EARTHQUAKE RESONANCE AND NATURAL STRUCTURAL FREQUENCY
Earthquakes have minor influence, if not, no influence at all on a wooden building structure, due to its tremendous flexibility and strength. The seismic response of any wooden building is often amazingly high, this compared to a concrete or steel structure. The structural codes and regulations for countries or parts of countries which may be hit by an earthquake such as Japan, Indonesia, California, Hawaii, Mexico, Turkey, parts of the Caribbean, the Pacific and other areas, are defined such that the structure needs to be verified to its natural frequency (the number of vibrations per second) and be compared with the earthquake resonance (the frequency content of the ground motion). If this resonance is close or equal to the building's own natural frequency a building will suffer the greatest damage. And here plays the advantage of wood a significant role. The natural frequency capacity of a wooden building is often much higher than the earthquake response factor. However, as is always the case, there are limits. Economically it would not be an advantage to design a wooden house which can withstand an earthquake to a force which exceeds level 9 on the Richter scale. It's possible but far too expensive.
DYNAMIC LOADS CAUSED BY AN EARTHQUAKE
In the event that 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 as to deal with the dynamic earthquake forces and deisgn the building such that it should 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 forms 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 historic seismic events that have occurred near the site will be obtained and scaled and matched to the prescribed design spectrum. If these seismic signals are not available or not useable, 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, Eurocode 8 or the International Building Code (IBC) will be used instead.
We have supplied houses to earthquake prone areas. So far no damages were reported after an earthquake had struck.