The report from the Federal Emergency Management Agency and the American Society of Civil Engineers also said the trade center's unique steel supports — called trusses — "may have played a role in allowing the buildings to collapse in the manner that they did." But the report said more study was needed before a final conclusion could be drawn.
Lawmakers at the Science Committee hearing where the report was formally unveiled Wednesday said more study was needed to make buildings safer.
"If we want to ensure that the legacy of this tragedy is that future building collapses are avoided or mitigated, we need to do a better job of investigating the causes," said Rep. Anthony Weiner, D-N.Y.
He and committee chairman Rep. Sherwood Boehlert, R-N.Y., took the wraps off legislation designed to better investigate building collapses.
The federal report said investigators detected no substandard structural problems at the trade center. In fact, the towers exceeded building code requirements in some areas, the report noted.
The report confirmed the consensus that barring a windstorm or an earthquake the twin towers could have withstood the impact of the two hijacked Boeing 767 airliners that plowed into the trade center on Sept. 11. The towers succumbed to the ensuing fire — fed by thousands of gallons of aviation fuel — that softened the buildings' steel framework.
"The fact that the structures were able to sustain this level of damage and remain standing for an extended period of time is remarkable and is the reason that most building occupants were able to evacuate safely," according to the report.
Still, the report said it was unclear whether engineering ever could protect buildings from fast-moving aircraft.
"Reliably designing a building to survive the impact of the largest aircraft available now or in the future may not be possible," the report said.
Professor Jonathan Barnett of Worcester Polytechnic Institute, one of the study's investigators, said the study proved overall the trade center performed well on Sept. 11.
"We didn't find a glaring blunder," Barnett said.
Still he conceded that the overall findings "could have a chilling effect on construction" of tall buildings.
The National Institutes of Standards and Technology is poised to take over the trade center collapse investigation, which it expects to take two years and cost $16 million. Institutes director Arden Bement said Wednesday he expected the results of his investigation "could lead to major changes in both U.S. building and fire codes and in engineering practice."
One key question will revolve around the trusses, the bracket-like steel supports which held up each of the 110 floors and provided lateral support to the skyscrapers' vertical columns.
Another will be whether fireproofing and stairwell safety recommendations for buildings "evaluated or designed for extreme events" should apply to structures generally.
The impact of the jets is believed to have blown off the fluffy fireproofing material on the trade center's steel columns, making them susceptible to the intense heat from ensuing fire. Fireproofing able to withstand such impact is used in U.S. Navy destroyers but the cost could be prohibitive, Barnett said.
In theory, the team found, occupants in the floors above the impact could have escaped had the stairwells been strengthened to withstand the attack and had the emergency escape routes not been placed so close together.
The two Boeing 767s slammed into the twin towers on the morning of Sept. 11. The north tower, struck first, stood for 102 minutes. The south tower fell 56 minutes after impact.
The suicide terrorist attack left 2,823 people dead or missing, though many thousands more escaped. Most of the victims were trapped in the floors above where the jetliners struck.
A large portion of the approximately 10,000 gallons of jet fuel in each plane was quickly consumed in massive fireballs that caused structural damage. But it was the remaining fuel that spilled across floors and down elevator shafts, setting ablaze furniture, computers, paper files and the planes' cargo over multiple floors and igniting an inferno.
