Suspension    Domes

Hanging Bridge

Hanging bridges are a common sort of cheap and simple bridge in developing countries.

Typically they consist of a series of parallel cables strung across a ravine - with a walkway resting on the cables - like this:

Hanging bridge

Hanging bridge


There are two obvious problems with this bridge design.

  • It tends to act like a pendulum - and sway from side to side in the wind;

  • It is also free to oscillate in sinusoidal patterns in a vertical plane;

Since it is stabilised by no force other than gravity, its resistance to lateral force is particularly low.

These problems mean that hanging bridges are not terribly safe in adverse weather conditions - and don't scale up well.


The main way of stabilising such bridges in the past has been to turn them into suspension bridges - with overhead cables supporting the roadway beneath.

That is certainly one approach - and it generally works well. However it often requires the construction of expensive towers to be effective.

This essay is about the other possibility - stabilisation from the sides - and from below.

Stabilising hanging bridges

The suspension bridge illustrates a method by which bridges can be stabilised using a network of cables.

If there is sufficient room available below the bridge, there are other possibilites for stabilising such structures using cables - such as this one:

Stabilised hanging bridge

Stabilised hanging bridge

Here a vertical force is applied at each end of the bridge - and forces are applied by the cable network at about 20 degrees below the horizontal plane - resulting in a completly stable structure, invulnerable to both the lateral and vertical oscillations that plague traditional hanging bridges.

Pros and cons

The main advantage hanging bridges have over suspension bridges is that there's no need for costly towers - saving much of the time, effort and expense that goes into making such bridges.

However there are downsides:

  • There must be at least some space below the bridge for the cable network - such a network in a horizontal plane might guard against sideways oscillations - but would provide little defense against vertical sinusoidal waves.

  • To avoid undesirable slopes at either end, the bridge has to be pulled pretty taut. That means substantial ground anchors at each end - and some big fat cables.

The main ground anchors and the cables need to support not only the weight of the bridge - but they also need to resist the vertical component of the force applied by the cable network.

Compared to the cost of building towers, strong cables are likely to be relatively cheap - and larger ground anchors are also likely to be relatively inexpensive - but these additional expenses need to be factored into consideration of the design.

Availability of suitable conditions

Many bridges cross water. Space under them is often reserved for shipping - and the need for a cable network, or the reduce vertical distance under a hanging bridge may interfere with the passage of shipping under the bridge.

Not all rivers have tall banks. The stabilising cable network needs to lie below the hanging bridge. If erosion has not carved a deep enough groove in the landscape, then a hanging bridge may not be practical.


Where conditions allow their construction, hanging bridges seem like a great idea to me. I think such structures should be much more widely deployed.


The essay on lateral cables is related to this one.

Tim Tyler | Contact |