Photo 6 : Chinese fir tree at Chengyang forest as the source of timber supply for construction of Dong wind and rain bridges and drum towers .
Engineering skills of the Dong tribe craftsmen
The components of traditional Dong wooden structures such as bridges , drum towers , drama stages and water-wheels fit together through a variety of tenons and mortises connections rather than nails or screws . Despite the precision that the design of the bridge demands , the builder embarks on each project guided solely by his mentally conceived plan . There are no construction drawings or plans . The Dong leading master , equivalent to chief engineer , also have the amazing ability to calculate complex mathematical computations mentally and thereafter translate them into symbols on a bamboo strips as their main measuring tool – in an esoteric script .
The art of such construction is passed down until now . The 1936 flood swept away three pavilions on the southern side of Yongji Bridge in Chengyang . Restoration began three years later with local craftsmen and completed two years later .
In 1984 , a second flood destroyed the two piers of Chengyang Bridge . The Wind and Rain Bridge underwent another large-scale restoration . The task was assigned in 1985 to the Dong tribe craftsmen headed by Yang Siyu and his father who shaped the timber to replace the ravaged bridge ’ s thousands of missing parts , mentally calculating the size of each raft , purlin and pillar and completed the restoration without any plan .
The art of Dong ’ s construction is well illustrated at the Chengyang village Dong museum . The varieties of timber tenon and mortise joints were crafted by skill craftsmen who shaped the timber with great precision using traditional cutting tools and measurement markings .
The markings on the timber for chiseling and fitting location are guided by the Dong ’ s method of special marking signs on bamboo strips since the Dong has no written language .
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