'Heat from fire dealt the punishing blow'

NEW YORK, SEPT. 12. The image of the World Trade Center's 110- storey twin towers crumbling seemed a scene of impossible destruction. But the steel and concrete architecture that made them could not withstand the power of Tuesday's attack and ensuing fire. No building designed today could, said Mr. Masoud Sanayei, a civil engineering professor at Tufts University.

Experts in skyscraper construction said video of the collapse led them to believe the towers were perhaps weakened by the initial impact of the airplanes that hit them, but that heat from the resulting fire was likely the most punishing blow.

Mr. Hyman Brown, a University of Colorado civil engineering professor and the Trade Center's construction manager, speculated that flames fuelled by thousands of gallons of aviation fuel melted steel supports.

``This building would have stood had a plane or a force caused by a plane smashed into it,'' he said. ``But steel melts, and 24,000 gallons (90,850 litres) of aviation fluid melted the steel. Nothing is designed or will be designed to withstand that fire.'' He said the towers were originally designed to survive powerful impacts, but that such construction could not make them fire or bomb-proof.

He said it appeared the attack was meticulously planned. ``If they did it lower in the building the fire department could have gotten to it sooner. In its simplicity, it was brilliant.''

Escape was cut off

The towers had staircases in all four corners and were designed to be evacuated in an hour, but it appeared that since the planes crashed into the corners, escape was cut off for those on the floors above, Mr. Brown said.

Mr. Sanayei said the heat may have disconnected one of the towers' concrete floors from the tubular steel columns that ringed the buildings. If one or two floors collapsed, it would have created a pancake effect of one massive floor caving into the next.

``In my opinion, the fire weakened the connection between the floor system and the columns on the higher floors and caused a couple of the floors to collapse,'' he said. ``The floors are very heavy, made of reinforced concrete, so when one hits the next, they cause a domino effect ... and it can go all the way down to the first floor.''

The glass and steel towers were the highlight of the career of Minoru Yamasaki, who was born in Seattle in 1912 and died in 1986. He worked with engineers John Skilling and Leslie E. Robertson to design the fabled towers. At the Detroit architectural company Yamasaki founded, there were condolences on Tuesday. Minoru Yamasaki Associates ``will provide any assistance we can to aid the rescue efforts,'' the company said.

``Words cannot adequately express the depth of our grief, and our thoughts and prayers go out to the victims and their families,'' the company added in a statement, declining further comment.

-AP

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