Introduction

    After the 1995 Hyogo-Ken Nanbu Earthquake, many local governments in Japan had planed and implemented the improvement of their disaster measures against earthquakes and carried out the earthquake damage assessment in order to manage the risk due to earthquake disaster. In these assessments, many methods for estimation were adapted or developed, that correspond to local or regional characteristics of destructive earthquake.

    We have exhaustively surveyed the reports of these earthquake damage assessments, and picked up typical estimation methods for the risk assessment of buildings due to ground motion, liquefaction and ground failure. We, however, emphasize that other methods not introduced here are not considered inferior than the introduced ones. The methods introduced here are not for the estimation of damage on an individual building, but for that of the number of damaged buildings in the studied area.

    The risk assessment of buildings requires the results of the assessment of ground motion, liquefaction potential and geotechnical hazard, the methods of which have been described in the previous chapters.

    Here, we introduce some methods used in Japan, therefore strongly related with the structure of Japanese buildings and damage classification in Japan. The readers have to pay attention in that the availability of these methods are not assured or guaranteed for the application at outside of Japan where building types and characteristics are different from Japanese ones. These are just examples for the readers at outside of Japan.

    We explain the characteristics of the structure of Japanese buildings and the damage classification in Japan in the following.

    1. Structural type of buildings in Japan

      2. By tradition, wooden buildings are dominant in Japan. Almost all of non-wooden buildings in Japan are RC (Reinforced Concrete), SRC (Steel-framed Reinforced Concrete) or steel structures and there are few buildings that belong to other non-wooden types including masonry.

      Japanese buildings are constructed based on the building constructing code, which is determined and implemented by Japanese National Government, so that Japanese buildings have enough strength against ground motion and strong wind. The strength is dependent on the structure and the construction materials. The assessment methods are divided to some categories which correspond to the structure, the construction materials and others.

      Therefore, the assessment methods are introduced separately for wooden and non-wooden buildings.

    2. Building damage classification

      3. Japanese local governments investigate the extent of damage, when some buildings are damaged due to an earthquake. The number of damaged buildings is counted according to the damage classification which is based on the Disaster Relief Law in Japan. In the damage classification, the extent of damage is divided to some grades, which are called "Zenkai" and "Hankai". The summary of them is shown in Table 0.1. "Zenkai" means more serious damage than "Hankai".

      Other building damage grades, for example "Taiha" and "Chuha", are used in the field of construction engineering, which are based on other damage classifications. "Taiha" means more serious damage than "Chuha". The relative relationship between some building damage classifications are shown in Table 0.2, and it is said that the damage grade "Zenkai" is nearly equivalent to "Chuha" or more serious damage.

      Table 0.1 Summaries of the building damage grade "Zenkai" and "Hankai" based on the Disaster Relief Law in Japan

      Damage grade

      Summary

      "Zenkai"

      1. Loss of the fundamental function for habitation, or the damage is too serious for the building to be re-used as before by repair.

      2. Destroyed area is more than 70 % of all floor area.

      3. Economic loss is more than 50 % of main flame of house.

      "Hankai"

      1. Loss of a part of the fundamental function for habitation, or the damage is serious but the building can be re-used as before by repair.

      2. Destroyed area is 20 - 70 % of all floor area.

      3. Economic loss is 20 - 50 % of main flame of house.

      Table 0.2 Relative relationship between some building damage classifications

      Reference

Miyakoshi, J., Y. Hayashi and N. Fukuwa (2000) Relationship between damage ranks with different criteria based on building damage, Journal of structural engineering, 46B, 121-134 (in Japanese with English abstract).

Okada, S. and N. Takai (1999) Classification of structural types and damage patterns of buildings for earthquake field investigation, J. Struct. Constr. Eng., AIJ, 524, 65-72 (in Japanese with English abstract).