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I N S I G H T : M AasS Oo Nn Rr Yy & Cc Oo Nnc C Rr Ee Tt Ee Buildings Count on Concrete NG Ng SAI sai KIT kit Continued improvement in concrete strength helps the development of high-rise buildings in the U.S. and throughout the world hile concrete is more common ly used W HILE to construct low-rise buildings, continued improvement in concrete strength over the last decade has been a major factor in the development of taller buildings in the United States and throughout the world. New structural systems – including high-strength concrete – created either from concrete alone or with a composite system that includes both concrete and structural steel are partly responsible. These systems enable skyscrapers to resist the enormous wind and earthquake loads imposed along their height and allow these structures to support the vertical loads created by gravity, the weight of the building, and its occupants. A major advantage of concrete construction for high-rise buildings is the material’s inherent properties of heaviness and mass, which 70 Tt eE x X a A s S a A r R c C h H iI tT eE c C tT create lateral stiffness, stiff ness, or resistance to horizontal movement. Occupants of concrete towers are less able to perceive building motion than occupants of comparable tall buildings with non-concrete structural systems. As a result, concrete has become the material of choice for many tall, slim towers, including many squeezed into narrow building lots in New York City in recent years. Engineers deemed concrete to be the only viable structural option for the structures – including City Spire on West 56th Street, with its slenderness ratio of 10 to 1 – to withstand anticipated wind loading. The fi first rst reinforced concrete high-rise was the 16-story Ingalls Building, completed in Cincinnati in 1903. Even 50 years later, concrete buildings rarely exceeded 20 stories. Concrete high-rise buildings were not economical to At 1,378 feet tall, the twin Petronas Towers in Kuala Lumpur, Malaysia, designed by Cesar Pelli, dramatically demonstrates the strength of composite structural systems. lease because the massive columns needed for their support left too little rentable floor floor space. Greater building height became possible as concrete strength increased. In the 1950s, 5,000 psi (34 MPa) was considered high strength; by 1990, two high-rise buildings were constructed in Seattle using concrete with strengths of up to 19,000 psi (131 MPa). Ultra-high-strength concrete is now manufactured with strengths in excess of 21,750 psi (150 MPa). 1 / 2 2 0 0 6

Texas Architect Jan/Feb 2006: Schools

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