The Shinbashira (alt. Shimbashira ja:心柱), meaning "central tower", refers to a central pillar at the core of a pagoda or similar structure.
The word "shinbashira" is written as with the kanji 心 (shin, "heart", hence "central") and 柱 (hashira, "pillar") and follows Japanese rules of Sandhi where /h/ becomes /b/ after /n/ similar to Asahi ShinBun being Shimbun. It is also written with another character, hence 真柱; called satsu 擦, or 刹.
Hōryū-ji the world's oldest wooden structure, was found to have in 2001 a shimbashira from a tree felled in 594 AD  Their examples continue in impending centuries in other tō (塔, pagoda) like the Hokkiji in Nara in 8th century, and Kaijūsenji of Kyoto.
The pillar structure is made out of straight trunks of Japanese Cypress (hinoki). The pillar runs the entire (but see below) length of the pagoda, and juts out of the top 'layer' of the pagoda, where it supports the finial of the pagoda.
The initial architectural forms included the pillar ingrained deep within the  foundation(shinso 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 31.5m with a diameter of 77.8m 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 three-storied pagoda (sanjuu-no-tou 三重塔), 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 Sanjuuu-no-tou 法起寺三重塔 (742) in Nara. (see Earhtquake Resistance below)
Japan is an earthquake prone nation. Yet records show that only two of the pagodas have collapsed during the past 1,400 years owing to an earthquake. Hanshin earthquake in 1995 'killed 6,400 people, toppled elevated highways, flattened office blocks and devastated the port area of Kobe. Yet it left the magnificent five-storey pagoda at the Tō-ji Temple in nearby Kyoto unscathed, though it levelled a number of lower buildings in the neighbourhood.' The reason traditionally attributed has been the shimbashira; newer research shows that the very wide eaves also contribute to the inertial stability of the pagoda. Overall deductions have not been very simplistic 
Some of Mr 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, Mr 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 materalizing even in brick-and-mortar buildings like the Tokyo Skytree (see below) (see relevant links and citations for further reading on the other earthquake bearing of Japanese pagodas)
Pursuant studies of the Shimbashira structure, and its utility in quake-resistance has made it to be used anew in structures including the Tokyo Skytree. A central feature of the tower is a system to control swaying used for the first time, has been dubbed "shinbashira" after the central pillar found in traditional five-story pagodas. The 375-meter-long, steel-reinforced concrete shinbashira is not directly connected to the tower itself and is designed to cancel out the swaying of the needle-like tower during an earthquake.
More recently in San Francisco, the gut 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.
References and Further Reading
- "Why pagodas don’t fall down". The Economist Newspaper. The Economist Newspaper. Dec 18, 1997. Retrieved 12 March 2014.
- "100 YEARS OLDER THAN SUPPOSED?". Trends in Japan. Ministry of Foreign Affairs, Government of Japan. March 29, 2001. Retrieved 12 March 2014.
"The controversy [of the said pagoda being older than earlier thought] has arisen because a recent scientific examination of the shinbashira, the "heart post" that passes through the center of the pagoda, showed that the hinoki (Japanese cypress) wood used for this post was felled in A.D. 594. Assuming this timber was used shortly after it was felled, it means that the construction of the pagoda took place not at the beginning of the eighth century (around 711), as is generally believed, but about a century earlier. The generally held theory has it that Horyuji, including the pagoda, was first built around 607 by Prince Shotoku...quality of their construction is recognized by specialists throughout the world. In spite of the fact that the structure consists almost entirely of interlocking pieces of wood, the five-story pagoda has not succumbed to earthquakes, even though Japan is in a major earthquake zone
- "Structural Engineering in Action".
- Japanese Architecture and Net Users System (JANUS) http://www.aisf.or.jp/~jaanus/deta/s/shinbashira.htm
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- Vo Minh Thien, Do Kien Quoc, Yasuro Maki, Takanobu Nishiya (2010-04-15). "ON THE SPECIAL EARTHQUAKE RESISTANCE OF FIVE-STORIES TIMBER PAGODAS IN JAPAN (Tìm hiểu khả năng chống động đất đặc biệt của các ngôi chùa gỗ 5 tầng ở Nhật Bản)". Proceedings of the 1st Conference on Science and Technology(Kỷ yếu Hội nghị Khoa học và Công nghệ lần thứ (in English/Vietnamese). Retrieved 2014-03-14.
The special ability of earthquake resistance of five-stories timber pagodas in Japan remain a mystery up to now. In this paper, a typical five-stories timber pagoda is considered in which its structural model includes friction bearings connecting the central pillar (shinbashira) and footing, the surrounding pillars and beams of roof. The unclarity in structural details and connections of the pagoda are characterized by various parameters such as the gap between the shinbashira and floors, the coefficient of friction and the weight of roof. The non-linear dynamic responses of the pagoda with the proposed model and the traditional model are then analysed together according to ground acceleration of various earthquake records. The obtained results indicate that the proposed model gives much lower response compared to that of the traditional model. This analysis helps clear understanding on the special earthquake resistance of Japanese pagodas that remained for centuries
- Helston Science; Shuzo Ishida. "Structural Engineering in Action". Planet Scicast. Retrieved 12 March 2014.
- Tanimura, Akihiko; Ishida, Shuzo (1997), "Energy dispersion and dissipation mechanism of a Shinbashira-Frame system", Journal of Structural Engineering B 43B: 143–150, ISSN 0910-8033