Factors in building collapse
The earthquake has caused collapse of more than 6.5 million buildings and damaged some 23 million more. Four factors determine the damage to a particular building, according to geologist Liu Jie (Chinese: 刘杰), Director of Earthquake Prediction Department of (China's) Center for Seismic Monitoring Station Network under the China Earthquake Administration (CEA), who arrived in quake zone the same day of the main quake. Besides the quake's magnitude and intensity in the area, the location of the building played an important role. In some towns that Liu surveyed, all buildings sitting on the earthquake fault line collapsed, while buildings tens of meters away did not. Building structure was also a factor. Buildings with larger spans tend to collapse more easily. The fourth factor was the quality of the building. If a building's designed fortification intensity is above the quake's intensity at the location, the collapse of a building can be definitively attributed to its engineering quality, Liu explained. On the other hand, if the quake's intensity exceeds the designated code, it would be hard to determine whether the earthquake engineering quality is the deciding factor of its collapse.
Modes of building collapse
Despite these factors, some Chinese civil engineers expressed a different view and joined the public in criticizing the initial official attribution of school collapses. According to Caijing, "earthquake intensity exceeding the designed resistance does not mean that buildings built to quality specifications will definitely collapse. Even if they collapse, there are different ways by which they collapse and variation within building design. Such collapses should not necessarily lead to heavy human casualties."
Buildings strictly built to the specifications of civil planning would not collapse during an earthquake. Any building that collapsed instantaneously must have failed to conform to civil planning standards. Either the design was unfit, or the engineering was unfit.
-- Liang Wei (梁伟), Executive Vice President of the Urban Planning Design and Research Institute of Tsinghua University
Seismic fortification for schools in the quake zone
A post-quake survey indicated the intensity near the epicenter of the earthquake to be category XI-intensity, far exceeding the seismic fortification intensity of VII-intensity assigned to Wenchuan, Sichuan in GB 500011-2001, a national standard for seismic design published in 2001. Beichuan, center of another XI-intensity area, had been zoned as VI-intensity. (Zoning for Wenchuan, Beichuan and several other cities in Sichuan were subsequently revised to VIII liedu, the second highest rating in the standard.)
GB50223-2004, the national standard for classification of civil seismic fortification before the earthquake, specified Class B for schools exceeding 600 in capacity, kindergartens and child care centers exceeding 200, meaning they must be built to at least 1 liedu higher than the zoned seismic fortification intensity of the area. However, it contained a provision to allow low-rise (three stories and lower) schools to be built to meet the area's fortification intensity (Class C). (The government rushed a revision to the standard after the Wenchuan earthquake. GB 50223-2008 has removed both the provision regarding capacity and the one regarding height to require all schools to meet Class B.)
In perspective, Yingxiu Primary School had a collapsed four-story building built in 1999, where 3/4 of the 473 students were dead, whereas Xuankou Middle School had several collapsed buildings from 3 to 4 stories built in 2006, where more than 80% of the 1,200+ students stayed alive. Both schools are located in the town of Yingxiu, Wenchuan nearly at the epicenter of the main quake. Beichuan Middle School in Beichuan, where 80% of buildings collapsed, had two collapsed five-story buildings completed in 1998 that were once named "high quality buildings," killing nearly half of its 2,000+ students. Following GB50223-2004, Xuankou Middle School should have been built to resist VII + I in seismic intensity. Beichuan Middle School and Yingxiu Primary School could have passed with fortification intensity of VII liedu had they been built after 2004; but because they were built before the publication of even GB 500011-2001, they could be using older standards or none at all.