Suspension Bridge

Long-span bridge hanging a roadway deck from vertical suspenders beneath parabolic main cables anchored at both ends.

Specifications & Metrics

type: Long-Span Bridge & Arch System
load mechanism: Deck live and dead loads transfer via vertical hangers into tension in parabolic main cables, compression in towers, and shear/tension in ground anchorages
governing relation: T_horizontal = w·L² / (8d) (horizontal cable tension for span L, sag d, and uniform deck load w per unit length)
classic configurations: Parallel-wire spun main cables with truss-stiffened or aerodynamic orthotropic box-girder decks
exemplars: 1915 Çanakkale Bridge (2,023 m main span), Akashi Kaikyō Bridge, Golden Gate Bridge, Brooklyn Bridge

Evolving from Thangtong Gyalpo's 15th-century Tibetan iron-chain bridges, James Finley's 1801 Jacob's Creek suspended-deck chain bridge, and John A. Roebling's in-situ wire-spinning method, suspension bridges achieve the longest clear spans of any human structure (2,023 meters on Turkey's 1915 Çanakkale Bridge).
Whereas a cable hanging under its own weight alone forms a hyperbolic cosine catenary curve, a suspension bridge cable supporting a much heavier, uniformly distributed horizontal roadway deck is pulled into a mathematical parabola.
After aeroelastic flutter from Von Kármán vortex shedding destroyed the plate-girder 1940 Tacoma Narrows Bridge, modern long-span suspension bridges adopt deep stiffening trusses or streamlined wind-tunnel-profiled closed steel box girders (introduced on the 1966 Severn Bridge).