in the structure’s mechanical performance.
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