Tokyo(1923 onwards) Aftermath of the Great Kanto Earthquake: Architectural changes
Wood has been a major component in Japanese architecture for as long as the Japanese had started building houses. In the Edo era, traditional housing, temples and castles were all made of wood. However, being extremely vulnerable to fire, most timber buildings were reduced to ashes in the fire following the Great Kanto Earthquake. More than 254,000 houses collapsed or were severely damaged, while 447,000 houses were burnt down. Furthermore, it is estimated that about 80% of victims lost their lives due to the collapse of wooden houses.
With the earthquake leaving so much destruction in its wake, it was evident that the current architectural conditions were not satisfactory. At that time, most wooden houses are built with traditional construction methods by carpenters, with little consideration for seismic resistance. The materiality of future architecture had to be reconsidered. Brick and masonry construction was out of question, as during that time it was unsafe against earthquakes and was prohibited by the Japanese government following the Nohbi earthquake. While timber buildings suffered collateral damage, it was revealed that more than seventy-five percent of reinforced concrete buildings survived with little to no damage, even though buildings were not designed to resist earthquakes at that time. (Figure 1) Thus, in the reconstruction of the city, although timber construction were still prominent, the Japanese started to build with more concrete and steel. Even with wooden buildings, there is additional reinforcement through the use of braces and nailed plywood or by reinforcing joints with metal components.
Figure 1: Damage of reinforced concrete buildings in Tokyo (Earthquake Investigation Committee, 1926)
Before the Great Kanto Earthquake, there was no legislation for architecture. Buildings were managed by their regional governors, regulated for purposes such as preventing conflagration in urban areas. The first Japanese building code, Urban Building Law was finally enforced in April 1919 to cover the six largest cities at that time, namely Tokyo, Yokohama, Nagoya, Kyoto, Osaka and Kobe. Under this building code, larger buildings could also start construction after handing in an application and getting permission from the police of each prefecture. Building height was also limited to 30.3m. Following the introduction of legislation, the Building Law Enforcement Regulations was introduced in November 1920, specifying structural design and requirements for building construction. The regulations required wooden beams to have a minimum thickness, reinforced concrete to have an earthquake load and for braces to be installed. In June 1924, the Urban Building Law Enforcement Regulations were further revised, this time requiring design of seismic forces to equal to 10 percent of the floor weight.
Building construction used to be a trade passed down from carpenters to their apprentices. Materials other than wood was uncommon as their construction method was so much different from the traditional Japanese timber construction. The Great Kanto Earthquake was one of the turning points for Japanese architecture, as it helped to realize the importance of structural engineering and hastened the need for building regulations. These regulations allowed for the stability of a building and is the first step of Japan towards earthquake disaster mitigation.
Clancey, Gregory K. Earthquake nation: the cultural politics of Japanese seismicity, 1868-1930. Berkeley: University of California Press, 2006.
Kidokoro, Tetsuo. Vulnerable cities: realities, innovations and strategies. Tokyo: Springer, 2010.