Why can the Yingxian Wooden Pagoda in Shanxi, which looks like a building block, stand for a thousand years?

Recently, a tower has become very popular on major social platforms - the Yingxian Wooden Pagoda. After a tourist posted a video of the Yingxian Wooden Pagoda on a social platform, it sparked heated discussions among netizens. Many people said: I was really shocked when I saw the Yingxian Wooden Pagoda, and the aftereffect was too strong......

Image source: A social platform

As the oldest and tallest existing pure wooden structure in the world, the Yingxian Wooden Pagoda is unprecedented and will never be surpassed. After all, in most people's impressions, traditional Chinese wooden structures are not tall, and most emperors' residences are only 10 to 20 meters high, while the Yingxian Wooden Pagoda can reach a height of 67.31 meters. When we face this "historical witness" engraved with the marks of all dynasties, it is indeed difficult not to be moved.

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How did such a tall and ancient wooden structure survive? Today we will talk in detail about the Yingxian Wooden Pagoda, which is one of the three most amazing towers in the world, along with the Leaning Tower of Pisa and the Eiffel Tower.

The structure of the Yingxian Wooden Pagoda is very complex

Regarding the Yingxian Wooden Pagoda, Mr. Liang Sicheng once said, "If you have not seen this pagoda, you don't know the extent of the possibilities of its wooden structure." Therefore, when talking about the Yingxian Wooden Pagoda, we have to mention its exquisite and ingenious wooden structure.

1

Double sleeve construction enhances stability

The Yingxian Wooden Pagoda adopts a unique double sleeve structure, which consists of an inner sleeve and an outer sleeve. The inner sleeve is used to enshrine Buddha statues, while the outer sleeve is used for Buddha worship activities. The inner and outer sleeves are connected vertically and horizontally through floor coverings, railings, beams, and rafters, forming a very stable frame beam structure.

Schematic diagram of the Yingxian Wooden Pagoda. Source: References

This structural system makes the various parts of the wooden tower closely combined, with a strong integrity, which greatly enhances the tower's ability to resist lodging. In addition, when the wooden tower is subjected to external forces, the rigid layer will produce inward tension, further enhancing the stability of the wooden tower.

2

Special floor design

The structure of the wooden pagoda is divided into two layers: the visible layer and the hidden layer, which are connected alternately. The visible layer is the Buddhist temple layer for worship, with an open space between beams and columns, which is the flexible layer of the structure; the hidden layer has many diagonal braces, which form many triangular structures, similar to modern truss structures, which are more stable and are the rigid layer of the structure.

This combination of rigidity and flexibility allows the flexible layer to play a certain buffering role when facing external forces, while the rigid layer can provide strong support.

The exterior and cross-section of the Yingxian Wooden Pagoda. Source: References

Under the action of upper gravity and the coordination of the rigid layer, the short and thick flexible layer columns have the ability to self-reset and can resist lateral forces such as wind or earthquakes, thus ensuring the overall stability of the wooden tower.

3

The exquisite function of the bracket structure

The bracket structure of the Yingxian Wooden Pagoda is a highlight of its architectural structure. There are 59 different types of brackets throughout the tower, with a total of 488 brackets in various combinations, earning it the reputation of "China's Historical Bracket Museum".

The brackets can not only share the weight of the columns, evenly transferring the huge weight of the roof to each column, reducing the pressure on the columns, but also buffer and disperse the external forces. When encountering external forces such as earthquakes, the mortise and tenon structure of the brackets can produce a certain deformation, consume the energy of the external force, and thus protect the main structure of the wooden tower. The existence of the brackets is like a "shock absorber" for the wooden tower, allowing the wooden tower to remain safe and sound in multiple earthquakes.

Building materials are also special

In addition, the main body of the Yingxian Wooden Pagoda is made of North China larch, and the brackets are made of elm .

The material of larch is hard, straight, corrosion-resistant, and has high strength and toughness, making it very suitable for building structures. The material of elm is hard and has good processing performance, which can meet the complex structural and process requirements of brackets. These high-quality woods provide a solid material foundation for the long-term standing of the wooden tower.

The craftsmen who built the wooden tower strictly processed the wood, including drying, anti-corrosion, and insect-proofing. The drying process reduces the moisture content of the wood, making it less likely to deform and crack; the anti-corrosion and insect-proofing can prevent the wood from being corroded and eaten by insects during long-term use, ensuring the quality and durability of the wood. These strict wood processing processes have enabled the wood of the wooden tower to maintain good performance after nearly a thousand years.

Key factors to surviving an earthquake

Historically, wooden pagodas are not easy to preserve, as they are either destroyed by fire, collapsed by earthquakes, or destroyed by humans. However, the Yingxian Wooden Pagoda has survived more than 40 earthquakes, more than 200 artillery attacks, and strong winds throughout the year, and has remained stable for more than 960 years.

Here, it is also worth mentioning that the foundation of the Yingxian Wooden Pagoda is made of clay and rammed stone.

Clay has good viscosity and plasticity, and can be closely combined with rammed stones to form a solid foundation. Rammed stones increase the bearing capacity and stability of the foundation, allowing the wooden tower to withstand huge weight. This foundation structure combining clay and rammed stones has good seismic resistance, can effectively disperse earthquake energy, and reduce the impact of earthquakes on the wooden tower.

The stone base of the wooden tower is 4 meters thick. The deep foundation can disperse the weight of the wooden tower and reduce the settlement and uneven settlement of the foundation. Even in the long-term use process, the foundation can maintain good stability, providing reliable support for the wooden tower. And when natural disasters such as earthquakes occur, the deep foundation can absorb and consume part of the earthquake energy, reducing the impact on the wooden tower.

In addition to the above, the geographical location of the Yingxian Wooden Pagoda also has a great impact on its preservation. Yingxian is located in the northern part of Shanxi Province, with a relatively dry climate and less precipitation, which is conducive to the preservation of wood. Less precipitation reduces the possibility of wood getting damp and decaying, extending the service life of the wooden pagoda.

However, according to past literature research, although the Yingxian Wooden Pagoda structure is earthquake-resistant, unfortunately, after years of impact, some components have begun to show signs of damage.

Now, the wooden pagoda has been twisted and deformed, but the maintenance and repair work of the Yingxian Wooden Pagoda has never stopped. Many experts are exploring more repair plans to ensure that the repair work is foolproof and buy more time for it. I hope that this only remaining wooden pagoda can eventually be preserved and continued with everyone's efforts.

References

[1] Chen Yukai. Research on the Characteristics of Brick-Body and Wooden-Eaves Towers in Suzhou and Hangzhou from the Late Five Dynasties to the Northern Song Dynasty[D]. China Academy of Art, 2014.

[2] Chang Zhaoqing, Zhou Linyi. Earthquake insurance helps protect the ancient wooden pagoda in Ying County[J]. Science, Technology and Industry, 2024, 24(18): 203-210.

[3] Li Yuhang. Research on structural status assessment method of large-scale tall ancient wooden buildings[D]. Southeast University, 2023. DOI: 10.27014/d.cnki.gdnau.2023.000109.

[4] Bai Xinyu. Scientific wisdom in ancient Chinese architecture[N]. Shandong Science and Technology News, 2024-05-15(003). DOI:10.28682/n.cnki.nsdkj.2024.000028.

[5] Lu Ya. It is said that the energy-dissipating and shock-absorbing design of the Yingxian Wooden Pagoda built by Lu Ban exceeds the modern level [N]. Shanxi Youth Daily, 2024-04-23(016). DOI:10.28761/n.cnki.nsxqn.2024.000762.

[6] Wu Yefan. Mortise and tenon: Wisdom hidden between concave and convex[N]. Science and Technology Daily, 2024-08-09(008). DOI:10.28502/n.cnki.nkjrb.2024.005034.

[7] Zheng Hongyu, Du Lijun. Exploration of tourism industry planning based on the protection restrictions of cultural relics and buildings[J]. Shanxi Architecture, 2019, 45(20): 21-23. DOI: 10.13719/j.cnki.cn14-1279/tu.2019.20.011.

Planning and production

Author: Zhang Daren, Master of Civil Engineering

Review丨Zhu Xuanxuan, Senior Engineer, Beijing Municipal Engineering Design and Research Institute Co., Ltd.

Planning丨Yinuo

Editor: Yinuo

Proofread by Xu Lailinlin