A team in Washington is sifting through materials that have already been gathered. NTSB is also examining the de-icing system that was installed on the bridge in 1997 and the chemical used in this system and what type of corrosive properties it might have.
"The finite element model of the bridge is being revised based on the measured deck thickness from core sections and physical examination of the bridge structure," said chairman Mark Rosenker.
"All structural elements have been incorporated in the model; however, some aspects of stiffness, weight and connections between elements are being modified to match the condition of the bridge the day of the accident."
Design records and details of modifications are being examined, and more than 300 witnesses to the collapse been inverviewed. Construction workers have also been interviewed and records have been examined detailing the quanitiy of materials on the bridge as part of maintenance work that was taking place at the time of the collapse.
Investigators are expected to remain on site until November.
