Five years after the real thing, researchers at Purdue University in Indiana have simulated what likely happened inside the North Tower of the World Trade Center when American Airlines Flight 11 crashed into the structure on Sept. 11, 2001. The findings could help silence alternative collapse theory arguments.

The simulation provides a better understanding of which elements in the building's structural core were affected, how they responded initially to the collision shock, and how the tower later collapsed from the ensuing fire fed by thousands of gallons of jet fuel.

“The simulation enabled us to ‘look’ inside the building to see what happened structurally,” said Mete Sozen, a Purdue professor of structural engineering.

The Purdue work comes 11 months after the National Institute of Standards and Technology released its October 2005 technical investigation of the collapses.

Verdict on the NIST report was split. While most in the building design, construction, and fire and rescue fields embraced the three-year NIST effort and began working with NIST to use the report's 30 recommendations to improve building codes, standards and practices, others claimed that factors differing from those described in the NIST report brought the towers down.

However, NIST found no evidence that suggested the towers were brought down by controlled demolition using explosives placed prior to Sept. 11, or that missiles were fired at the towers.

Christoph M. Hoffmann, professor of computer science and co-director of Purdue's Computing Research Institute, said there is nothing in the Purdue results that supports alternative collapse theory arguments.

“When you lose a percentage of the core support and the exterior support structure, the remaining support beams have to make up the difference, and the increased load makes them more vulnerable to the effects of the fire that followed the impact,” Hoffmann said.