DEVELOPMENTS IN THE CONSTRUCTION OF TALL BUILDINGS
Until the nineteenth century, most tall buildings were constructed of load-bearing masonry walls. Masonry walls had to be thick, particularly at the base, to support a building’s great weight. Stoneworkers built these walls by placing stone upon stone or brick upon brick, adding strength and stability by placing layers of mortar or cement between the stones. Floors and roofs had to be supported by wooden beams, but the major vertical force of buildings was supported by thick masonry walls. This imposed serious limitations on the number and size of windows.
In the 1850s, an alternative was emerging that would eliminate the need for exterior weight-bearing walls: a three-dimensional grid of metal beams and columns. The introduction of metal construction made it possible to build larger interior spaces with fewer columns than before. The new construction was capable of supporting all the loads to which a building might be subjected, including the vertical forces caused by the weight of the floors and the horizontal forces caused by the wind or earthquakes.
The first buildings to depart from the load-bearing wall tradition were iron-framed. Wrought iron, shaped by hammering the heated metal or rolling it under extreme pressure, contains almost no carbon, and when used as floor beams, it can support a great deal of weight. An interior wrought iron skeleton supported all of the building’s weight. Exterior walls of reinforced concrete acted mainly as weatherproofing. As masonry yielded to concrete, walls that once bore weight evolved into thin curtain walls that would allow more windows. These modifications produced sturdier, lighter, and taller buildings that quickly became known as skyscrapers. Skyscrapers satisfied the growing need for office space, warehouses, and department stores. Buildings of eight or more stories quickly transformed the city skyline and dominated the central business districts of American cities such as New York, Chicago, and St. Louis.
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