WHAT IS THE QUAKE RESISTANCE OF A TIMBER FRAME HOUSE?
Why lightweight wooden construction works better withstand an earthquake compared to brickwork and concrete
About the earthquake
An earthquake is the shift of the tectonic plates, at different depths inside the Earth, which is caused by geological phenomena, such as volcanic activity, and that produces vibrations in the form of seismic waves. These waves further create local surface field accelerations, where buildings and human-created infrastructure is located. The notion of an earthquake is used when the shift of the tectonic plates causes major damage, while the notion of seism is used for the movements that go unnoticed.
Romania is a high seismic potential country and has a history of major damage earthquakes that have caused the significant loss, the most recent ones are the one in 1940 ( 7,7 on the Richter scale) and the one in 1977 ( on the Richter scale). The most known seismic area in our country is Vrancea, where there is a continuous seismic activity and where an earthquake bigger the 7 on the Richter scale can occur at any time, at depths of 60 to 180 km. Despite all this, there are also other areas of seismic potential in the country, as highlighted in the map below.
Așadar, în România orice construcție, fie rezidențială, comercială, publică se proiectează în funcție de încărcările date de ocupanți, vânt, zăpadă, dar și de cutremur, conform prevederilor codului de proiectare seismică P100.
Timberframe resistance to earthquake
As previously mentioned, the shift of the tectonic plates creates seismic waves and, by default, local surface field accelerations that are further transmitted to buildings. The mass ( or in general terms, the weight of the building) is in direct ratio with the effects of an earthquake on a building, hence it is crucial in this context. The field acceleration alongside the mass of the construction turns into lateral inertia force. The bigger the mass of the building, the bigger the seismic force that acts against it.
At the first glance, you may have thought that a rigid concrete structure would offer more safety in the event of an earthquake, but things are different. A timber frame house, for instance, is 3-4 times more lightweight than traditional brickwork or concrete one, hence the effects of the seismic force are significantly lower. More than that, the loading on the foundation will be smaller and by default, its costs will be reduced. The wood itself is a resilient material and together with metallic joints (screws, corners, etc), they make a wooden construction better resist to Earth’s lateral shifts caused by an earthquake.
A relevant example that certifies the aspects mentioned earlier is a test on a 1:1 scale model: a 6-floor timber frame apartment building
Following the tests, the structure of the building has not been severely affected, except for the windows, indoor doors, and cracks in the cardboard gypsum pans on the inside. Other than that, due to the wood’s resilience, the structure of the building has not been compromised and it could still be used. Here you can find more details on the research project of 1.4 million worth.
Although in Romania, the Design norm NP 005 of 2003 allows the building of wooden building of no more than 3 floors (P+2), a wooden structure house be it timber frame, stick frame, or CLT, properly designed and built, will withstand any earthquake with flying colors, a situation which could occur in our country as well. Find out more about timber frame houses.