In last week’s blog, the focus was on the symbolic value and usage of a pagoda artefact based on the Feng Shui belief. In the spirit of conducting an architectural investigation, I will further explore the pagoda in a more structural aspect – in the assembling of its joinery.
The art of joinery contributes greatly to the construction of a long-lasting freestanding pagoda structure. In Japan, all pagodas are primarily made out of wood; a significant feature for it reinforces their flexibility in sustaining the frequent earthquakes in Japan. The fall back in using wood for its entire structure is that the pagoda becomes extremely susceptible to fire. However, in using wood as a material relying merely on its joinery, fastening together the structural members by inserting carved thinner and narrower ends into slots, it eliminates the usage of nails entirely, allowing the wood surfaces in these joints to twist and rub against each other as they absorb seismic stresses.
The general posts and lintels structure of the pagoda starts with a square base at the bottom. As more stories are added to the base, the levels or tiers get progressively smaller and are structurally independent from one another. A central pillar, or shimbashira, standing on the base stone is extended up to the spire; however, it does not support the framework, roof, or any other parts of the structure. It is the inner and outer posts around the central pillar that are instrumental in supporting the weight of each story independently.
Typically, there are twelve pillars to each level known as gawabashira, which are enclosed by essentially a box with no bottom. The pagoda as a whole is, in essence, five stacked boxes. As the footprint of each level becomes smaller than the one beneath it, the placement of the gawabashira moves inward toward the center of the pagoda, supported and braced by horizontal beams. The pillars rest on these horizontal bases, which in turn are supported by diagonal beams known as taruki. The slanting beams run from the inside of the structure diagonally downward to the outside, where they support the eaves. Consequently, the large eave of each tier is supported by the portion of the taruki that protrudes from the pagoda with the eaves acting as a counterweight, balancing out the weight put on the taruki by the gawabashira that are supporting each level of the pagoda. The large roof of a pagoda, consisting of clay and tiles laid on top of wood rafters, is extremely heavy. A heavy roof relative to the size of the building is one of the main characteristics of traditional Japanese wood architecture. This then raises a serious concern. If each eave is supported by the level above itself, what happens to the eave that is located at the top of the pagoda? To solve this problem, a finial, or spire, made of copper or iron is placed at the very top of the pagoda, and is used as the counterweight for the uppermost eave.
All of these components together create a structure that provides layers of boxes that may sway slowly and swing independently of the others during typhoons and earthquakes, but almost never collapse. Pagodas were built not to resist the forces of nature head-on but to accept and absorb their impact; pagodas epitomize the ingenuity of traditional Japanese wood architecture.
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