A Better Building, A Brighter Tomorrow

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Kate Critchfield

Professor Carl E. Clark

Interior Codes and Regulations ID326W

Scottsdale, AZ

September 13, 2007

A Better Building A Brighter Tomorrow

The catastrophic event of 9/11 sparked an interest in fire safety and building codes. The large number of deaths that occurred from this incident led many Americans to ask, “Why?” Other people thought, “What could we have done differently?” As with any tragic scenario, people live and learn to achieve better concepts to bring a brighter tomorrow. Better building concepts for future and existing high-rise buildings will require more stringent fire codes, non-combustible materials at interior cores, and implementation of a universal communication system amongst first responders to ensure the safety of building occupants.

The Twin Towers were built to be taller, more economical and more modern than any other buildings in existence (Nova). They were constructed with 200,000 tons of steel, 425,000 cubic yards of concrete, 103 elevators, 43,600 windows, 60,000 tons of cooling equipment, and a 360 foot television antenna. The North Tower was finished in 1970, reaching a height of 1,368 feet tall. The South Tower was completed in 1973 and stood 1,362 feet high (Avery).

Since the 19th century, conventional skyscrapers were typically built with a skeleton of interior support columns equally spaced throughout the structure, minimizing the area of leased office space. The exterior walls did not carry any load-bearing weight. However, the construction of the North and South Towers repositioned support columns to maximize rental space. The exterior walls of the Twin Towers were structurally designed as the load-bearing walls, which supports the weight of the floors. The only other structural columns found in the interior of the Towers were located at the interior core. The exterior walls not only support the weight of the floors, the outer walls also withstand strong winds and carry the vertical loads. “The wall consists of closely spaced vertical columns (21 columns 10 feet apart) tied together by horizontal spandrel beams that girdle the tower at every floor. On the inside of the structure the floor sections consist of trusses spanning from the core to the outer wall” (Dunn). The exterior of the buildings could even withstand the impact of a Boeing 707, the largest plane in existence at the time of construction (Nova).

In 1968 the performance building codes of New York City superceded the Building Code enacted in 1938. The new building codes were based on “nationally accepted performance standards and specifications for materials and construction assemblies” (“About the Building Code on the Web”). The new codes allowed a spray-on fire retardant to be used in lieu of the concrete encasement fire protection. The architects of the World Trade Center took full advantage of the implementation.  A trend in modern high-rise construction was to use more steel and shape lightweight steel into different shapes to increase its load bearing capability. “The WTC has tubular steel bearing walls, fluted corrugated steel flooring and bent bar steel truss floor supports. To a modern high-rise building designer steel framing is economical and concrete is a costly material. For a high-rise structural frame: columns, girders, floors and walls, steel provides greater strength per pound than concrete” (Dunn).  It is common knowledge among architects, and building designers that concrete is a heavy material and adds excess weight to a structure.  The use of alternative materials to concrete inside of a structure will make the building weigh less.  Columns, girders and beams that are smaller in dimension can be used to build a lighter building, decreasing the cost of materials. This concept also allows a taller structure to be built from the same size steel framing (Dunn).

Approximately 50,000 occupants worked at the World Trade Center and thousands of daily visitors passed through the buildings doors. The North and the South Towers had three central stairwells that ran straight up and down the interior core, with the exception of where the transfer hallways were located. The hallways had smoke doors that prevented smoke from traveling to other parts of the buildings. The doors leading to the roof was kept locked since no rooftop evacuation plan existed and also due to the fact that the roof was cluttered and impractical for helicopters to land on. Therefore, helicopter evacuations were not incorporated into the World Trade Center fire safety plan (Natl. Comm’n on Terrorist Attacks Upon the U.S. 288).

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After a bomb exploded under the World Trade Center in 1993, power was lost and communications halted, even the generators were shut down for safety reasons. This affected the Fire Departments rescue efforts to maneuver through unlit, smoke filled stairwells and the firefighters inability to use their radios in such large buildings. Millions of dollars were spent to address the shortcomings displayed after the bombing. Working under the guidelines of the 1968 performance building codes of New York City, enhancements to the power sources, exits signs, and the fire alarm systems were made.  Plans to improve the fire emergency preparedness ...

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