EARTHQUAKES
ADDITIONAL INFORMATION
FOR THOSE WHO WANT TO KNOW MORE ABOUT EARTHQUAKES AND THE SCIENCE BEHIND THEM
DYNAMIC LOADS CAUSED BY AN EARTHQUAKE
Wood’s natural elasticity, strength, and lighter weight give it an advantage during an earthquake. The natural ability of wood buildings to flex and return to their original shape in the event of an earthquake has made them a popular choice for centuries in regions prone to seismic activity (*). In some instances, historic centuries-old wooden buildings have remained nearly intact after significant earthquakes, while modern reinforced concrete and steel buildings have endured significant damage, or even collapse. Following earthquakes in Asia, reports indicate that wood structures best maintained their structural integrity and contributed least to injury and loss of life. And recent testing is showing that mid-rise light-frame wooden buildings up to three stories can endure a 7 magnitude seismic test with little damage. Low-rise buildings, with no second floor or more, will be able to withstand a 7.5 or even higher magnitude earthquake albeit with some damage.
(*) You can read more about this < here >
Damaging forces in an earthquake are proportional to a structure’s weight. Wood is substantially lighter than other building materials, giving it an advantage when paired with good seismic design. The fact that wood buildings tend to have numerous nail- or other metal connections means they have more pathways to dissipate the load (something known as load paths), so there is less chance the structure will collapse should some fail. This is what is referred to as ductility, a building’s ability to undergo large deformations without failing.
EARTHQUAKE ANALYSIS
If an earthquake analysis is required, our engineers will always calculate the natural frequency of the wooden house and compare this figure with the local codes and regulations as to the allowed ground motion. We apply a special finite element computer program to deal with the dynamic earthquake forces and design the building such that it can safely resist the seismic loads as prescribed by the locally issued seismic building codes. The seismic loads from the national codes are based on the concept of a Maximum Considered Earthquake (MCE). It normally combines both the results from probabilistic seismic hazard for a 2% probability of exceedance in 50 years (2500-year earthquake) and a deterministic approach in case of nearby active faults. The site-specific probabilistic seismic loads (spectral accelerations) can be derived from the seismic hazard maps of the country which form an integral part of the seismic building code. Based on the anticipated seismic loads a design spectrum will be specified for the site. Based on the anticipated seismic loads a design spectrum will be specified for the site. The seismic signals of relevant historical seismic events that have occurred near the area will be obtained and scaled and matched to the prescribed design spectrum. If these seismic signals are not available or usable, similar events from other locations in the world will be used, all according to the guidelines provided by the national seismic building code of the country. If the national building code of the country does not provide sufficient guidelines herein, the International Building Code (IBC) will be used instead.
We have supplied houses to earthquake-prone areas. So far no damage (*) has been reported after an earthquake struck.
(*) except for the falling off of several roof tiles