Suspension    Domes

Hybrid origins

I originally developed the idea of a suspension/cable-stayed hybrid bridge by modifying a suspension bridge.

This page preserves some of my workings.

While I'm an amateur bridge designer, I can't seem to shake my conviction that the professional designers have somehow got themselves stuck in a traditional rut - and are probably wasting millions of taxpayers dollars in the process.

More catenary cables

Here the idea is fairly simple: use additional caternary cables near the towers, to reduce the height the vertical suspension cables need to traverse.

More catenary cables

This idea keeps the catenary cable near to the body of the bridge.

That saves a considerable length of vertical suspension cable.

Some of the weight of the body of the bridge is supported by the cable that reaches the tower near its base. This weight no longer has to be supported by the upper part of the tower - which can consequently be made lighter and more cheaply.

The base of the tower is already likely to be very strong - and is probably already very well positioned to sustain this force.

The upper catenary cable no longer has to bear the entire weight of the bridge - since the regions near the towers have their weight borne directly by other cables.

Keeping the catenary cable close to the bridge's horizontal member results in greater stabilising forces against lateral perturbations.

This design reduces the extent to which the bridge acts like an aeolean harp - and minimises wind resistance.

The shorter cables have higher notes assocaited with them - and higher frequencies are more easily damped and are less likely to result in vibrations.

The lower catenary cable need only carry a small fraction of the weight of the main catenary cable - and can thus be made of lighter and cheaper stuff.

The cost of the additional catenary cables is likely to be greatly outweighed by the cost of all the vertical cables that are no longer needed, the cheaper towers, and thinner catenary cables that can be used.

The lower catenary cables should extend right across the entire length of the bridge. There is likely to be a section in the middle of the bridge where they run for some distance horizontal, level with the roadway. That is fine.

Application of the strategy described here can be expected to reduce both the weight and cost of large suspension bridges - allowing them to more easily attain larger spans.

Even more catenary cables

The above idea can be applied "recursively" - closer and closer to the towers.

Even more catenary cables

Some even earlier pictures follow:

More catenary cables

Even more catenary cables

Tim Tyler | Contact |