Abstract
The wooden columns in timber structures of ancient buildings have column foot tenons of various sizes. The main reason for these differences is their use for different roof loads. Six full-scale specimens with different sizes of column foot tenon were designed and manufactured. The tree species used for the specimens was larch. The quasi-static test was conducted on the specimens that were used in timber structures of ancient buildings. The effects of column foot tenon size on the mechanical properties of larch wooden columns were studied. The moment-rotational angle hysteretic curves, moment-rotational angle skeleton curves, ductility, stiffness degradation, energy dissipation capacity, slippages between the wooden column and the plinth, and the damage of the column foot tenons were examined. The test results showed that the column foot tenon played an important role in the mechanical behavior of the wooden column under low-cycle reversed cyclic loading. The rotation of the column foot tenon improved the energy dissipation capacity of the wooden column. As the rotational angle of the column base increased, the column foot tenon had different degrees of damage. Different sizes of column foot tenon had their own advantages and hysteretic behavior.
Download PDF
Full Article
Effect of Column Foot Tenon on Behavior of Larch Column Base Joints Based on Concrete Plinth
Xiaoli Han,a,b Jian Dai,b,c,* Wei Qian,b,c,* Baolong Li,d Yuanjun Jin,a,b and Ting Jiang a,b
The wooden columns in timber structures of ancient buildings have column foot tenons of various sizes. The main reason for these differences is their use for different roof loads. Six full-scale specimens with different sizes of column foot tenon were designed and manufactured. The tree species used for the specimens was larch. The quasi-static test was conducted on the specimens that were used in timber structures of ancient buildings. The effects of column foot tenon size on the mechanical properties of larch wooden columns were studied. The moment-rotational angle hysteretic curves, moment-rotational angle skeleton curves, ductility, stiffness degradation, energy dissipation capacity, slippages between the wooden column and the plinth, and the damage of the column foot tenons were examined. The test results showed that the column foot tenon played an important role in the mechanical behavior of the wooden column under low-cycle reversed cyclic loading. The rotation of the column foot tenon improved the energy dissipation capacity of the wooden column. As the rotational angle of the column base increased, the column foot tenon had different degrees of damage. Different sizes of column foot tenon had their own advantages and hysteretic behavior.
Keywords: Ancient timber structures; Wooden column; Larch; Column foot tenon; Hysteretic behavior; Concrete plinth
Contact information: a: College of Architecture and Civil Engineering, Beijing University of Technology, Beijing, 100124, China; b: College of Architecture and Urban Planning, Beijing University of Technology, Beijing, 100124, China; c: Beijing Research Center of Historic Building Protection Engineering, Beijing, 100124, China; d: Beijing Beiguo Construction Engineering Co., Ltd., Beijing, 100068, China;
* Corresponding authors: hanxiaoli221@emails.bjut.edu.cn; qianwei@bjut.edu.cn
INTRODUCTION
Ancient timber structures are an important component of Chinese culture and Chinese civilization. Ancient timber structures have been used for thousands of years (Chang et al. 2019), and they constitute a complete and independent structural system. The timber structures have extremely high research value, and they mostly have been built with wood in ancient Chinese buildings (Li et al. 2015). However, the timber structures of ancient buildings are inevitably subjected to various loading effects over time, such as earthquake actions and wind actions. Due to the long-term effect of these loads, the safety of ancient timber structures is often compromised.
The unique value status and special mechanical properties of ancient timber structures have attracted the attention and research of many scholars. A theoretical model of restoring the moment of the column foot joint was proposed, and the proposed model was verified with a finite element model (He and Wang 2018). A quasi-static test was used to study the appropriateness of the judging conditions for the uplifting of the plinth of ancient timber structures (He et al. 2017a). In addition, it was used to study the effect of high-diameter ratios (He et al. 2018) and different vertical loads (He et al. 2017b) on the mechanical properties of wooden columns. The non-linear finite element model of the column base joint (Wang et al. 2018) based on the rocking mechanism of the wooden column and the stress state of the column base was verified by a full-scale model with a pseudo-static test. The rocking characteristics of the first-class frame of ancient building timber structures under horizontal conditions were studied via a combination of theoretical derivation and finite element simulation (Wan et al. 2020). The shaking table test and the pseudo-static test were used to study the sliding motion between the wooden columns and the foundation stone and analyze the equilibrium relationship of the bending moment action of wooden column and restoring force characteristics caused by the column rocking of Japanese traditional wooden frames (Maeno et al. 2007). The quasi-static test was adopted for the traditional houses in southern Sichuan to study the lateral resistance provided by the masonry infilled Chuandou timber frames (Qu et al. 2020). A theoretical model of the rotational performance of the gapped Nuki joint that considered Hook’s law and Hankinson’s formula was established to predict the rotational stiffness and the initial slip of the Nuki joints (Shao et al. 2006). Shaking table and quasi-static tests were conducted on the wooden frame of Japanese ancient buildings without walls, and the horizontal restoring force was mainly determined by the bending moment resistance from tie beams and the restoring force due to column rocking (Suzuki and Maeno 2006). Local compression tests on a specified angle (Lee et al. 2009) on a wooden column in ancient Japanese buildings were conducted to study the skeleton curve of moment-rotation relation of the wooden column base. The results of the shaking table and static lateral load tests on the traditional wooden frame in Japan showed that the restoring force characteristics caused by the column swing and the bending moment of the tie-beam play an important role in traditional wooden structures (Kusunoki et al. 2003). Full-scale vibration tests and numerical analysis were used to study the sliding behavior of columns directly placed on flat stone foundations in Japanese traditional wooden buildings (Mukaibo et al. 2008).
Fig. 1. Types of wooden columns on the plinth
In previous studies, the wooden columns were placed directly on the pillar foundation. However, after reviewing the literature on the timber structure of ancient buildings and on-site investigation of the wood columns in ancient buildings, it was found that the wooden columns are not all placed in this way. The description of the column foot tenon is recorded in the relevant ancient architectural literature (Yunli 1734; Bai and Wang 2000; Ma 2003). There are three ways to place wooden columns on the foundation according to the ancient architectural documents (Ma 2003): (1) placed directly on the plinth (Fig. 1a); (2) placed on the column foot tenon (Fig. 1b); (3) placed on the touding tenon (“touding” is the name for a type of the column foot tenon in ancient timber structures.) (Fig. 1c).
Fig. 2. Plinth of Qing Dongling (Zunhua, Hebei, China)
Yunli (1734) described the wooden column foot tenon as follows: “each column is one foot in diameter, plus three inches of upper and lower tenons”. During the migration of Yongle Palace in the Yuan Dynasty (Bai and Wang 2000), it was found that there were tenons at the foot of the inner columns that existed in the Shanxi Province of China (The Institute for History of Natural Sciences 1985).
Secondly, the use of column foot tenons can be observed in the column foundation ruins of the ancient buildings on the site. Figures 3 through 8 illustrate the remnants of the plinth at the cultural relics site.
Fig. 3. Plinth ruins in the renovation of Nanjing Drum Tower (Nanjing, Jiangsu, China).
Fig. 4. Plinth ruins of Qing Dongling (Zunhua, Hebei, China)
Fig. 5. Plinth of Sima Jinlong tomb in Northern Wei Dynasty (Datong, Shanxi, China)
Fig. 6. Plinth of Shentong Temple in Sui Dynasty (Jinan, Shandong, China)
Fig. 7. Ruins of Panlong Plinth in the central capital of Ming Dynasty (Fengyang, Anhui, China)
Fig. 8. Plinth of Shentong Temple in Sui Dynasty (Jinan, Shandong, China)
In this study, six full-scale specimens with different sizes of column foot tenon were subjected to quasi-static loading to investigate the mechanical properties of the column base joints with column foot tenons. The tree species used for the specimens was larch. The details of the specimens, the experimental program, and the experimental results and analysis are reported in the following sections.
EXPERIMENTAL
Specimen Design
According to Figs. 1 through 8 and other preliminary works (Ma 2003; Ssu-Ch’eng 2006; BMCC 2007), six full-scale specimens with different sizes of column foot tenon were designed and manufactured. The details of six full-scale specimens are shown in Table 1. The different sizes of column foot tenons and plinth models are shown in Fig. 9. All specimens had a height of 2310 mm. The six specimens had a circular section of 210 mm in diameter. The height:diameter ratio of the specimens was 11:1. The depth of wooden column foot tenon was equal to the diameter of the column foot tenon, and the depth of CC-6 wooden column foot tenon was 3/10D.
Table 1. Test Data of Six Specimens
Fig. 9. Model of wooden column and plinth and column base joints
The use of the plinth in the Qing Dynasty is shown in Fig. 10. Plinth material was concrete.
Fig. 10. Use of the Plinth in Qing Dynasty
Material Properties
Larch was used as the wood for all specimens in this experiment, as it is representative of the tree species commonly used in ancient timber structures. The material properties of the specimens were tested according to GB/T 1938 (2009), GB/T 1936.1 (2009), GB/T 1935 (2009), and other relevant regulations. The data obtained from the material property tests are shown in Table 2, and results referred to defect-free small-scale specimens. The specimens are based on a water content of approximately 12% according to GB/T 1928 (2009).
Table 2. Test Values of Material Properties of Specimen
Methods
The experiment was conducted at the Engineering Structure Experiment Center of the Beijing University of Technology (Beijing, China).
A vertical constant load was applied to the wooden column head by a 150 kN horizontally free-sliding jack along the axis of the wooden column. The lateral jack was connected to the wooden columns through specially designed jigs to facilitate lateral load transfer to the columns. The loading device is shown in Fig. 11. The direction of the loading device model in Fig. 11 was referred to Fig. 13, and the horizontal actuator was in the east of the column.
The locations of the transducers are shown in Fig. 12, and the test loading site is shown in Fig. 13. The six vertical transducers (V1 to V6) were mounted to the side of the wooden column to measure the vertical displacement of the column. The lateral displacement of the column was obtained by seven horizontal transducers (H1 to H7). The lateral displacement of the column head was measured by the horizontal sensor H8. The original position of the column base was marked with blue before the test to observe whether the column base slipped during the test. If the column base slipped, the sliding position was marked with red.
Fig. 11. Loading device
Fig. 12. Locations of the transducers