Journal of Structural Engineering Vol.58A (March 2012) JSCE
Traditional construction technology of China timber arch bridges
Yan Yang*, Shozo Nakamura**, Baochun Chen***, Takafumi Nishikawa****
* College of Civil Eng., Fuzhou University, Fuzhou, China, 350108
** Dept. of Civil Eng., Nagasaki University, Nagasaki, Japan, 852-8521
*** College of Civil Eng., Fuzhou University, Fuzhou, China, 350108
**** Dept. of Civil Eng., Nagasaki University, Nagasaki, Japan, 852-8521
China timber arch bridge is a special bridge type, in which the arch ring is woven from two
polygonal arch systems. There are more than 100 such bridges survived in Fujian and
Zhejiang Provinces. Its traditional construction technology handed down from ancient to
today generation by generation through oral teaching has been listed in the Urgent
Safeguarding List of Intangible Cultural Heritage by UNESCO in 2009 because it is now at
a risk of disappearing. To record down the technique is one of the key issues to preserve the
intangible cultural heritage. This paper gives the general description of China timber arch
bridges and discusses their traditional construction technology.
Keywords: Timber arch bridge, China, Construction technology, Traditional,
Intangible cultural heritage
1. INTRODUCTION
Many timber arch bridges were built in history in many
countries, such as China, Italy, Belgium and Switzerland, etc.
However, only a few of them are remained now1) ,2)
.
The
authors classify the structural types of the existing timber arch
bridges into four types, i.e., timber rib arch, timber truss arch,
woven timber arch and the others3) ,4)
. Among them, only woven
timber arch bridges have been built in China. They are called
China timber arch bridges since this type bridges are only found
to be built in China5). China timber arch bridge achieves large
span by weaving longitudinal and transverse straight logs in a
special way. Conception of woven timber arch is ingenious, and
construction is convenient because members are light and needs
less processing.
China timber arch bridges are designed and built by bridge
craftworkers, and the technology has been handed down from
masters to their apprentices, in which many were done from
father to son and thus formed some timber arch bridge families
with stable characteristics in their construction technologies6).
However, there are only a few timber arch bridge craftworkers
alived with old ages today, and few young people like to learn
this skill because it is difficult to find a job. Therefore, the
construction technology of China timber arch bridges was listed
in the Urgent Safeguarding List of Intangible Cultural Heritage
by UNESCO in 2009 because this technology is at a risk of
disappearing. To record down this technique is one of the key
issues to safeguard this intangible cultural heritage. This paper
gives the general description of China timber arch bridges and
discusses their traditional construction technology.
2. GENERAL DESCRIPTION OF CHINA TIMBER
ARCH BRIDGES
According to historical records, the first China timber arch
bridge was built from 1032 to 1033 7)
. Thereafter, many such
bridges had been built in several places over the Fen and Bian
rivers in north China. The local people had great benefit by the
bridges, and called them rainbow bridges due to their arc shapes.
In this paper, this kind bridges are called as Bianhe Rainbow
Bridges. However, none of them survive and no details of their
design and construction technology have been recorded. The
structures can only be seen from a bridge in the famous painting
of “Chhing-Ming Shang Ho Thu” (Festival of Pure Brightness
on the River), shown in Fig.1, by Zhang Zeduan who is an artist
living in Northern Song Dynasty (1119 to 1125) 7)
. From the
painting, a sketch of the bridge structure was drawn as shown in
Fig. 2. It was estimated to be a 19.2 m long and 8-9 m wide
bridge with 21 groups of log arch frameworks arranged in
parallel.8)
This bridge technology was believed to be lost in twelfth
centrury. However, in 1970’s many similar bridges were found
in the mountainous areas in northeast of Fujian Province and
southeast of Zhejiang Province. Because they are all located in
Fujian and Zhejiang provinces, so they are called as Min-zhe
timber arch bridges, in which “Min” and “Zhe” is the short
name of Fujian Province and Zhejiang Province, respectively.
An investigation was carried out by the authors and the results
show that there are 128 Min-zhe timber arch bridges in use
today, as shown in Table 1. The distribution map is shown in
Fig.3.
In China it is quite common for a bridge to be dated to its
earlist construction time although the bridge may have periodic
maintenance and even an almost complete rebuild. In this paper,
the last rebuilt time is taken as the construction time but not the
earlist construction time. The maintanence and repair are not
considered as rebuilt and so do the relocation because the main
structure and members are remained as the original one. The
so defined construction time of the Min-zhe timber arch bridges
is listed in Table 2. It shows that most of the existing Min-zhe
timber arch bridges were built in Qing Dynasty, accounting for
53.91%, over half of the total.
The structures of Min-zhe timber arch bridge and the
Bianhe Rainbow Bridge are similar. Their main structures are
two longitudinal polygonal arch systems consisting of straight
logs. They are connected to the transvers beams by tennons. The
two systems with different polygonal sides are interlaced to be a
structure, in which the longitudinal members are mainly
subjected to compressive forces. However, the structure of the
Fig.1 Rainbow Bridge in Chhing-Ming Shang Ho Thu (Part)
6)
The first system The second system
21×45=945 40303030
6060
830
Fig.2 Sketch of the Bianhe Rainbow Bridge Structure 6)
Border of Fujian
and Zhejiang
Provinces
Fujian Province
Zhejiang Province
Fig.3 Distribution map of timber arch bridges
Table 1 Timber arch bridges in China
Province County Amount
Fujian
(83)
Shouning 19
Pingnan 15
Zhouning 9
Gutian 6
Fu’an 5
Zherong 2
Fuding 1
Xiapu 1
Fuzhou 1
Minhou 7
Minqing 2
Zhenghe 7
Jian’ou 5
Shunchang 3
Zhejiang
(45)
Taishun 11
Qingyuan 15
Jingning 15
Longquan 2
Qingtian 2
Table 2 Construction time of Min-zhe
timber arch bridges
Time Ming Dynasty
(1368-1644)
Qing Dynasty
(1644-1911)
The Republic
of China
(1911-1949)
Amount 4 69 26
Percent 3.13% 53.91% 20.31%
Time 1949-1965 1966-1999 Since 2000
Amount 15 0 14
Percent 11.72% 0 10.93%
Min-zhe timber arch bridge has some developments from the
Bianhe Rainbow Bridge.
A typical structure of a Min-zhe timber arch bridge is
illustrated in Fig. 48). It consists of abutments, arch ring, spandrel
structure, deck system and covered house, etc., while the lost
ancient Bianhe Rainbow Bridge did not have spandrel structure
and covered house. The Min-zhe timber arch bridge with the
side-covering boards looks like a three-line polygon and had
been considered as strut-framed bridge for a long time. Such a
configuratoin shows a large difference from the uncovered
Bianhe Rainbow Bridge shaped in arc with the extrados stepped
for pedestrians. The covered house can prevent decaying due to
abundant raining in this area and can also add the structure
self-weight to light timber arch structures, so that they improve
resisting capacity against up-lift loads from winds and torrents.
Various covered houses make the existing timber arch bridges
rich and colorful in their appearances (Fig.5) 6),10)
.
Arch ring of the Min-zhe timber arch bridge has X-bracings,
which can improve its transverse stability and stiffness. In
general, long span bridges have two sets of X-bracings, while
short span bridges have only one. Moreover, the joints in the
longitudial system are different. The logs of the Bianhe
Rainbow Bridge was binded together by ropes as shown in
Fig.6, while mortise and tenon nodes are used in the Min-zhe
timber arch bridge as shown in Fig.11.
Fig. 7 is an example of the Min-zhe timber arch bridge--the
Wan'an Bridge. It has a width of 4.7 m and a total length of 97.4
m with 6 spans and 5 piers made by granite. The bridge was first
built in 1090, and rebuilt three times in 1845, 1932 and 1953.
The first system of the arch is a three-line polygonal arch ribs
with nine parallel members connected by two transverse beams
at the two knees (Fig.7(c)), and the second system is a five-lines
polygonal arch ribs with eight parallel members connected by
four transverse beams at the four knees (Fig.7(d)). A photo of up
view of the arch is shown in Fig.7 (e). The length of the longest
span of the bridge is 15.3 m and the shortest one is 10.6 m, and
every span of it has one set of X-bracings, as shown in Fig. 7 (f).
3. TRADITIONAL CONSTRUCTION TECHNOLOGY
Since no construction method and technology of the Bianhe
Rainbow Bridge has been recorded down, only the traditional
Fig.4 Sketch of Min-zhe timber arch bridge 12)
Fig.5 Timber arch bridge with covered house
Fig.6 Binding node of Bianhe Rainbow Bridge
the transverse beam of the first system
the spandrel structure (horse-leg)
the longitudinal beam
the X-bracing
the second system of the arch ring
the frist system of the arch ring
the transverse beam of the second system
the rails
the covered house
the transverse beam of the second system
Covered house
Spandrel protection plates
Transverse beam of 2nd system
Transverse beam of 2nd system
Transverse beam of 1st system
2nd system of arch ring
1st system of arch ring
X-bracing
Spandrel structure
(horse-leg) Longitudinal beam
construction technology of the Min-zhe timber arch bridge is
introduced. The construction process includes the following five
steps: (1) Selection of bridge location; (2) Construction of
abutments and piers; (3) Treatment of logs; (4) Erection of arch
ring; (5) Construction of spandrel structure and covered house,
etc11), 12)
.
3.1 Selection of Bridge Location
In the traditional Chinese society, just as other construction
engineering activities, building bridge also has some important
religious rituals and folk beliefs behavior. Selection of a bridge
location is generally followed the Fengshiu (wind and water) to
meet a quest for an auspicious location. Many Chinese timber
arch bridges are located at the site called Shuikou (the mouth of
water), the downstream of a river of a village, according to the
Fengshiu13)
, which could bring peace lives and prospects for the
local people. However, selection of the bridge location by
Fengshiu does not mean it has no consideration of bridge
construction condition. It can be found that some consideration
of the site hydrological and geological conditions is hided in the
rules of Fengshiu.
In many China timber arch bridges,the arch ribs are directly
stand in natural cliff and crag with shallow carves without an
abutment, as shown in Fig. 8 and Fig. 912)
. This shows that the
craftworkers have rich experience, high techniques and wisdom
in selection of bridge location. Many China timber arch bridges
survived can be seen as a proof of the reasonability of the
traditional site selection method.
Fig.8 Abutment of Ruanfeng Bridge
12)
Fig.9 Abutment of Fushou Bridge12)
(a) Side view (b) Covered house
(c) First system (d) Second system
(e) Up view of the arch (f) X-bracings
Fig.7 Wan'an Bridge
3.2 Construction of Abutments and Piers
Elevation measuring is the most important process during
the construction of a timber arch bridge. However, there was no
advanced equipment for surveying at past, so craftworkers
invented a simple and effective way to measure, i.e., utilizing a
half section bamboo pipe filled with water in which the knots
have been cut off, as shown in Fig. 10. If the bamboo is not long
enough for the bridge span, several bamboo may be used with
temporary supports. The bamboos are connected by covering
each other some length and sealed with yellow wet clay in the
joint bottom to prevent the water seeping out11),12)
. The level
could be reached by adjusting heights of the bamboo in the
supports.
Beside some bridge utilizing the natural rock as arch seats as
illustrated in Fig. 8 and Fig. 9, most abutments of the bridges
were built by big gravels or block stones. Piers in multi-span
bridges were also built by block stone with spread foundation.
These structures were all built by manual method as other
masonry structures and no special techniques should be
described herein.
3.3 Treatment of Structural Members
Trees with suitable sizes in local area are selected as the
bridge materials. After cut down and transported to bridge site,
simple treatments are conducted according to the design of craft
master.
The bridge is built without nails and ropes, and all the
components are joined with various mortise and tenon joints.
The main arch ribs are joined with the straight tenons and the
Swallow Tail tenons shown in Fig 11. Generally, the latter is
used for joints which need certain resistance against tension.
Construction of all structural members is completely
processed by manual operation. They are all made by traditional
tools, such as the Luban rulers, carpenter’s ink markers, wooden
fork horse, axes, chisels, planers, saws, etc. They are shown in
Fig. 12.
3.4 Erection of Arch Ring
During the whole process of construction of a timber arch
bridge, erection of the arch ring is the most important process.
The four steps for a single span bridge illustrated in Fig.13 are as
follows: (1) Standing vertical columns in the abutment as
elevation scales; (2) Erection of the first system (three-lines
polygonal arch ribs); (3) Erection of the second system
(five-lines polygonal arch ribs); (4) Installation of the
X-bracings12)
.
The main primitive machine used for erection of the arch
Fig. 10 Measuring the level
12)
1 1 1 1
222
1 1 1 1
222
(a) Mortise and tenon joint (b) Mortise
(c) Straight tenon (d) Swallow Tail tenon
straight tenon
Swallow Tail tenon
transverse beam
longitudinal member
longitudinal member
(e) Schematic diagram
Fig.11 Mortise and tenon joint
(a) Luban ruler (b) Carpenter’s ink marker
(c) Wooden fork horse (d) Axe
(e) Chisel (f) Planer
Fig.12 Treatment of timber members with traditional tools
rings is a wood winch as shown in Fig.14. It is used to erect log
members in arch ring and bracket for supporting the members
during construction.
Two brackets located near the two knee position of the first
system are built as shown in Fig.15 in order to support springing
members of the first system erected by wood winches (Fig.16).
The bracket is made of two main columns, a cross beam and
several diagonal strut members.
After all the springing members (see, Fig.17) in the first
system have been erected in position, two transverse beams are
hoisted up (Fig.18), and tenon joints of the members are inserted
into straight mortises of transverse beam. All the members in
one side are jointed together and form two frames laid on the
brackets. Then the crown members are inserted into the Swallow
Tail mortise of the transverse beams to unite the two springing
frames together and form three-line polygonal arch ribs as
shown in Fig.19.
The second system of the five-line polygonal arch ring is
easier to erect after the first system is completed. The arch
members of the second system are placed on gaps of the
members of the first system and erected from the springing
members to quarter members. When all the crown members are
installed to close the arch (Fig.20), the second system is
completed and the basic arch structure of the bridge has been
formed. There is no direct and structural connection between the
two systems. In other words, they are basically independent.
Fig.14 Wood winch
Fig.15 Bracket12)
Fig.16 Lifting arch ring members12)
Fig.17 End of springing members
Vertical columns
in the abutment
Vertical columns
in the abutment
The first system consists of seven or nine three –lines
polygonal arch ribs and two transverse beams
The first system consists of seven or nine three –lines
polygonal arch ribs and two transverse beams
The second system consists of six or
eight five-lines polygonal arch ribs
and four transverse beams
The second system consists of six or
eight five-lines polygonal arch ribs
and four transverse beams
Short span bridges with only one
group of X-bracings
Short span bridges with only one
group of X-bracings
Fig.13 Process of erection of the arch ring
It should be pointed out that punner and hammers made of
wood instead of iron or steel are employed as common tools in
construction of China timber arch bridges, as shown in Fig.21,
to prevent serious damage of the wood members during
construction.
The last step to complete the arch ring is to install
X-bracings shown in Fig.22. One side of the X-bracings is
inserted into transverse beams with the Swallow Tail tenon, and
the other side is inserted into vertical columns in an abutment
with a straight tenon. Finally, wood blocks are inserted between
springing members as shown in Fig.23. They will provide a
local contact for them to enhance the integrality of the arch ring.
3.5 Construction of Spandrel Structures and Covered
House
A bridge deck system consists of deck transverse beams,
longitudinal beams and deck slabs. Generally, there are six deck
transverse beams (each side of three), in which the one close to
an abutment is supported by columns as shown in Fig.4 and the
transverse beam near the crown utilizes the transverse beam in
the second arch ring system. Only the deck transverse beam in
quarter span needs spandrel struts to support it. This spandrel
struts, called as horse-leg in Chinese Folk, consist of a pair of
inclined members standing on the springing and two or three
vertical or inclined members standing on quarter transverse
beam in the second system, as shown in Fig. 24.
A covered house is similar to a local general house and is
built from the central part to two side parts (Fig.25). Names of
craft masters and their chorography and pedigrees are written on
the ridge of the covered house for recognition of their
participation and contribution (Fig.26). Raising of the ridgepole
(Fig.27) is a high point in building the covered house with a
ritual as in houses and temples in Chinese traditional
folk-custom13)
. Since building the covered house is similar to
build a house in the local area, no special techniques should be
described herein.
After the bridge is finally completed, a ceremony of
completion will be hold in an auspicious day and then the bridge
is open to public use.
Fig.18 Installation of transversal beam
12)
Fig.19 First system
Fig.20 Installation of crown members12)
(a) Punner (b) Hammer
Fig.21 Wood Punner and Hammer
Fig.22 X-bracings12)
Fig.23 Blocks
Fig.24 Horse leg
4. CONCLUDING REMARKS
China timber arch bridges are essence of architectures in
China and even in the world. The traditional construction
technology is a precious intangible cultural heritage handed
down from ancient people. It is the key issue in maintenance of
the existing bridges and building of new timber bridges, and
could also be a reference to create innovative construction
technique for erection of modern arch structures. As time passes,
this technology is now at a risk of disappearing and needs urgent
safeguarding. Recording the construction technology may bring
benefit for technology learning and absorbing more young
people to learn it to prevent its disappearing in our generation.
This paper only gives the general description of China
timber arch bridges and discusses the traditional construction
technology. The FE analysis, the structural parameters analysis
in existing bridges and the others will be conducted in the future
work.
References
1) Leonardo Fernandez Troyano, Bridge Engineering—A
global Perspective. Thomas Telford, 2003
2) Carla Ceraldi, Ennio Russo Ermolli, Timber Arch Bridges:
a Design by Leonardo, Proceedings of Arch Bridges
IV--Advances in Assessment Structural Design and
Construction, Barcelona, Spain, pp. 69-78, 2004
3) Baochun Chen, Yan Yang, Introduce Foreign Timber
Arch Bridge, Proceedings of the Third China International
Symposium on the Covered house Bridge of Timber Arch
Structure in Pingnan, Pingnan, China, pp.237-241. 2009
(in Chinese)
4) Yan Yang, Baochun Chen, Comparative study on the
timber arch bridge in China and abroad, Proceedings of the
Third Chinese Colloquium on Ancient Bridge, Nanjing,
China, pp.103-110, 2010 (in Chinese)
5) Baochun Chen, Yan Yang, Several Issues on China
Timber Arch Bridge Protection and Research, Proceedings
of the Second Chinese Colloquium on Ancient Bridge,
Fuzhou, China, pp.18-26, 2009 (in Chinese)
6) Yan Yang, Baochun Chen and Jing Gao, Timber Arch
Bridges in China, Proceedings of the Fifth International
Conference on Arch Bridge, Madeira, Portugal,
pp.171-178, 2007
7) Huangcheng Tang, Chinese Ancient Bridges, Beijing:
Cultural Relics Press. Beijing, China, 1957 (in Chinese)
8) Yisheng Mao, History of Technique of Archaian Bridges in
China, Beijing Press. Beijing, China, 1986 (in Chinese)
9) Huangcheng Tang, History of Science Technology in
China, Bridge Volume. Science Press. Beijing, China, 2000
(in Chinese)
10) Jie Liu, Weiping Shen. Lounge Bridges in Taishun.
Shanghai People’s Fine Arts Publishing, Shanghai, China,
2005 (in Chinese)
11) Hongfeng Yao, Difa Gong, The construct technology of
the timber arch bridge in Fujian, Traditional Chinese
Architecture and Gardens, pp.11-16, 2007 (in Chinese)
12) Yan Yang, Baochun Chen and Jing Gao, Construction
technology of the timber arch bridge in China, Proceedings
of 2nd Chinese-Croatian Joint Colloquium on Long Span
Arch Bridges, Fuzhou, China, pp.341-349, 2009
13) Ronald G. Knapp, Peter Bol, A. Chester Ong, Chinese
Bridges: Living Architecture from China's Past, Tuttle
Publishing, America, 2008
(Received September 14, 2011)
Fig.25 Building covered house
Fig.26 Ridges of the covered house
Fig.27 Sacrificial rites12)