Chakzam Bridge

The Chagsam Bridge ( also Chakzam Bridge, Chushul Chakzam, Chusul Chakzam ) was a suspension bridge over the Yarlung Zangbo River at Qüxü ( Chushul ) southwest of Lhasa in Tibet.

It was built in 1430 by the Tibetan Buddhist philosopher, teacher, doctor, architect, smith and bridge builder Thangtong Gyelpo and was the largest and most important of, as was handed down, eight iron chain bridges built Thangtong Gyelpo over the Yarlung Tsangpo.

Location

The Chagsam Bridge was just above the mouth of the Lhasa Yarlung Zangbo River flowing in the Lhasa Hey, a few hundred meters below the modern road bridge and below the ferry, which also crossed the Yarlung Tsangpo up to their construction. She lay on the major caravan route from Lhasa to Gyantse and Shigatse, and on the way to the passes over the Himalayas to Nepal, Sikkim and Bhutan.

History

According to legend, the poorly dressed Thangtong Gyelpo was denied the crossing of the worried about their pay ferrymen, which so enraged him that he decided to build next to the ferry and a bridge above its southern pillar of a monastery. It was initially named after the place Chusul Chagsam, later just yet Chagsam or iron bridge. Although their use has always been free, some travelers feared the way across the bridge violently vibrating so much that they preferred the not -dangerous crossing of the raging river. Ippolito Desideri had already described in the 18th century that the chain bridges would be used only by people who were forced in their distress to the person familiar with dangerous situations Nain Singh had preferred the ferry on his first trip to Lhasa. The Pundit A.K. alias Kishen Singh has used them in 1878, according to his information, the sketch was made ​​. As Wadell in 1904 with the British Tibet campaign headed by Francis Younghusband came to the river, only the iron chains, as in the photo hung apparent, probably because of the Yarlung Tsangpo had trained a sidearm, which prevented further use. It was demolished in 1950 by the Chinese.

Description

Suspension bridge

The Chagsam Bridge was probably the first real suspension bridge, in which - unlike in a Spannbandbrücke - the path was not attached directly to the sagging chains and thus followed the curve, but with ropes of yak hair at a distance of about one meter as the two -bearing iron chains was attached that in the rope loops inserted, about a foot wide boards were held in a horizontal line. After the sketch of the way had no special railing, in the form of additional benefits associated with the hangers horizontal ropes, but was open on the side. The user therefore had to shimmy of each one of the vertical hanger to the next. The road was usually about 7.60 m above the water at high tide but still 4.6 m above the then rushing stream. The chains were attached to beams in the two brick pillars and continued into the bracing up to an attachment in the shore rocks or on the other side of the river bottom. A comparison of the photo with the sketch shows that this is only a schematic representation, the bridge piers were no towering towers, but stocky, a chorten same structures. On the south bank of the pillars stood on the rocky shore, the northern pillar stood on a small rise in the river bed which was usually dry beyond this pillar. Only at the end of the 19th century, the river seems to have north of this pillar formed a side who cut the bridge from the north shore.

Span

The span of the bridge was estimated by Wadell, who made the most accurate information about the bridge, at 150 yards = 137 m. The values ​​given in the sketch 300 steps provide contrast puzzle: the Pundits had largely constant step lengths of 80 cm trained, resulting in a span of 240 m and a distance between the shores of 800 m would result. In the results from the sketch slack in the chains of 1:11.5 requires such a span pillar heights of 20.9 m above the bridge deck and 25.5 m above the river water at high tide, but the photo is not in line to are bringing. Assuming that the step lengths have been cut in half on the shaky bridge, but to get though to one of the estimation of Wadell corresponding span, on the other hand to a width of the river bed, which is not to bring at least with the current realities in line. Anyway, had the bridge with a span of 137 m by far the largest wingspan of all former bridges.

Chain

The chains consisted of about 30 cm long and 5-8 cm wide chain links, which were forged of rectangular bars having a cross section of approximately 1.0 cm x 2.5 cm. Each chain should have had a weight of well over 550 kilograms. The chain links had therefore have been transported into short chain sections to the site and welded together individually or there, the question remains of how the chains were pulled and stretched over the river. Even after more than half a century, the chain links showed only slight signs of wear and virtually no corrosion.

After a chemical analysis of a chain piece from Bhutan, which probably also came from one of the built by Thangtong Gyalpo bridges, the iron contained only 0.2 % of impurities and had a carbon content of only 0.012 %. An investigation of the chain piece by the ETH Zurich revealed that the piece of iron mainly from α - iron crystals ( ferrite) was with portions containing iron carbide ( cementite ) and thus had a higher carbon content. At the weld was a less than 1/10 mm thick zone with significantly more severe iron crystals and with up to 2.6 % arsenic. Arsenical iron melts deeper than the other iron piece of the chain. Microscopic examination of the seam clearly showed that the surface was melted arsenic, which does not occur in normal fire welds of iron. It is not known how the thin arsenic layer was applied to the surfaces to be welded. Such a weld could be detected so far only in a Roman sword which comes from Germany, and probably in the first century AD. was forged in Damascus. The weld is based on a now unknown technology.