The segmental arch bridge

A conceptual breakthrough occured when a Chinese engineer was the first torealize that an arch did no have to be a semi-circle. A bridge could be built which was based not on the traditional semi-circle arch but on what is known as a segmental arch. The way to envisage this is to imagine a gigantic circle embedded in the ground, of which only the tip shows above ground level. This tip is a segment of a circle, and the arch it forms is a segmental arch. Such an arch forms the central arch of the bridge in the picture. Bridges built in this way take less material and are stronger than ones built as semi-circlar arches.

This advance took place in China in the seventh century AD. It was the concept of a genius, Li Ch'un, the founder of an entire school of constructional engineering whose influence lasted for many centuries. We are fortunate in that his first great bridge, built in 610, survives intact and is still very much in use today. Called the Great Stone Bridge, it spans the Chiao Shui river near Chao-hsien, at the foot of the Shansi Mountains on the edge of the North China Plain. It was featured on postage stamp in 1961 and is one of the achievements of early Chinese engineers of which the modern Chinese have most knowledge, and of which they feel most proud. Many legends have attached themselves to the bridge over the centuries, and about the sixteenth century a poet spoke of it as 'looking like a moon rising above the clouds, or a long rainbow hanging on a mountain waterfall'.