Lesson Learned from Wenchuan Earthquake of 12 May 2008
ZHAO Bin*, TAUCER Fabio ** & LU Xilin*
*State Key Laboratory of Disaster Reduction in Civil Engineering,Tongji University, Shanghai 200092, China
**ELSA Laboratory, Joint Research Centre, European Commission, Ispra (VA) 21027 , Italy
Outline of presentation
• Earthquake characteristics• Affected region and field mission• Damage of buildings and infrastructure• Conclusion remarks on the damage• Code modification after the earthquake• Reconstruction and retrofitting issues• More discussion on the lesson learned
The earthquake
• 12 May 2008(2:28 PM local time)
• Latitude 31.0oN Longitude 103.4oEWenchuan countyof Sichuan Province
• Magnitude Ms = 8.0• Depth = 14 km
Epicentre of the quake
Beijing
Shanghai
The main event and aftershocks
The quake occurred in Longmen Mountain Fault Zone which marks the boundary of the Longmen Mountains in the joint area of Qinghai-Tibetan Plateau and the Sichuan Basin. The earthquake fault rupture started from the epicentre and travelled northwest, passing through Beichuan County and reaching Qingchuan County, resulting in an earthquake fault line with a length of about 300 km, approximately 3 times longer than the fault line of the M7.9 Tangshan earthquake of 28 July 1976.
Intensity map of the earthquake
The damage intensity in many of the most severely affected towns reached damage levels of X and XI, including Wenchuan County, Beichuan County, Mianzhu City, Shifang City, Qingchuan County, Mao County, An County, Dujiangyan City, Pingwu County and Pengzhou City, comprising a total area of approximately 26,000 km2.
by the China Earthquake Administration
Social and Economic consequences
• 69,227 dead with other 17,923 people being listed as missing and 374,643 injured.
• About 5.4 million buildings collapsed, 21 million buildings damaged
• At least 15 million people were evacuated from their homes, more than 5 million are reported to be homeless.
• The direct economic loss is estimated at RMB 845.1 billion (US$125.6 billion).
• ……
EEFIT and ELSA-JRC Joint mission on the Earthquake
The Earthquake Engineering Field Investigation Team (EEFIT) • EEFIT was formed in 1982• Affiliated with Institution of Structural Engineers, UK• A joint venture between industry and academia• 25 post-earthquake investigations undertakenThe Objective of the mission is to carry out a field investigations on the performance of Buildings and infrastructure in the earthquake area, as well as the socio-economic effects of the event and the disaster management procedure.Other two teams from JRC Ispra also had missions to China for the earthquake.
Team members and Towns visited (11 – 20 July 2008)
• Dr Matthew Free – Arup • Dr Fabio Taucer – JRC• Dr Bin Zhao – JRC• Dr Tizianna Rossetto –
University College London• Dr Navin Peiris – Risk
Management Solutions• Dr Xianfeng Ma –
University of Cambridge• Dr Jun Wang – Atkins• Mr Raymond Koo – Arup• Ms Enrica Verrucci -
ImageCAT
Field missions of Tongji University
• The first team reached the earthquake area on May 15, 2008, 3 days after the main event.
• Until October 5, 2008, Total 17 teams had visit to the earthquake area.
• On November 12, 2008, a book “The Wenchuan Earthquake Disaster”, which was edited by the State Key Laboratory of Disaster Reduction in Civil Engineering, was formally published.
• Tongji University has provided point to point technical support for the reconstruction and retrofitting work in Dujiangyan City.
• Up to now, many Tongji staffs are still visiting the area occasionally for the related scientific and reconstruction issues.
Yingxiu Town Destroyed by the strong ground shaking
Beichuan County Town, Destroyed by the combination of landslide and ground shaking
Beichuan Middle School
Classroom building built in 2003Classroom building built in 2003 Classroom building built in 1990sClassroom building built in 1990s
Two classroom buildings of Beichuan Middle School, before and after the earthquake
Reigu Towm
Leigu Town Destroyed strong ground shaking
Hanwang Town
Bell towerBell tower
HanwangHanwang Town is the most industrialized town in the seriously affected Town is the most industrialized town in the seriously affected area. The area. The DongfangDongfang Steam Turbine Works which is one of the three Steam Turbine Works which is one of the three biggest steam turbine producers in China, has moved out the townbiggest steam turbine producers in China, has moved out the town and and reconstructed their factories in the neighboring reconstructed their factories in the neighboring DeyangDeyang City.City.
Hanwang Town Destroyed by the strong ground shaking
Hanwang Town, Serious damage of an unconfined masonry street building
Hanwang Town..
Partial falling or collapse of school buildings / Bad quality of RC confinement
Serious damage or collapse of industrial building
Damage and collapse of historical building and structure
Benevolent Rule Memorial ArchwayBenevolent Rule Memorial Archway Temples at Temples at DoutuanDoutuan mountainmountain
Damage and collapse of the vernacular buildings
The structural wall changed from pure The structural wall changed from pure wood frame, wood frame with infill wall wood frame, wood frame with infill wall compose of clay brick or light concrete compose of clay brick or light concrete block, unconfined clay brick wall or light block, unconfined clay brick wall or light concrete block wall and even pure mud concrete block wall and even pure mud wall, while the roofs were made of wood wall, while the roofs were made of wood frames with lightframes with light--weight roofing tiles. weight roofing tiles. The light and unanchored tiles actually The light and unanchored tiles actually helped to reduce the seismic force to the helped to reduce the seismic force to the building by sliding or falling, most of the building by sliding or falling, most of the well built vernacular houses showed in well built vernacular houses showed in general quite good performance. The general quite good performance. The serious damage or collapse occurred serious damage or collapse occurred when the walls made of unreinforced when the walls made of unreinforced mud, brick or block. The slipping and mud, brick or block. The slipping and falling of the tilts were widely witnessed, falling of the tilts were widely witnessed, while structural damage of the roof only while structural damage of the roof only happened because of bad quality or happened because of bad quality or ageing reasons.ageing reasons.
Damage caused by rock falling
Damage to Damage to the road the road
deckdeck
Baihua bridge near Yingxiu Town
Xiaoyudong bridge near Xiaoyudong Town
Performance of dams and tunnels
circular crack
falling downof concrete
bulging collapseof road surface
collapse of pedestrainsidewalk (two sides)
upstream
Vertical settlement
80cm
downstream
Horizontal displacement
30cm
Destroy of electrical and industrial facilitiesDestroy of electrical and industrial facilities
Electrical tower Electrical tower collapse caused collapse caused
by combination of by combination of landslide and landslide and
ground shakingground shaking
Broken masonry Broken masonry chimney and steel chimney and steel
towertower
New 220 New 220 kvkv transformer station of the County, May 15 transformer station of the County, May 15 to July 12 reconstructed at same site.to July 12 reconstructed at same site.
Damage and collapse of electrical facilities and other infrastructure
Fully destroyed transformer station in Fully destroyed transformer station in YingxiuYingxiu Town Town
Conclusion remarks on the damage of buildings and
infrastructure
• The high levels of ground motion experienced in the affected area, which imposed demands as high as five to six times those stipulated by the current Chinese seismic design code GBJ 50011-2001. The poor construction quality of most building structures, both in terms of materials and seismic design, even in structures of recent construction which did not conform to the current Chinese seismic design code.
• The large stock of unconfined and unreinforced masonry buildings, as well as of reinforced concrete confined masonry buildings, which in the presence of irregular geometries, poor materials and inadequate detailing, offer low margins of safety with brittle modes of failure.
• The wide use of solid clay bricks for the construction of infill walls and non-structural elements, which due to their large weight, result in an increase of the forces induced by the earthquake.
• The frequent use of large openings at the ground floor of building structures to accommodate shops, commercial activities, parking and circulation of people, leading to the formation of soft-storey mechanisms.
Conclusions on the damage of buildings and infrastructure
• The bridges were seriously affected by the earthquake. The severe structural damage and collapse of the bridge structures resulted from the high ground motions and from the combination of strong ground motion with ground rupture.
• The transport service in the earthquake area was severely interrupted. Apart from the damage caused by the high levels of ground shaking, the earthquake induced landslides and rock fall constituted the main cause of the structural damage and functional failure of the road and railway network.
• Thousands of dams and waterworks, as well as tens of thousands of kilometers of water pipelines were damaged by the main earthquake event and aftershocks.
• The supply of electricity in the most affected cities and towns was interrupted due to the damage sustained by the transformer stations and to the collapse of the transmission towers.
Code modification after the earthquake
According to the findings from the earthquake area, the Chinese government promptly issued:
• updated version of “Standard for Classification of Seismic Protection of Building Constructions”.
• modified version of “Code for Seismic Design of Buildings”.The main modifications concern:• Seismic protection categories of buildings• Seismic zoning map• Construction site• Structural regularity• Structural robustness• Multi-protection line of structures• Structural staircases
MF 1: seismic protection categories of buildings
The Standard for Classification of Seismic Protection of Building Constructions classifies the seismic protection for buildings as four categories:
MP SP EP PP
• After the Wenchuan earthquake, the school building protection category is improved from SP to EP, including all class rooms, dormitories, and dining halls in kindergartens, primary schools, and middle schools. The principle is to protect those students who with no or less self-saving capacity during the earthquake.The modification means the structural details of school buildings will enhance one degree higher than that of the seismic intensity.For example, Shanghai locates in a seismic zone of intensity 7. School buildings in Shanghai will be controlled according to the structural details of intensity 8 instead of intensity 7.
MF 1: seismic protection categories of buildings
• The seismic zoning map is modified for the seventy earthquake-hit counties and cities in Sichuan, Gansu, and Shaanxi Province.
MF 2: seismic zoning map
The modifications include changing the seismic groups, increasing the design intensities and the design peak ground accelerations.
• From the damage experiences, it can be seen that, the specification of 200m is reasonable for the minimum distance of the construction site away from the active fault.
• The side slope design should regard to the geologic and topographical condition, and should avoid deep excavation and high filling. If possible, inclined slope and stepped slope are suggested.
MF 3: construction site
Photo from Prof. Y Yuan
• It is verified again in the Wenchuan earthquake, the buildings with irregular plan and elevation layouts suffered more serious damage than the regular structures. An irregular architectural scheme should be seismically strengthened; a particularly irregular architectural scheme need to be carried out specified studies to take corresponding measurements; and a seriously irregular architectural scheme should not be adopted.
MF 4: structural regularity
• Strong-column-and-weak-beam in frame structures: During in the Wenchuan earthquake, the concept design of strong- column-and-weak-beam was reproduced in a few cases, however most of damages happened in the pattern of strong-beam-and-weak-column.
MF 5: structural robustness
– The main reason is that the stiffness of the beam is enlarged because of the existence of the slabs and infilled walls above, whose effect is not considered in the current structural design.
1) One modification is to increase the amplifier coefficient of the column end bending moment, which will make the columns stronger.
2) The other is to reduce the reinforcement of the beams by taking the rebar in the slab, 6 times of slab depth, into the consideration of beam design.
MF 5: structural robustness
• Precast floor slabs and cast-at-site floor slabs: In the Wenchuan earthquake-hit region, pre-cast floor slabs are popular for its construction efficiency. However, lots of pre-cast slabs were found falling and rupturing in the event to cause unnecessary death.Cast-at-site reinforced concrete slabs are recommended. If precast slabs are applied, the structural measures both on the system and on the details should be taken to make sure the floor keep its integrity.
MF 5: structural robustness
• Constructional columns of the staircases: For the masonry structures, RC constructional columns and ring beams are configured to ensure the structural integrityMany staircases in masonry structures without constructional columns at the intercrossing walls were found to total collapse during Wenchuan earthquake. Constructional columns and ring beams are emphasized again in Chinese Code.
MF 5: structural robustness
During Wenchuan earthquake, single-span frames collapsed globally, while two- span frames stood still without entire collapse saved many lives.
Take Xuankou Middle School as an example. Although Building A collapsed in the aftershock, both Building A and Building B did not collapse in the main shock. Their performance saved the time for the evacuation of 1200 teachers and students.
In the 2001 version of Chinese Seismic Code, the concept of multi-protection line of structures has been included to avoid the progressive collapse due to the failure of the key members or components.
The concept is also emphasized in the seismic codes of USA (IBC, 2009), Japan (BSL, 2000), and Europe (Eurocode 8, 2009).
After the earthquake, it is modified in CSDB-2008 that, the multi-story frame structures with the height below 24 meters ought not to adopt single-span frames and the high-rise frame structures should not use single-span frames.
MF 6: multi-protection line of structures
Many staircase slabs damaged during the Wenchuan earthquake, so the Code enhances the design requirement for the staircase by including it in the structural analysis model and raising its structural ductility.
MF 7: structural staircases
Reconstruction of Yingxiu Town
Aerial remote sensing map by Chinese Academy of Sciences
May 24, 2008 May 21, 2009 April 27, 2010
Reconstruction of Beichuan County Town
Aerial remote sensing map by Chinese Academy of Sciences
May 16, 2008 May 16, 2009 April 18, 2010
Pictures of new Beichuan County Town Photo by Jiang Honhjing, Xinhua News Agency, May 11, 2010
Reconstruction and retrofitting
May 6,2009, Hanwang
Reconstruction and retrofittingMay 6,2009, Mianzhu
The application of new structural system and new technology. By now, the post-quake reconstruction of the earthquake-hit region has been performed two years. The concept of new seismic technologies has been applying to several cases. It is suggested that new technologies be widely used to enhance the seismic performance of buildings.
Reconstruction and retrofitting
Energy dissipation damper New wooden structural system
More discussion on the lesson learned
• Scientific work• Policy making• Education aspect• ……
May 6,2009
Better Life?Better Life? We need to put Safety First!Safety First!
Thanks for your attention!Thanks for your attention!
June 18, 2010June 18, 2010
