Abstract
Chuzu Temple is one of the buildings in the historical architectural complex in “The Center of Heaven and Earth” in Dengfeng County. It is more than 800 years old. Currently, various kinds of damage can be found in the Chuzu Temple main hall. For more applicable conservation and renovation of the building, the status of the dougong (斗拱) under the external eaves of the Chuzu Temple main hall was investigated. Additionally, the existing types of damage and their causes were statistically analyzed to provide a practical reference for structural performance evaluations and protection reinforcement of the extant structure. According to the investigation results, 50.8% of the dougong members under the external eaves of the main hall had different types of damage. The main types of damage included detachment, plucking, holes, cracking, crushing, separation, and missing parts. The main causes were mechanical damage, bioerosion, and material degradation. Additionally, the study revealed that Larix sp., Ulmus sp., Quercus sp., and Populus sp. were the wood species used in the restoration to replace the antiquated wood.
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Status Investigation and Damage Analysis of the Dougong under the External Eaves of the Main Hall of Chuzu Temple in the Shaolin Temple Complex
Ziyin Yao,a,# Yilin Que,b,# Xiaolin Yang,c,# Qicheng Teng,d Zherui Li,a Xiaolan Zhang,a Weizhen Cai,a Hongyi Lv,c Tongyu Hou,a Yifan Liu,a and Zeli Que a,*
Chuzu Temple is one of the buildings in the historical architectural complex in “The Center of Heaven and Earth” in Dengfeng County. It is more than 800 years old. Currently, various kinds of damage can be found in the Chuzu Temple main hall. For more applicable conservation and renovation of the building, the status of the dougong (斗拱) under the external eaves of the Chuzu Temple main hall was investigated. Additionally, the existing types of damage and their causes were statistically analyzed to provide a practical reference for structural performance evaluations and protection reinforcement of the extant structure. According to the investigation results, 50.8% of the dougong members under the external eaves of the main hall had different types of damage. The main types of damage included detachment, plucking, holes, cracking, crushing, separation, and missing parts. The main causes were mechanical damage, bioerosion, and material degradation. Additionally, the study revealed that Larix sp., Ulmus sp., Quercus sp., and Populus sp. were the wood species used in the restoration to replace the antiquated wood.
Keywords: Chuzu Temple; Dougong; Conservation; Restoration
Contact information: a: College of Materials Science and Engineering, Nanjing Forestry University, Nanjing, 210037 China; b: High School Affiliated to Nanjing Normal University, Nanjing, 210037 China; c: School of Architecture, Zhengzhou University, Zhengzhou, 450001 China; d: Baoguosi Ancient Architecture Museum, Ningbo, 315033 China; # these authors contributed equally to this work
* Corresponding author: zelique@njfu.edu.cn
INTRODUCTION
Ancient architecture is the crystallization of the wisdom of ancient artisans, and it has indispensable value in many areas, such as history and art. Ancient Chinese architecture is dominated by wooden structures, and one of its typical structural features is the use of a dougong between a beam and the top of a column (Li 2017). The dougong (known as puzuo in the Song Dynasty) is a unique structural element of interlocking wooden brackets and is one of the most important elements in traditional Chinese architecture. It is a structure installed under the eaves of ancient buildings or between girders that consists of two members, namely dous (斗, wooden block) and gongs (拱, bow-shaped brackets). Its main job is to transfer roof loads to the column frames and improve the seismic performance of buildings; additionally, it has architectural aesthetic functions (Ma 2003; Zhou et al. 2014). According to the location of dougong members in a building, they can be divided into two categories, i.e. inside eaves and external eaves dougong. Inside eaves dougong are found under the inside eaves of a building, and external eaves dougong are found under the external eaves of a building. The dougong is of vital importance for the timber frame structure of traditional Chinese buildings because of its unique functions (Que et al. 2015). The integrity of a dougong has considerable influence on the overall structure of a building (Tong and Liu 2018).
The concept of heritage conservation has been spreading, and increasing attention has been paid to the real-time monitoring, renovation, and protection of ancient buildings. An appropriate scientific renovation and reinforcement scheme should be based on an accurate understanding of the current status of a building. Therefore, site surveys have become an important part of the ancient building protection process (Chen et al. 2012; Zhang 2012; Chun et al. 2013).
The goal of this work was to contribute to a sufficient and reliable reference basis for the structural performance evaluation and restoration of the extant structure. The existing types of damage and their causes were analyzed. Information about the materials and their wood species (Cheng 1992; Kisternaya and Kozlov 2007; Yin et al. 2010; Mertz et al. 2014; Dong et al. 2017) was supplemented.
Experimental
Study Site
Chuzu Temple is located at the foot of Wurufeng Peak in the northwest of the Shaolin Temple complex (Guo 2009) in Dengfeng County. The overall scale of Chuzu Temple is not large. It is approximately 75 m long from north to south and 35 m wide from east to west. The main hall of Chuzu Temple (Fig. 1) is the main building in the nunnery. It uses a single-eave xieshan roof. According to records, Chuzu Temple was founded during the reign of Emperor Xiaowen of the Northern Wei Dynasty (A.D. 471 to 499), and was rebuilt during the Northern Song Dynasty in the seventh year of Xuanhe (A.D. 1125), only 25 years after publication of the treaty Yingzao Fashi by Li Jie (Wang 2003). The main original members and structural features have been retained after many restoration processes during the Jin, Yuan, Ming, and Qing dynasties (Qi 1979).
Fig. 1. Photo of the main hall of Chuzu Temple
In the 1980s, the National Cultural Heritage Administration of China appropriated funds to perform a survey and overhaul the main hall (Liu and Sun 2008). It has been approximately 40 years since the main hall was renovated. In the whole structure, the heavy roof loads eventually transmitted down to ground via the multiple-tier bracket complexes (shown in Fig. 2.), the intermediate horizontal and vertical components, and finally to the structural resisting beam-column components. Most structural members in the main hall of Chuzu Temple have been damaged to various degrees. Both the stone and wood have a certain degree of material degradation. To study the existing types of damage and their causes, the status of the dougong under the external eaves was investigated.
Fig. 2. Diagram of roof load transfer
Materials
There are 12 columns around the main hall of Chuzu Temple and four columns inside the hall. Each column has a dougong on the top (Zhang 2006; Yu 2016). The columns are made of stone. The dougong under the external eaves of the main hall were classified into three types: zhutou dougong (柱头斗拱, above the columns) (Fig. 3a)), bujian dougong (补间斗拱, between the columns) (Fig. 3c), and zhuanjiao dougong (转角斗拱, also called corner dougong under the corner of the eaves) (Fig. 3e).
To record information for each member clearly and conveniently, the dougong under the external eaves were numbered as presented in the column number index map of the main hall (Fig. 4a), and the dougong were numbered in the form of position-type. For example, A4-B4 East-south Bu means that it is a bujian dougong located between columns A4 and B4 on the southeast side. The names of the dougong members are shown in Fig. 4b.
Investigating the damage of the dougong under the external eaves of the main hall of Chuzu Temple was necessary. To provide an important basis for dougong reinforcement and restoration, the wood species were identified, and the wood material properties were tested. The ancestral temple has special historical value and protection regulations; therefore, the original wood that was replaced and preserved during the restoration of the main hall was selected for identification and testing. Because of the lack of an adequate systematic conservation and restoration process, the amount of remaining antiquated wood that was replaced during previous restorations of Chuzu Temple was limited. Chenghuang Temple on the west side of Wenmiao Street in Dengfeng City is in the same area as Chuzu Temple. It has a consistent architectural structure and wood material selection. Therefore, the antiquated wood of the structural members of Chenghuang Temple that was replaced during the repair process in December 2017 was selected for reference.
Fig. 3. Photos of the dougong under the external eaves: front view of zhutou dougong (a), side view of zhutou dougong (b), front view of bujian dougong (c), side view of bujian dougong (d), front view of zhuanjiao dougong (e), and side view of zhuanjiao dougong (f)