The curtain wall dichotomy can be traced back to numerous 19th and early 20th Century antecedents. In the United States curtain wall development became intertwined with that of the skeleton frame. Skyscrapers would not have been technically feasible without the lightweight curtain wall. And it was through the skyscraper that the curtain wall achieved its greatest realization.
In the nineteenth century, engineers first utilized metal frame construction in bridges, factories, and warehouses, and cast and wrought iron were the major metals used in construction. The invention of the Bessemer process in England in 1856 made it possible to produce large quantities of steel affordably. In the United States, steel production on a large scale was realized in the 1870s. The transition from iron to steel was gradual, with iron still used in building construction as late as the 1890s.
Arguably, the first metal skeleton-framed skyscraper was the Home Insurance Building designed by Jenney in Chicago. In this structure, column loads were transferred to stone pier footings via the metal frame without load-bearing masonry walls. Each level of the exterior wall was supported on a shelf angle fixed to the spandrel girder. At that time skyscrapers were designed without lateral bracing under the assumption
that the heavy masonry cladding provided sufficient rigidity for the whole structure.
As skeleton framing came into common use, masonry bearing wall construction reached its practical limit. Burnham and Root's 16-story Monadnock Block (Chicago, 1891) utilized traditional load-bearing masonry walls which at grade were almost 2 meters thick. This building also utilized the first rigid frame for lateral stiffness. At the same time, Burn-ham and Root developed a complete steel frame for the Rand McNally Building (Chicago, 1890). They also developed a steel frame laterally stiffened with a diagonal bracing system in the 20-story Masonic Temple (Figure 2). Within a three year period the same firm had erected a bearing wall; steel frame; and a diagonal-braced metal frame skyscraper revealing the experimental and quickly evolving nature of the typology.
Several years later, the structural innovations of the Chicago school were taken further by D.H. Burnham in the Reliance Building (Chicago, 1895). The exterior bays were designed as rigid steel frames, and two-story columns erected with staggered joints further increased frame rigidity. The construction of the Reliance Building also illustrated all of the
familiar construction techniques which had come into widespread use at the end of the 19th century to facilitate rapid construction. The construction site was lit so work could continue into the night. Work spaces were enclosed and heated so the project could proceed during the winter months. The structural frame, which began erection in mid July of 1894, was topped off on August 1 and required only 15 days.
Steel and then concrete skeleton framing soon became universally accepted for skyscrapers. Thereafter, improvements of known design methods encouraged the construction of increasingly taller buildings.
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