Engineers who attended the collapsed CTV building in the days after the fatal February earthquake in Canterbury, have described the 'catastrophic failures' of the building.
The Canterbury Earthquakes Royal Commission is looking into the failure of the Canterbury Television (CTV) building where 115 people died when it collapsed in a 6.3 magnitude earthquake on 22 February 2011.
Forensic structural engineer Robert Heyward told the Commission he was shocked to hear the pile of rubble he was working on had once been a six story building.
"The floors of the building had compressed into a pile of rubble of a height of a single story building, approximately 3.7 metres, and essentially we have the full building in here."
Mr Heyward believes the greatest number of people survived on level six because this was the only floor where concrete support columns remained intact.
Earlier, a civil engineer who helped with the rescue effort said the poor structure of the building's horizontal beams meant they snapped off their vertical supports.
Rescue worker Graham Frost, an internationally experienced structural engineer, spent five days in Christchurch after the February 2011 earthquake as a search and rescue engineer.
Mr Frost said he could immediately see how the building failed and he took careful notes, knowing there would be lessons to learn in the years to come.
Referring to photographs, he demonstrated to the Commission how, in his opinion, horizontal reinforcing beams broke away from vertical structural supports.
Mr Frost also said the weakness in the internal beams caused a pendulum effect during the quake, causing the floors to swing and snap away from vertical beams and the south wall.
He also said the fire that smouldered in the collapsed building may have started in cars parked underneath it.
Eyewitnesses say they saw smoke coming from the rubble of the CTV building within 10 minutes of its collapse.
Police abandoned hope of finding survivors more than 27 hours later.
Mr Frost believes the petrol in six cars parked underneath the building could have fuelled the fire for hours.
Builder shocked at damage days before collapse
Damage evident in parts of the CTV building days before its collapse has been described by a builder as the worst he had ever seen.
Builder David Bainbridge, who has had experience with large commercial buildings, said he noticed extensive damage on a visit a visit to the high rise with his wife six days before the February earthquake.
This included a number of cracks to a load-bearing column which Mr Bainbridge described as the worst he had ever seen.
In a statement read to the commission on Monday, Mr Bainbridge said flakes of concrete about the size of 50 cent coins had come away from the column and were lying around its base.
He expressed doubt at the time whether the column would hold up in another significant earthquake and said he could not wait to leave the building.
"I also felt so uneasy about being in the building, I could not wait to get out," his statement said. During the visit he remarked to his wife that he did not know how the building could have been signed off.