INVESTIGATORS AT the World Trade Center site say they have uncovered 'new and surprising' modes of structural element failure on low rise buildings around the twin towers.
The head of the American Society of Civil Engineers (ASCE) Pentagon and WTC investigations, Dr Gene Corley, told NCEI that one of the low rise buildings, WTC 5, had suffered 'unusual collapses' of floors due to failures at moment connections.
Corley said that while damage elsewhere in the building could have had an influence, this was 'a new type of failure' of beam/ column connections, and a loophole in fire resistance requirements for connections is under suspicion.
'In the US, there is no requirement for fire rating moment connections, unlike columns and beams. Our inquiries suggest connections do need fire rating, ' said Corley.
And the cause of the WTC7 Salamon building collapse, which fell hours after the twin towers, remains unclear.
'It is possible a fuel supply held in a City emergency centre located in the building could have assisted a fire which had already started, ' said WJE Engineers & Architects principal Kim Beasley. 'It is possible this could not be tackled by the fire service which was near breaking point after losing over 200 firefighters.' A gas leak is being discounted.
Corley also confirmed that his ASCE team only received detailed drawings of the twin towers in November after lawyers for the original owners, leaseholder Larry Silverstein and the structures' designers, finally agreed to requests for information.
'It has hampered us a little because we only have so many days before 1 March when the report is due, ' Corley said.