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Engineers prepare to assess damage after China's worst ever quake

Key roads cut off by landslides and collapsed bridges, isolating ravaged towns and hampering the relief effort in Sichuan.

Serious damage to vital road infrastructure was this week hampering efforts to provide emergency food and shelter to those caught up in the magnitude 8 earthquake that shook China’s Sichuan Province earlier this month.

The earthquake occurred in Wenchuan County in south west China’s Sichuan Province on 12 May. As NCE went to press, the latest figures indicated that over 40,000 people had died, 250,000 were injured and over 30,000 people were still missing.

The quake triggered numerous landslides in the mountainous province. It also damaged 33,333ha of farmland, including more than 10,000ha of wheat and rape and more than 20,000ha of vegetable fields.

Mountain roads connecting Chengdu the regional capital with the quake-hit zone were cut off by landslides, and bridges alongside and across the river Min were badly damaged. Other infrastructure hit included the concrete-faced rockfilled Zipingpu Dam (see p8) and countless public buildings.

"The road infrastructure has been damaged in two ways," said Hong Kong based Atkins director Patrick Ng.

"Some of the bridge panels between columns have dropped down onto the river bed. With those road sections cutting into the mountain sides, there have been major landslides. Large boulders have come down from the steep hillside, some are the size of half a house."

The damage has isolated many of the worst affected villages hampering efforts to get supplies in and people out. Efforts to bring in heavy lifting equipment to rescue trapped people and clear damaged buildings have also been hit. Some aid has been parachuted in by helicopter and people have been transported on the Min River.

About 5.36M buildings have been confirmed destroyed and more than 21M were damaged in the earthquake.Local news reports claim, over 80% of the buildings in Beichuan City have collapsed. The government is reported to be planning to preserve the town as a memorial and relocating its inhabitants.

Arup head of earthquake engineering Ziggy Lubkowski said that while modern Chinese design codes were comparatively strong by international standards, much of the building stock was built before the late 1970s, when these codes were developed.

"The modern Chinese codes are equivalent of the best of the West and are actually in front of Europe and America," said Lubkowski.

"On certain types of buildings, there is a two level design. The design has to show that there is no damage for smaller earthquakes and for bigger earthquakes there’s no collapse. In the United States and Europe we just design for loss of life.

"However, there are a lot of relatively old buildings in their building stock and it looks like the buildings that suffered were the ones built before codes of practice or before better monitoring," he added.

Ng added that in Beijing and Tianjing, high risk structures are designed to withstand magnitude 8 earthquakes.

"This earthquake, at 8.0 is already at the ultimate outer scenario," he said.

He also pointed out that not all buildings are designed to the same level as there are variations between regions according to geological and seismic data.

"The area around Sichuan has not experienced seismic activity for a long period of time," said the ICE’s local representative Chitr Lilavivat.
"The buildings in the area wouldn’t have been allocated high risk."

The Institution of Structural Engineers-backed Earthquake Engineering Field Investigation Team (EEFIT) has confirmed that it wants to send a team of engineers to Sichuan to investigate building and infrastructure damage. The investigation would help to improve understanding of structural behaviour under seismic loads and evaluate the adequacy of current design practices and regulations. Structures left standing are being assessed by Chinese government engineers.

"Ideally there will be a disaster management plan at local and district level where they [the Chinese authorities] will be checking critical facilities, communications, dams and checking them off the list or repairing," said Lubkowski.

"In the US, there’s a traffic light system, where one structural engineer will walk down one side of the road and one will walk down the other and will put a red, amber or green sticker on the buildings. A red one will mean that there is a serious problem and it needs to be pulled down, an amber one means that it needs a proper review and a green sticker means that it can be used straight away. Every country will have its nuances."

Ng remained less optimistic about the area which has been devastated by the earthquake.
"Virtually all buildings in the area are collapsed or unfit for occupancy. There are not many buildings left to be assessed as the majority are already collapsed."

Aftershocks still plague the region. Nearly 9,000 people were evacuated from Qingchuan on Tuesday following the appearance of 0.5m wide cracks in a nearby mountain. The mountain has sunk by up to 1m in places. It is feared that new aftershocks or heavy rainfall could trigger serious landslides.

"An earthquake on this scale happens more than you think" said Lubkowski.

"All around the world there is maybe one magnitude 8 earthquake or greater per year, there are 15 magnitude 7 to 7.9 on average and 140 measuring 6 to 6.9. These might occur in the middle of nowhere. It’s when it hits a populated area when there’s a problem. It’s not the earthquake that kills people; it’s the infrastructure that we build that kills people. The key is to design it adequately and construct it correctly."

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