Ten Years Later — What Have We Learned?
Progressive Collapse: After the failure of the column systems, the buildings’ floors appeared to fall nearly straight down in a floor-by- floor collapse.
Perhaps the greatest changes resulting from 9/11 were to building codes. Prior to the attack, the focus of occupant safety related to building codes primarily focused upon getting people out of a burning high-rise, a’la “Towering Inferno”. The critical issue following 9/11 for structural engineers became what is known as “progressive collapse”. Progressive collapse occurs when the failure of one structural element results in the failure of adjoining or adjacent structural elements, causing complete structural collapse. To address such phenomenon, authorities have instituted additional fire proofing requirements for structural elements, including the fireproofing that will withstand a one thousand pound, per square inch impact.
Photo by: Jordi Sanchez
In addition to progressive collapse design considerations, architects and engineers must also consider the safe and rapid evacuation of tenants from upper floors. New building code requirements regarding occupant evacuation include installation of third exit stairways inside buildings taller than 420 feet, and luminous markings in stairwells and passageways showing the exit path in buildings more than 75 feet tall, to assist tenants during a power failure.
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Posted by FanningCommunications
on Sep 1st, 2011 and filed under Feature Story
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