These carry temporary trusses of timber or steel.
A load contains 36 trusses.
In the former the main supporting member or members may be an arch ring or arched ribs, suspension chains or ropes, or a pair of girders, beams or trusses.
From 1840, trusses, chiefly of timber but with wrought-iron tensionrods and cast-iron shoes, were adopted in America.
Intermediate piers support the trusses in the side spans.
