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.

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Fig.25 Building covered house

Fig.26 Ridges of the covered house

Fig.27 Sacrificial rites12)