After the Blastby Paul Tarricone, Assoc. Editor;
Serial Information: Civil Engineering—ASCE, 1993, Vol. 63, Issue 5, Pg. 44-47
Document Type: Feature article
Abstract: On February 26, 1993, a bomb exploded in an underground parking garage beneath the World Trade Center, killing six, causing hundreds of millions of dollars in damage and leaving a crater roughly 100 ft wide by 200 ft deep. Less than a month later, the twin towers reopened, thanks in part to an emergency rehab scheme that allowed the blast area to serve as both construction site and crime scene in a matter of days. After the explosion, the immediate structural threat was to seven columns each measuring more than 50 ft long. The seven columns had been laterally braced by the concrete parking slabs. When the blast tore out the slabs, the columns were left laterally unbraced for distances up to 60 ft in some areas. The solution was to shore up the columns with 6 in. square, 35 ft long steel tubes, which were slid through holes drilled in the floor above and welded horizontally or diagonally to the columns by workers lowered down the holes in a spider cage. Eighteen steel tubes were needed to brace the seven most precarious columns, which took about five days. Eventually 16 columns were restored to full strength in this manner. After completion of the emergency work, debris removal has proceeded virtually around the clock. The next key milestone is bringing seven massive mechanical chillers, located three levels down from the blast, back on line to air-condition the buildings beginning May 1. Despite the impressive comeback of the World Trade Center, questions remain about the thousands of other vertical cities dotting the nation's urban landscape and whether it's realistic, cost-efficient or even possible to make them invulnerable to terrorist attack. A number of experts discuss what can be done to protect high-rises in the future.
Subject Headings: Bracing | Columns | Explosions | High-rise buildings | Multi-story buildings | Parking facilities | Rehabilitation | Structural reliability |
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