Chinese Rainbow Bridges - Structural Building Components .

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Chinese Rainbow BridgesWeiping SHENDr.-Ing.ProfessorDepartment of Civil EngineeringShanghai Jiao Tong UniversityShanghai 200030PR [email protected] Vitae:1946 born in Shanghai, China1969 received Bachelor degree from BeijingUniversity of Aeronautics, China1986 received Dr.-Ing from University ofStuttgart, Germany1990 – present Professor of Shanghai JiaoTong University, China1997 – 2004 Vice President of SJTUResearch interests: structural engineeringand computational mechanicsJie LIUMaster, Doctor CandidateAssociate ProfessorDepartment of ArchitectureShanghai Jiao Tong UniversityShanghai 200030PR [email protected] Vitae:1970 born in Chongqing, China1993 received Bachelor degree fromSouthwest Jiao Tong University, China2002 – present doctoral candidate ofTong Ji University, China2002 – present Associate Professor ofShanghai Jiao Tong University, ChinaResearch interests: history, theoryand design of architectureSummary“Qingming Festival on the River” is a famous painting from the Song dynasty. At the center of thispainting a wooden arch bridge is depicted, which is called “Bian-He Rainbow Bridge”. It was builtusing a very special ancient technique, “woven” of straight wooden logs. This type of bridge doesnot appear in any other part of the world, and has disappeared from China several hundred yearsago.900 years later in 1980’s several dozens of ancient timber arch bridges were discovered in themountain area of south Zhejiang and north Fujian Provinces. The structure of these bridges issuitable for large span and can cross river without any pier supports. These bridges are very similarto the Rainbow Bridge. In this paper the authors describe these bridges and their unique structures.Keywords: Rainbow Bridge, timber arch bridge, lounge bridge, timber arch lounge bridge, woventimber arch bridge, woven timber arch-beam bridge1. Introduction“Qingming Festival on the River” is a famous Chinese painting drawn by Zhang Zeduan in theSong dynasty. It depicts a festival scene 900 years ago in Bianjing (now Kaifeng, Henan Province),capital of the Song dynasty. The scroll painting is 25.5 cm high and 525 cm long, which illustratesboth sides of the River Bian-He and the street market during the Qingming festival. The painting isnow being kept in Forbidden City Museum. In the painting, an exquisite bridge is depicted at thecenter and is called the “Rainbow Bridge” (see Fig. 1). “Woven timber structure” was applied toconstruct the bridge. The details of the construction are clearly revealed by the delicate paintingskill and amazing craftsmanship.

According to the book “Dream in Eastern Capital” byMeng Yuanlao in the Song dynasty, there werethirteen (13) bridges spanning across River Bian-Heat that time. Three (3) of them were timber bridgeswithout pier supports, and crossed the river like arainbow. That might be the reason why they arenamed as “Rainbow Bridges”.In 1126, Bianjing was occupied by the troops of JinKingdom. Lin’an (now Hangzhou) became the newcapital of Southern Song dynasty. Between Jin andYuan dynasties this type of bridges graduallydisappeared from China. People thought that theFig. 1 The Bian-He Rainbow Bridgesecret of the construction of this type of bridge waslost. Many international researchers and scholars alsothought this unique construction which do not exist in the western society, would never have thechance to be seen in China.In 1999, NOVA of the United States organized a teamof engineers to China. Under the supervision ofProfessor Tang Huancheng, the American engineersand their Chinese colleagues re-built a rainbow bridgeusing the ancient techniques (see Fig. 2). This bridgeis located in Jinze Town, which is about 60 km westof Shanghai. The Americans team also produced a TVdocumentary “Secrets of Lost Empires - ChinaBridge” [1].In the early 1980’s, Chinese researchers found adozen of ancient timber arch bridges in the mountainareas of south Zhejiang and north Fujian Provinces.The structures of these bridges are quite similar toFig. 2 Rainbow bridge in Jinzhe Townthat of Rainbow Bridge. The result of these researchesis recorded in the book “Technology History of Chinese Ancient Bridges”, edited by Mao Yishengand was published in 1986 [2, 3]. There are eleven (11) bridges recorded in this book, including six(6) in Zhejiang, four (4) in Fujian and one (1) in Gansu Province.Since 1996 a research team on timber arch bridges led by thesecond author of this paper had gone to the mountain areas inthe Zhejian/Fujian province for eight consecutive years. Alltogether they inspected thirty-one (31) bridges in theZhejiang Province and nineteen (19) bridges of FujianProvince. The local colleagues also provided additionalinformation for another thirty-four (34) bridges in the FujianProvince [4]. It is believed that there are around one hundred(100) bridges of this type existing in that area (see Fig. 3).Fig. 3 Map of Zhejiang andFujian provinceIn this paper following terms will be often used.1) Bian-He Rainbow Bridge: the arch bridge depicted at thecenter of “Qingming Festival on the River”.2) Woven timber arch bridge: the special structure ofRainbow Bridge.3) Lounge bridge: the bridge with a lounge on its deck.There are about 300-400 bridges of this kind in theZhejiang and Fujian Provinces.4) Timber arch lounge bridge: timber arch bridge with lounge.It is a large scale bridge among the lounge bridges.

5) Woven timber arch-beam bridge: the special structure of timber arch lounge bridge.2. Example of Timber Arch Lounge Bridges2.1 The Oldest, Newest, and Longest BridgesThe oldest timber arch lounge bridge existed in last century was the Yeshuyang Bridge in theTaishun County, Zhejiang Province. It was built in 1454 and was demolished in 1965 due to theconstruction of a new road. It was 511 years old at that time [2].The bridge with the longest span was the Santan Bridge in the Taishun County, with a net span of42 m. It is a record in the Chinese ancient bridges. Santan Bridge is 5 m longer than the existingAnji stone arch bridge in the Hebei Province. Santan Bridge was destroyed by a flood in 1950 [2].The existing oldest bridge is the Rulong Bridge in Qinyuan County, Zhejiang Province, which wasbuilt in 1625. It is 28.2 m long, 5.1 m wide, and 19.5 m net span.There are two existing bridges with the longest spans, and they are located in the Shouning County,Fujian Province. Luanfeng Bridge is 47.6 m long, 4.9 m wide. Yangxitou Bridge was built in 1967and is 50.5 m long, 5.1 m wide. Both bridges have a net span of 37.6 m, and are similar to AnjiBridge. Yangxitou Bridge is the newest bridge, as there has no other bridge of this type constructedsince 1967. There were six (6) new and renovated bridges project during the 1950’s and 1960’s.2.2 Sister Bridges Over Dongxi StreamNear by the Sixi Town in Taishun County, Beijian and Xidong Bridges span over the DongxiStream. They are similar to each other and are called the sister bridges.Beijian Bridge was built in 1674, and is 51.9 m long, 5.4 m wide and 29 m net span [2] (see Fig. 4).Xidong Bridge was built in 1746, and is 41.7 m long, 4.9 m wide and 25.7 m net span [5,6] (seeFig. 5).Fig. 4 Beijian BridgeFig. 5 Xidong BridgeBoth bridges are the most beautiful ones among the lounge bridges. Their lounges have Chinesetraditional roofs covered with black tiles and curvy horn-like feature at the top pointing up into thesky. Both sides of the bridge are covered with overlapping red panel boards and serve as rainscreens. The setting around the Beijian Bridge is extraordinary. There are two streams merged onthe side of the bridge. Standing on one end of the bridge are two (2) thousand-year old camphortrees, with trunks over 2 m and shades over 10 m. From afar, there stand the Lion hill and theGeneral peak. This sets an extremely colorful and well coordinated natural scenery consisting ofthe ocean blue sky, milky cloud, mountains, pure streams, green leaves, black roof tiles, and redpanel boards.

2.3 Isolated Santiao BridgeSantiao Bridge in the Taishun County was built in 1843, and is 32.0 m long, 4.0 m wide, 21.3 mnet span, and 9.6 m elevated. During that time, it was situated in the main road between theZhejiang and Fujian Provinces. As time goes by, this area is scarcely populated. The nearest villageis half an hour of walking distance [5, 6] (see Fig. 6).Santiao Bridge is distant from the highway, andlocated at the bottom of valleys. Its architecturalform is simple, but the grayish side panels are ahistorical proof of its withstanding of a hundredyear of weathering. There is no spectacularcoloring on the bridge except some white, dullgray and black color from the roof structure andtiles. It looks pure, natural and graceful. The sizeof the bridge blends in with the surroundingsperfectly, it pierces through the water flowingthrough the streams, the boulders and cobblesstones scattering along the path. Walking alongsuch ancient lane or standing on the bridge is likeentering in a time tunnel, as one will see onlythings from hundred years ago. The vigorousFig. 6 Santiao Bridgevegetations give out another dimension of livingspirit in this so-isolated area. This harmony with the nature makes the writer feels the SantiaoBridge is the most beautiful one among the arch lounge bridges.The structure of Santiao Bridge is simple, clear and logical. In view of modern structuralmechanics it is almost perfect. It is a reflection of the superb craftsmanship in bridge building atthat time. The original site of the Santiao Bridge had other construction of bridges, which can bedated back to 7th-century and has important significance in history of ancient bridge engineering.3. Wonderful Structures of BridgesBridge engineers all know that structural members can withstand compression far more thanbending. Therefore, the loading capability and span of arch bridges are better than conventionalbridges. However, the difficulty is on how to effectively use straight logs to form the required arch!Nevertheless, the Chinese craftsmen already solved this challenge more than 900 years ago inbuilding the Bian-He Rainbow Bridge.3.1 Woven Timber Arch Bridge – Special Structure of Bian-He Rainbow BridgeFig. 7 Structure of Woven Timber Arch BridgeThe structure of Rainbow Bridge wascomposed of two kinds of timber frames;one 3-segment frame and the 4-segmentframe (see Fig. 7). The former had threecomponents equal in length, one centralround timber and two side timbers. Thelatter had two longer central timbers andtwo shorter side timbers. With theframes probably placed together, therewere five transverse spaces betweenframe joints and timbers. Five girderswere inserted into the spaces. They werebeneath the joints and sat above themiddle of timbers. The girders, jointsand timbers were then tied together with

bamboo ropes to form an arch structure.Bian-He Rainbow Bridge was composed of eleven (11) 4-segment frames and ten (10) 3-segmentframes. The bridge was around 18.5 m in length, 4.2 m in height and 9.6 m in width [2]. When thearch was loaded, abutments on either side of riverbanks absorbed the generated horizontal thrust.In view of structural mechanics the timbers behaved not in bending but in compression. So thisstructure was a pure arch. Computer simulation approved this conclusion.If we imagine the 3-segment frames and 4-segment frames are longitudinal fibers and the girdersare lateral fibers, the method to construct the bridge structures is just like the “woven” technology.Professor Yang Hongxun proposed to call this type of structure “woven timber arch bridge”.3.2 Woven Timber Arch-Beam Bridge – Special Structure of Timber Arch Lounge BridgesThe structure of timber arch lounge bridge is also composed of two kinds of frames, one 3-segmentand the other 5-segment. The 5-segment frame has three longer central and side timbers, and twoshorter corner timbers. When the frames are put together six transverse spaces are produced. Sixtransverse girders are used. This structure is quite similar to that of Rainbow Bridge. However,there are two differences between them. (1) The ends of timbers at joints are tenoned with girders,so ropes do not tie the girders, timbers and joints together. (2) There are two girders above thecentral timber of 3-segment frames, and will balanced with the central timber in the 5-segmentframes. This is a variation of a non-typical woven structure (see Fig. 8).The timber arch lounge bridges areusually built at the bottom of valleys.The tip of the arch is several meterslower than the road. The banks of theriver, the deck and the arch of the bridgeform two triangular spaces. The decktimbers, side timbers of the arch andother components are used to constructstrong trusses in the spaces. The side andcorner timbers are woven structure andloaded by compression. But the centraltimbers are applied by bending loads. Sothe whole structure behaves like a hybridof arch and beam. The authors proposeto call it “woven timber arch-beambridge”.Fig. 8 Structure of Woven Timber Arch-Beam Bridge4. Conclusions and Discussion4.1 Conclusions1) Bian-He Rainbow Bridge and the similar bridges existed in the Song dynasty and disappearedlater due to the fading of Bianjing. So there was no longer this type of bridge built in that area.2) Rainbow Bridge was a woven timber arch bridge. It was the most logical structure composedof straight timbers, and provided larger span and loading capability.3) There are around hundred timber arch lounge bridges in the Zhejiang and Fujian provinces ofChina. Their structures are similar to Rainbow Bridge.4) Timber arch lounge bridges are woven timber arch-beam bridges. They are suitable for longspan bridges.5) The arch lounge bridges in the Zhejiang and Fujian Provinces possess tremendous amount ofhistorical, cultural, technological, and economical significance and value. They are thetreasures of China and cultural heritages of the world.

4.2 Discussion4.2.1 Th