Bridge topics · Bridge types
Self-Anchored Suspension Bridge: How It Works and How It Is Built
A suspension bridge without ground anchorages: the main cables are tied to the deck ends and the deck carries their pull in compression. It suits soft ground and medium spans, at the price of building the deck first.
What a self-anchored suspension bridge is
In a normal suspension bridge the two main cables run over the towers and down into massive anchorages buried in rock or ground. The horizontal pull of the cables, which on a long span runs to tens of thousands of tonnes, is resisted by the earth. In a self-anchored suspension bridge the cables are tied to the ends of the deck instead. The deck resists the horizontal pull itself, as a long compression strut, and no external anchorage is needed.
The force flow is the same idea as a tied arch, turned upside down. The cable sags under the hanger loads and pulls inward on the deck ends. The deck pushes back. Vertical load reaches the towers through the cables and the end piers through the deck, and only vertical and modest horizontal forces reach the foundations.
Why engineers choose it
- Poor ground or no room for anchorages. On soft river or harbour deposits an earth anchorage can cost as much as a tower, and in a city there may be nowhere to put it. A self-anchored bridge only needs ordinary piers.
- Elevated approaches. Where the bridge sits high above the ground on a long viaduct, a gravity anchorage at deck level would be enormous. The self-anchored form puts the force into the deck, which is already there.
- The look of a suspension bridge on a medium span. Owners sometimes want the suspension silhouette for a landmark crossing of 150 m to 400 m, a range where an earth-anchored suspension bridge is rarely economic.
The catch: building it
A self-anchored suspension bridge has a construction problem that an earth-anchored one does not. The cable cannot hold anything until it is anchored, and it is anchored to the deck, so the deck has to exist before the cable can carry it. The usual sequence is therefore the reverse of normal suspension bridge erection:
- Build the towers and the end piers.
- Build the deck on temporary supports: falsework towers in the water or on land, or a temporary stay system. The deck is complete and continuous but not yet carried by the cables.
- Erect the main cables, anchor them to the deck ends, and install the hangers.
- Tension the hangers in stages. As the cables pick up load, the deck lifts off the temporary supports and the horizontal cable force builds up as compression in the deck.
- Remove the temporary supports and adjust hanger forces to the final geometry.
That falsework is the main cost and risk of the type. Over deep water, a navigation channel or soft ground, the temporary supports can cost a large fraction of the permanent structure, and the load transfer from falsework to cables needs careful monitoring because the deck goes from a multi-span beam on many supports to a suspended girder. The East Span of the San Francisco–Oakland Bay Bridge is the best known example: its steel box deck sections were set on two temporary steel truss bridges standing on driven piles, the single main cable was then spun as one continuous loop between the deck ends, and the deck was handed over to the cable by tensioning the suspenders group by group in three phases before the falsework was removed.
Design consequences
- The deck is a compression member. It must carry the full horizontal cable force plus bending, so it is designed against buckling as well as bending. Steel boxes, orthotropic decks and concrete boxes are all used; the compression is welcome in concrete and adds to the design load in steel.
- Cable sag and span. Sag ratios are similar to earth-anchored bridges, around 1/5 to 1/10 of the main span. A flatter cable means a larger horizontal force and therefore more compression in the deck.
- Span limit. Because the deck compression grows with span and the deck has to be erected on falsework, self-anchored suspension bridges stay in the medium-span range. The longest built so far is the 385 m main span of the San Francisco–Oakland Bay Bridge East Span.
- End details. The cable anchorage at the deck end carries the whole cable force into the girder and must also resist uplift, so the end span and end piers are often weighted or tied down.
Built examples
| Bridge | Country | Year | Main span | Notes |
|---|---|---|---|---|
| San Francisco–Oakland Bay Bridge, East Span | USA | 2013 | 385 m | single tower, single main cable looped under the deck ends |
| Pingsheng Bridge, Foshan | China | 2006 | 350 m | single tower |
| Yeongjong Grand Bridge, Incheon | South Korea | 2000 | 300 m | double deck: road above, AREX airport railway below; part of the 4.4 km crossing to Incheon Airport |
| Konohana Bridge, Osaka | Japan | 1990 | 300 m | a single main cable; the largest self-anchored suspension bridge when it opened |
The type is not new: Pittsburgh's Three Sisters bridges, built between 1924 and 1928, over the Allegheny River are early American examples.
Self-anchored or earth-anchored?
| Question | Self-anchored | Earth-anchored |
|---|---|---|
| Where does the cable pull go? | Into the deck as compression | Into gravity or rock anchorages |
| Foundations | Ordinary piers, good for weak ground | Large anchorages, need good ground or space |
| Erection | Deck first on falsework, then cable | Cable first, deck segments lifted from it |
| Economic main span | roughly 150 m to 400 m | roughly 400 m to beyond 1,000 m |
| Deck | Designed for large axial compression | Mainly bending and torsion |
A rough rule: if the span is long enough that falsework becomes impractical, or the ground can take an anchorage cheaply, the earth-anchored form wins. If the span is medium, the ground is soft and the owner wants a suspension bridge, the self-anchored form is worth studying alongside a cable-stayed option, which needs no falsework at all because it can be built as a free cantilever.
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Questions engineers ask
- What is the difference between a self-anchored and an earth-anchored suspension bridge?
- In an earth-anchored bridge the main cables are held by anchorages in the ground. In a self-anchored bridge they are tied to the ends of the deck, which carries the horizontal cable force as compression, so no ground anchorage is needed.
- Why does a self-anchored suspension bridge need falsework?
- The cable is anchored to the deck, so it cannot carry anything until the deck exists. The deck is therefore built first on temporary supports and transferred to the cables by tensioning the hangers.
- What is the longest self-anchored suspension bridge?
- The East Span of the San Francisco–Oakland Bay Bridge, opened in 2013, with a 385 m main span and a single tower.
- Is the Yeongjong Grand Bridge self-anchored?
- Yes. The double-deck bridge to Incheon Airport, completed in 2000, is a self-anchored suspension bridge with a 300 m main span, carrying road traffic on the upper deck and the AREX railway below.
- What span range suits a self-anchored suspension bridge?
- Medium spans, roughly 150 m to 400 m. Longer spans make the deck compression and the falsework too costly, and an earth-anchored or cable-stayed bridge usually wins.
Sources
- Self-anchored suspension bridge (Wikipedia)
- Yeongjong Bridge (Wikipedia)
- Konohana Bridge (Wikipedia)
- Eastern span replacement of the San Francisco–Oakland Bay Bridge (Wikipedia)
Updated 2026-10-25 · written by a practising bridge engineer