Christchurch Earthquake 2011
A structural engineer has compared concrete columns in the Canterbury Television building to pieces of chalk.
Rob Heywood, a forensic structural engineer from Australia, is the second Urban Search and Rescue member who assisted at the CTV site to give evidence to the Canterbury earthquakes royal commission today.
Heywood referred to witness statements that the CTV building collapsed quickly and "catastrophically", with many elements of the building become detached from each other, "possibly in a brittle manner".
He said that brittle structures provided no warning of collapse and often no opportunity to redistribute the load - much like a stick of chalk.
''One moment the chalk is carrying the load and the next moment it crumbles without warning," he said.
Columns could also behave in a brittle manner.
He said a building needed to be "ductile" to withstand a strong quake.
Combining concrete with steel gave a ductile result, but "if the bond between the steel and concrete fail, the building will fail".
Watch the CTV hearing live feed here.
The six floors of the building compressed into the height of a single-storey building, Heywood earlier told the commission.
Heywood arrived at the site at 4am on February 24.
His initial observation was that the building had largely collapsed vertically "in its own footprint".
The floors had become detached from the north core and collapsed. The south wall had then fallen and was lying on top of the rubble.
The floors had compressed to about 3.7 metres, or about the height of a single-storey building, he said.
Heywood realised early on that there would be an investigation into the building's failure.
He was concerned that a substantial amount of building material had been removed from the site already in the search for survivors.
Roof sheeting and concrete beams were piled in Madras St. Other material was taken to a location "unknown to me", he said.
Heywood took a photo diary of about 500 images between February 24 and March 4.
He said there had been "a large movement to the north" of concrete slabs and beams on the outside of the CTV building.
Concrete broke and reinforcement in columns failed.
Edge beams appeared to have become detached from the south wall on the lower levels and only some from levels 5 and 6 remained attached to the wall.
One beam fell on the car park next door.
Heywood said the concrete in the rubble disintegrated "more readily than I would have expected" during the recovery effort.
"It was surprisingly difficult for the machines to lift pieces of concrete without it breaking into pieces," he said.
"I considered this to be unusual."
Heywood said this was the same in all areas of the building, even in places not affected by the fire.
He urged the commission to "understand" issues on the tension strength of concrete in the building and if it was appropriate.
"I would encourage the commission to understand the concrete very closely," he said.
Cars linked to CTV fire
Crushed cars may have caused the building wreckage to catch fire, an inquiry has heard.
Structural engineer Graham Frost, the chief engineer for construction company Fletcher, assisted Urban Search and Rescue crews at the CTV building site after the February 2011 earthquake.
A fire that raged at the site after the building collapsed hampered rescue efforts.
Frost told the commission today that six burnt-out cars were removed from the internal car park during the recovery.
"I think it is possible that the fire may have started in these vehicles, providing a fuel source for some time," he said.
Frost spent five days at the CTV building site.
He arrived about 30 hours after the quake and immediately began documenting and storing debris to prevent its destruction.
Frost said he realised there would be "many lessons to learn" about how the building had performed in the quake.
"I felt I had an obligation as a professional engineer to try to capture details of this building's performance so the evidence would be available," he said.
Frost said that in his view the building was not well connected.
The concrete floor slabs did not stay intact and he saw no intact beam-column connections.
The beams separated from the columns "very early on", Frost said
"It points again to my belief the beam columns were a weak element," he said.
'A cloud of dust'
A man has described watching the CTV building disappear into a cloud of dust as he sat in his van clinging to the steering wheel.
Evidence from Matthew Ross opened the hearing today.
Ross gave his account of the building collapse - which claimed 115 lives in the February 22 earthquake last year - today as he was unable to yesterday.
Ross, the director of Window Coverings Ltd, was in a van in Cashel St driving west towards Madras St when the quake struck.
Concerned that a church he was beside would fall, he drove his van on to an angle and was still clinging to the steering wheel when the CTV building went down.
Ross said the building had been shaking side to side and back and forth.
The top of the building was bending towards Madras St.
He expected it would collapse in that direction, so he was "surprised when it began to drop straight down".
"I thought one of the bottom floors had given out,'' he said.
"I could see the top floors were intact as they disappeared into the dust.''
As the dust cleared, Ross saw people walking off the top of the rubble.
Police arrived and wanted everyone to leave the site, so he left in his van after about five minutes, he said.
He did not see any columns break or any smoke or fire.
The eight-week hearing will today hear witness accounts from Urban Search and Rescue members, including Rob Heywood, Graham Frost and John Trowsdale.
More than 80 witnesses will be called during the hearing, which will cover the initial building consent issued by the Christchurch City Council, the construction and design, identification of a structural weakness in 1990, and the assessment after the September 4 and Boxing Day quakes in 2010.
The commission has until November 12 to complete its work.
- © Fairfax NZ News
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