World Trade Towers design exceeded wind load codes

World Trade Towers design exceeded wind load codes

Single frame of a computer simulation (containing 90,000 elements) of the WTC North Tower as it responds to wind loads.

Full size image available through contact

The National Institute of Standards and Technology (NIST) reported on Sept. 17 that it has done additional analysis of the wind "loads" that the World Trade Center (WTC) towers were originally designed to resist--critical data to help the agency better assess the overall strengths and baseline performance of the two buildings before they were brought down by the terrorist attacks of Sept. 11, 2001. The work is being conducted as part of NIST's federal building and fire safety investigation of the WTC disaster.

NIST recently completed its review of the original 1960s-era source documents containing wind tunnel test data and wind load estimation methods used for the towers, calculated the wind load estimates based on a clearer interpretation of this information, and determined the values actually used in the design of the buildings. These clarified original design wind load estimates all exceed those established by the New York City building code prior to 1968 (when the WTC towers were designed) and through 2001 (when the towers were destroyed). The values also are higher than those required by other selected building codes of the era, including the relevant national model building code.

Wind load capacity is a key factor in determining the overall strength of a tall building and is important in determining not only its ability to withstand winds but also its reserve capacity to withstand unanticipated events such as a major fire or impact damage.

The NIST investigation team's final report is scheduled for release as a draft document in December 2004. For more information on the new findings, go to


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