Wood frame construction has superior seismic performance

Wood frame buildings are safer than concrete and masonry buildings in areas with a high risk of earthquakes. They save lives and reduce the cost of reconstruction.

Wood is strong, light and flexible. Wood buildings weigh significantly less than concrete buildings. This reduces loads on the structure, as well as the danger of heavy weights falling from above. The flexibility of the wood components allows the structure to deform and deflect momentarily in response to seismic forces without breakage, collapse or disconnection. Uplift and lateral loads are shared by the many wood members that make up the framework, the wood structural panels fastened to them, and the thousands of fasteners and connectors which tie the components together. This structural redundancy is stronger than predicted by conventional engineering analysis.

Additional measures can be taken in areas of greatest risk

In areas such as Sichuan, where severe earthquakes are likely, the structural design of a standard wood frame can be enhanced simply and inexpensively. Additional measures include braced walls, reinforced connections between foundation and floor, and walls to roof, as well as steel rod tie-downs that clamp the top wall to the foundation.

Scientists use the latest research as the basis for building codes

International scientists have been working closely with Chinese experts on seismic testing of wood frame building, using the shake test table facility at Tongji University. They aim to provide technical data on seismic performance. This will be used to develop building codes further, as well as to establish seismic safety design guidelines for wood frame construction and wood hybrid structures. The seismic intensities used for testing were comparable to the extreme earthquakes of California.

Tests show multi-storey hybrid structures can survive the most severe earthquakes

A full-scale, seven-storey mixed use condominium tower (six wood frame storeys above a one-storey steel structure) was tested. Conducted in Kobe, Japan, this was the largest full-scale earthquake test in the world. The building was subjected to a simulated quake that was 180 per cent of the Northridge earthquake in California, and suffered no significant damage. This demonstrates that even mid-rise wood buildings can survive the most severe earthquakes. The test used Japan's massive E-Defense Shake table, the largest shake table in the world.

There are solutions reducing the impact from earthquakes. Shock absorbing is the latest technology for earthquake protection of bridges and building constructions. An anti-vibration device - a panel with an anti-vibration unit - developed in Japan, for absorbing seismic energy in wooden constructions. When the force from an earthquake hits the construction, the energy is transformed via the panel to the shock absorber.

A survey of wood frame construction in severe earthquakes world-wide

The survey covers wood frame buildings of all ages and provides evidence of the superior safety of wood frame buildings in severe earthquakes world-wide, including Japan and the United States.

A very high proportion of wood platform frame buildings survived peak ground accelerations of 0.6 g and greater with no collapse or serious structural damage. The resulting injuries and deaths were few. There were very few specific failures, as for example from hillside collapses. Virtually all modern wood frame buildings survived with no visible damage.

EarthquakeRichter Magnitude MEst. number of wood platform frame houses "strongly shaken"Total number of casualtiesCasualties in wood platform frame houses
Alaska, 1964 8,4 - 130 < 10
San Fernando, California, USA, 1971 6,7 100000 63 4
Edgecumbe, New Zealand, 1987 6,3 7000 0 0
Saguenay, Quebec, Canada, 1988 5,7 10000 0 0
Loma Prieta, California, USA, 1989 7,1 50000 66 0
Northridge, California, USA, 1994 6,7 200000 60 16 + 4*
Hyogo-ken Nambu, Kobe, Japan, 1995 6,8 8,000** 6300 0**

* Foundation failure caused collapse of buildings on hillside.
** Relates to wood platform frame, known as ‘2x4' houses, in the affected area.

  • The Richter Magnitude Scale M is a commonly used measure of the overall size of the earthquake as determined by the total amount of energy released.
  • The maximum horizontal ground motion generated by earthquakes is measured by seismographs as a fraction of the force of gravity (g).
  • Very severe earthquakes can generate ground motions in excess of 0.6 g, but substantial structural damage can be caused at much lower levels. The Kobe earthquake was measured as high as 0.8 g.

A survey of wood frame construction following the Wenchuan earthquake, Sichuan

A survey was conducted following the tragic earthquake of May 12, 2008. The evidence showed that wood frame buildings had outperformed buildings constructed from other materials. They suffered only minor damage, while many brick infill walls collapsed and concrete buildings suffered severe damage.

In Dujiangyan, 40 km NW of Chengdu, about 21 km from the epicentre of the Wenchuan earthquake, many concrete and masonry structures were seriously damaged. Many collapsed, including three school buildings. Although not all the concrete and masonry collapsed, masonry infill walls were severely damaged, causing potential danger to occupants.

Reconstruction is now underway in the Sichuan area. Chinese authorities and specialists are working closely with Canadian and European counterparts in the support of the rebuilding, which includes houses, schools, and special facilities. These are permanent structures, meeting all building code requirements.

"The capability of a building to absorb seismic energy is a keypoint, in addition to the performance of its structural system. The damping of a steel structure is usually low. The damping of a concrete and brick hybrid structure is high, but the damping of WFC is even higher… WFC has performed well in many earthquakes and reduced casualties. There were a lot of traditional buildings that collapsed in the Wenchuan earthquake in May 2008, but wood frame buildings suffered no damage."

Prof. Lu Xilin, Dean of the Institute of Structural Engineering and Disaster Reduction, Civil Engineering College, Tongji University, March 2010

This is a good example of how light wood frame construction is proving to be cost-competitive in rural China, and responsive to local needs in regions where annual incomes are low. Moreover, these newly constructed wood-framed buildings are comfortable, energy-efficient, with lower annual energy costs, and resistant to severe earthquakes.

The full-scale earthquake test, Japan's massive E-Defense Shake Table, the largest shake table in the world
The full-scale earthquake test
Japan's massive E-Defense Shake Table
the largest shake table in the world
Shake table test, Tongji University, Shanghai
Shake table test
Tongji University, Shanghai
Site of Beichuan middle school tragedy, Sichuan
Site of Beichuan middle school
after earchquake, Sichuan
Wood-frame houses survived the Wenchuan earthquake with only minor damage, which could be easily repaired
Wood-frame houses survived
the Wenchuan earthquake
with only minor damage
which could be easily repaired
A shear wall of wood frame construction
A shear wall of
wood frame construction

 
European Wood (in China)
C412, Beijing Lufthansa Center
50 Liangmaqiao Road, Chaoyang District
Beijing, P.R. China 100125
T +86 10 6462 2066, F +86 10 6462 2067
info@europeanwood.org.cn
Sino-European Wood Center
Room 202, Engineering Department,
Taoliyuan Hou, Xuhui Campus of Jiaotong University,
No.655 Panyu Road, Xu Hui District, Shanghai
Tel/Fax:021-53098550
info@europeanwood.org.cn