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FYIStructure: Defying gravity

  1. Bridges
  2. How buildings stand up<
  3. Earlier structural methods
Bridges and Buildings
FYI Structure<

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How buildings stand up

The same steel frame that allows bridges to span long distances without succumbing to compression and bending also allows skyscrapers to resist the compression of their many tons soaring into the sky. Steel is one of the few building materials that are equally capable of withstanding the stresses of compression, tension, and bending. Unlike bridges, larger buildings hide their steel "skeletons" with a layer of "skin" or cladding, a façade of glass, aluminum, stone, brick, or more steel. This layer functions much like human skin, too: It keeps rain, wind, and temperature extremes outside.

Pittsburgh History and Landmarks Foundation

In this photo of Gateway Center under construction, stainless steel cladding is being attached to the building's steel frame skeleton.


Downtown sports an eclectic assortment of skyscraper styles, and with an alert eye, a simple walking tour of the Golden Triangle could turn into a revealing history of skyscapers.

Fourth Avenue, one of the most well-preserved historic districts downtown, is a great place to begin exploring the brief, but soaring, history of the skyscraper. The street was known decades ago as "Pittsburgh's Wall Street," since it was the site of many of the city's banking institutions that fueled the industrial revolution. (In 1913 more money exchanged hands every day in Pittsburgh than in any other city but New York!)

Clyde Hare for Pittsburgh History and Landmarks

Three early skyscrapers of Fourth Avenue-- the Benedum-Trees, Bank Center, and Arrott Buildings--stand behind the older buildings along Fort Pitt Boulevard and in front of the newer skyscrapers of the Renaissance.

Fourth Avenue is home to a long parade of what was, at the turn of the century, a brand new building form. As the invention of elevators and steel frame construction made tall, skinny buildings possible, architects of the day turned to the classic tall, skinny column for inspiration. Look for a column's base, shaft, and capital (fancy top) in the shape of the Bank Center, the Arrott Building, the Times (Magee) Building, the Benedum-Trees Building, or the nearby Park Building, the oldest skycraper still standing.

The Carnegie Building, Pittsburgh's first skyscraper (now gone), is an example of the column formula commonly used in designing the first skyscapers. Rollover the photo to view base, shaft, and capital.

Pittsburgh History and Landmarks Foundation

In spite of their thoroughly modern steel frames, these buildings are embellished inside and out by intricate carvings and distinctive architectural styles of the past. Original marble and brass fixtures exist to this day in many of the buildings, and one can even find such artifacts as the Arrott Building's original elevator (the very invention that made such skyscrapers possible!), and a bank vault with a five-ton door in the Frick Building. Even young children unaware of formal architectural terms can appreciate the many carved lions, dragons, gryphons, and gargoyles lurking on these buildings' exteriors!

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Another historic avenue is Grant Street, once known as Grant's Hill but bulldozed over the years so that it is now two stories lower than it was originally. Grant Street is a great place to scout for the next generation of Art Deco skyscrapers: the Koppers Building, the Gulf Building, and the Grant Building.

The Koppers and Gulf Buildings, are prime examples of the "Golden Age of Skyscrapers." The tapered forms of 1920s' and 1930s' skyscrapers of the were often topped off in a grand way--the Gulf Building has a weather beacon!

Pittsburgh History and Landmarks Foundation

These skyscrapers are typical of the Golden Age of Skyscrapers that gave birth to the Chrysler and Empire State Buildings in New York City. Instead of going straight up, notice how they get narrower as they get taller to let light into the streets below. These Golden Age ‘scrapers are often topped off with amazing flamboyant features. At night, a blinking red light flashes at the top of the Grant Building. Look closely and you'll notice a pattern in the flashing light. Believe it or not, that light is spelling out P-I-T-T-S-B-U-R-G-H in Morse code! When it was built in 1929, pilots used the flashing light as a navigation beacon.

Another flashing light on top of the Gulf Building offers a whimsical attempt at meteorology. Over the years, the top of the Gulf Tower has flashed a sequence of red and orange lights to indicate weather patterns! Built in 1932, it was for years Pittsburgh's tallest building. Today it is home to many businesses – although the most unique tenants actually live on the roof! A family of peregrine falcons has defied nature by building its nest on top of the Gulf Building. Peregrine falcons prefer to live on the edges of cliffs, but in this case, these magnificent birds-of-prey find the Gulf Building to be an adequate substitute nesting area and the resident pigeons plentiful prey.

The fanciful interior of the Cathedral of Learning, is called "The Commons" and is styled after medieval cathedrals, but behind its stone cladding is a frame of steel.

Below: Cathedral of Learning under construction, showing its steel frame.

Cathedral of Learning CommonsCathedral of Learning Commons
Tom Altany

University of Pittsburgh


Another example of this kind of imagnization applied to skyscrapers occurred in the 1930s with University of Pittsburgh Chancellor Bowman's vision of the world's tallest classroom building. The Cathedral of Learning was built with gothic cathedrals in mind and housed the Nationality Classrooms as a tribute to the many ethnic groups that built Pittsburgh.

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Gateway Center, the Alcoa Building (1951), and the USX Tower (1971) are monuments to the International Style of architecture that inspired the post-World War II skyscrapers of Pittsburgh's first Renaissance. The International Style uses basic shapes without ornamentation, letting the methods and materials of construction speak for themselves. These buildings, which commonly take up their whole block, are fitting advertisements for Pittsburgh's manufactured wares: steel, aluminum, and glass.

Pittsburgh History and Landmarks Foundation


The Alcoa Building (left) is a perfect example of the International Style of the post-World War II era. Structural elements--in this case aluminum modules with glass port-hole windows--become the exterior decoration. USX Tower wears its steel frame on the outside!

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PPG Place -- just one of the remarkable skyscrapers that joined Pittsburgh's architectural landscape during a phase of construction in the 1980's known as Renaissance II -- along with Fifth Avenue Place and CNG Tower are Post-Modern designs that have tried to go back and recreate some of the time-tested architectural elements of the past, using modern materials.

PPG Place (1984), a Renaissance II skyscraper, combines modern reflective glass with traditional Gothic pointed arches and soaring towers.

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