Chinese Bridges. Ronald G. Knapp

breaking of the beam as it exceeds its ability to bend. It is not surprising then, that practical experience led to the doubling or tripling of beams in order to increase strength, and a sequenced layering in order to extend the range.

      At the Chengyang Bridge in Ma’an village, Sanjiang, Guangxi, layers of protruding logs separated by transverse timbers provide cantilevered lifting for the covered bridge.

      Chinese bridge builders began in the fourth century CE to employ the cantilever principle—the layering of counterbalanced beams with each set of segments supporting additional beams that reach out towards a midpoint—in order to extend the clear span. This approach involved projecting out horizontal arms of wood, then later stone beams from weighted abutments of piled stone or masonry. Since a gap usually still remained, this opening between them was then spanned with a beam or set of beams. Single-span cantilevered wooden bridges, usually using logs, were frequently built to cross relatively narrow ravines in Yunnan and Sichuan provinces as well as in remote areas of Tibet. In Gansu, even relatively shallow streams were bridged by structures that soared using a cantilevered superstructure.

      Cantilevered stone beams are piled above the pier in order to lift the timber beams that support the corridor of the Dongguan (Eastern Pass) Bridge in Dongmei village, Dongguan township, Fujian.

      The 33-meter-long Yongqing (Eternal Celebration) Bridge, built in 1797, is lifted by a single cut-stone pier with both stone and timber cantilevering. Above the central corridor is a substantial second storey used as a temple. Sankui township, Taishun county, Zhejiang.

      Multiple spans of this type, each comprised of pairs of cantilevered supports, are found today in central and eastern China, especially in Fujian, Guangxi, Hunan, and Zhejiang provinces.

      Among the most notable cantilevered wooden bridges in China are the “wind-and-rain” bridges or fengyu qiao of the Dong minority group in southern China. Although the most notable feature of fengyu qiao is the series of colorful pavilions lined along their continuous galleried superstructure, the support beneath is also outstanding since it is usually comprised of sets of massive cantilevered logs. The Chengyang Bridge is another good example. With a length of 77.76 meters and four 17.3-meter-wide openings set upon five piers, it was constructed between 1912 and 1924 in the Sanjiang region of the Guangxi Zhuang Autonomous Region. Three cantilevered layers of fir logs—a series of projecting horizontal beams 7–8 meters in length—are laid longitudinally across the top of each of the five stone piers. Between the four levels of cantilevered logs, which are held firm by tenoned timbers, are thin spacer logs that together stabilize the support and also provide some degree of flexibility. In this region, as elsewhere in southern China, when rebuilding of dilapidated cantilevered structures took place, the length of spans could be maintained by cantilevering more logs of shorter length than were originally used. The Lujiang Bridge in Hunan province, first built in the middle of the thirteenth century and rebuilt many times, at one point had ten layers of cantilevered logs to enable its span.

      Activities along as well as in the water beneath an arch bridge crossing the Si River in Shandong province, are exhibited in this rubbing from an engraved brick of the Eastern Han period (CE 25–220).

      Arch Bridges

      Arches in many shapes and configurations, employing both stone and wood as materials, epitomize the superlative achievements of Chinese bridge building. Stone arch bridges are ubiquitous in China, but arches constructed of timbers, which are sometimes called “rainbow bridges,” are much more limited in their extent. Varying widely in form and in clear span, many arch bridges are merely functional and rather primitive, while others display not only astonishing design skills and techniques of construction but also express exquisite beauty. It is not known definitively when the first stone or timber arch bridges emerged in China but both forms developed independently of those in the West. Since arches are stronger than planks, whether the material is stone or wood, the evolution of arch forms made for the possibility of greater spans and heights. Arches are said to be in compression, pushing outward rather than transferring their weight downward as with planks, and as a result require substantial foundations.

      Carved on the surface of a baked brick, this image depicts a horse-drawn carriage and a porter with a carrying pole crossing an arch bridge, which is reinforced with vertical supports beneath.

      This tableaux of county scenes in Huizhou, found today in a temple near the Bei’an Bridge in southern Anhui province, includes a steep single-arch bridge with a pavilion atop it.

      Although the scholars drinking in the wooded countryside are the main theme of Shitao’s early eighteenth-century Drunk in Autumn Woods, this virtuosic painting incorporates elements that could be found in a small park or garden, including a fine bridge, pavilions, and paths. ©The Metropolitan Museum of Art, New York.

      Shown in this painting by a European is a somewhat fanciful bridge with billowing ornamentation above it that was clearly built so that large vessels, shown in the foreground, could pass easily beneath its soaring arch.

      The Wanxian Bridge in Sichuan was photographed at the end of the nineteenth century by Isabella L. Bird, who stated: ”I have never seen so beautiful a bridge as the lofty, single stone arch, with a house at the highest part, which spans the river bed, and which seems to spring out of the rock without any visible abutments” (1900: 47)

      The Dongshuang (East Paired) Bridge, perhaps built during the Song dynasty in Shaoxing, Zhejiang, is considered one of the finest single-arch extant bridges. Its mate, the Xishuang (West Paired) Bridge, no longer exists.

      Stone Arch Bridges

      In southern China, single- and multiple-arch bridges often rise precipitously above narrow canals, while others lay close to the water, with a continuous pattern of repeating arches from bank to bank, a form that is also common in northern China. Among the earliest representations of stone arch bridges are those of the Eastern Han period (CE 25–220) inscribed on fired brick tiles that have been excavated from underground tombs—themselves often constructed with arch ceilings—throughout northern China. In Henan province, a brick reveals an unadorned curved span being crossed by pedestrians, a mounted horse, and a carriage drawn by four horses with boats and fish beneath. The steep approaches are apparent, reinforced by the presence of muscular men towing the carriage up the deck, with others controlling the carriage as it descends.

      The arch is a shape that carries its load outward as a result of compression that produces horizontal outward thrusts towards the bridge’s abutments. In spite of the durability of stone, moreover, Chinese stone arch bridges reveal a remarkable plasticity, a “resisting by yielding,” according to Chinese bridge builders. Throughout the Jiangnan region, where sandy soil made it difficult to sink solid foundations, bridge builders learned to make use of vertical sheer walls of stone slabs to receive those forces that might tend to deform the arch. The Chinese rarely used mortar as a bond between stones. Rather, stones were generally carefully shaped and sometimes mortised into each other or joined together by overlapping iron cramps. As a result of these techniques and the ensuing elasticity of the stone shell, stone arch bridges