Seismic performance of wooden structures

  On December 18th, a 6.2-magnitude earthquake struck Linxia, Gansu, resulting in over a hundred deaths. The sudden collapse of houses and the passing of people have forced us to re-examine the seismic resistance of houses.

  It is understood that the main cause of casualties in earthquakes is the destruction and collapse of buildings. In the 1976 Tangshan earthquake, 70% to 80% of buildings collapsed, resulting in heavy casualties; In the 2008 Wenchuan earthquake, most of the casualties were killed or injured by collapsed buildings.

  Today we will share with you the seismic performance of wooden structures.

Why are wooden structures safer than concrete and brick structures in earthquake prone areas?

The self weight of wooden structures is much lighter than that of concrete structures, and they absorb less seismic force.

  The self weight of wooden buildings is only 12% -20% of that of concrete buildings. In earthquakes, the lighter the self weight, the smaller the inertia, and the smaller the horizontal load, which also reduces the amplitude of building shaking.

  Research has shown that for a two-story ordinary residential building with an area of 65 square meters on each floor, wooden, reinforced concrete, and iron frame buildings with the same building area will experience a horizontal external force of 30 tons for wooden buildings, 60 tons for iron frame buildings, and 150 tons for reinforced concrete buildings when subjected to earthquakes of the same intensity. The advantage of lightweight wooden structures is obvious.

The natural flexibility of wood effectively absorbs and consumes external forces.

  The lateral force generated by earthquakes can cause buildings to twist, causing walls to deform, resulting in breakage, collapse, or loosening. Compared with other building materials, wooden structures are uniquely endowed with good toughness and strong resistance to instantaneous impact loads and periodic fatigue damage. They can absorb seismic loads through brief deformation and force steering during earthquakes without directly breaking or collapsing, providing people with more escape time.

Wooden houses have relatively stable structures.

  Wooden structures are composed of hundreds of structural components and thousands of nail nodes connected together. If a force transmission path is damaged, the load it bears can be borne by adjacent components or nodes. Wooden houses have numerous transmission paths and are structurally redundant, providing additional safety during earthquakes.

Facilitating the implementation of rescue work.

  Wooden structures are mainly made of small-sized materials as load-bearing components, so they will not be directly fatal in the event of collapse. If rescue work is in place in the later stage, it can further reduce casualties. The light weight of wooden structures is also beneficial for subsequent rescue work, making it easier to open life passages for rescue.

  Moreover, after a typical earthquake, aftershocks continue to occur, and the environment may further deteriorate. The good elasticity of wooden structures makes them less prone to secondary collapse like other building structures.

  In the context of the global environmental community, it has become a consensus among countries around the world to construct more buildings through wooden structures, and multi story buildings will also be an inevitable trend in the development of modern wooden structures. We all know that the higher the building, the higher the demand for seismic resistance. Wooden structures have excellent seismic performance. Can multi story wooden structures still maintain such a high level of seismic performance?

  In order to test the seismic performance of modern multi story wooden structures, researchers at the University of California, San Diego conducted the Tallwood project seismic testing, which involved a 10 story wooden structure made of cross laminated CLT engineered wood.

  In this test, the mechanical vibration table simulated the 1994 Los Angeles 6.7-magnitude Beiling earthquake and the 1999 Taiwan 7.7-magnitude earthquake. The test results showed that modern multi story wooden structures still had impressive seismic performance in response to earthquake disasters: a 10 story wooden structure not only did not collapse during the earthquake, but also maintained the integrity of the overall structure.

  Through this experiment, researchers have collected key seismic foundation data for multi story and high-rise timber structures, providing data and theoretical support for designing higher timber structures in the future.

  Modern timber structures have excellent performance in earthquake resistance, wind resistance, and fire prevention. Nick Bevilacqua, the chief engineer of Fast+Epp, an international structural engineering company, stated that modern timber structures can withstand seismic forces 30% higher than ordinary buildings during earthquakes and can be designed as high importance buildings such as schools, hospitals, and post disaster shelters.

  In terms of structural innovation, Bevilacqua also pointed out that "modern timber structures can use CLT shear wall systems to achieve better seismic performance. This type of structure can transmit seismic loads through materials and components connected together, making the building more stable

  Human beings are fragile in the face of the powerful nature, but they are wise. By using appropriate building materials and plans, the harm caused by earthquakes can be effectively reduced. Wooden structure buildings can not only reduce casualties caused by earthquake disasters, but also have social and economic benefits. In the future, Xiaoyu Wooden House will continue to actively promote the application of wooden structure buildings, actively participate in the formulation of seismic standards for wooden structure buildings, regulate the wooden structure industry, promote the industrialization and marketization process of wooden structure, lead China's wooden structure towards the world's higher and larger development trend of wooden structure, and contribute to the construction of green cities.