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The shinbashira (心柱, also 真柱 or 刹/擦 satsu) is a central pillar at the core of a pagoda or similar structure. The shinbashira has long been thought to be the key to the pagoda's notable earthquake resistance, when newer concrete buildings may collapse.
The initial architectural forms included the pillar ingrained deep within the foundation ( Shinso ja: 心礎) Hōryūji Gojū-no-tou 法隆寺五重塔, (Gojū-no-tō: 5-layered-pagoda) was found to be 3m below ground level.
At this time, pillars were tapered and became roughly circular from the point where they rose beyond the roof, starting as hexagonal from the base. This shaping was necessary as metal pieces were fit to the central pillar to support the spire. Later uses starting 12c involve them suspended just above the ground, thus making them suspensions like the Nikkō Tōshōgū Gojū-no-tū 日光東照宮五重塔 (1818) in Tochigi prefecture.
Size had a bearing on the fragmentation of the pillars found in the 8th century. The central pillar of Gojuu-no-tou at Hōryūji has a height of 31.5 m with a diameter of 77.8 cm at base, 65.1 cm in the middle and approximately 24.1 cm at the midpoint on the spire. Such huge pillars had to be divided into three sections: from the base stone to the third floor; from the fourth story to the point where the spire begins, and the spire section. The shaft of a sanjū-no-tou is divided between the second and third stories and again where the spire begins. During the 8c, shinbashira were erected on a base stone set at ground level. Example: Hokkiji Sanjuu-no-tou 法起寺三重塔 (742) in Nara. (see Earthquake Resistance below)
Some of structural engineer Shuzo Ishida's model pagodas have a simulated shinbashira attached to the ground, as was common in pagodas built during the sixth to eighth centuries. Others simulate later designs with the shinbashira resting on a beam on the second floor or suspended from the fifth. Compared with a model with no shinbashira at all, Ishida finds that the one with a central column anchored to the ground survives longest, and is at least twice as strong as any other shinbashira arrangement. Studies about shinbashira and their quake resistant attributes have been many. These studies are now materializing even in brick-and-mortar buildings like the Tokyo Skytree. (see below)
More recently in San Francisco the renovation of 680 Folsom Street, a fourteen-story 1960s steel building, inspired an ultra-modern iteration of the shinbashira: an 8-million-pound structural concrete core that can freely pivot atop a single sliding friction-pendulum bearing during a large earthquake. Tipping Mar, the engineering firm behind the design, used performance-based design and nonlinear time-history analysis to prove that the solution would meet the goals of the California Building Code.See Putting a Good Spin on Value Engineering.
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