What is a suspension bridge?


A suspension bridge is designed to carry road and rail traffic, often over great distances in a single span, to connect communities. The roadway is suspended from two long cables that straddle the towers. The weight of the bridge and the traffic is held by the cable being anchored at each end.

Early suspension bridges were made from rope and vines, some with wooden walkways, to transverse rivers and valleys. Over the last two centuries advances in the strength of steel and design innovations from leading engineers have created many bridges of over 1,000m in a single span.

The most iconic suspension bridge is the Golden Gate in San Francisco which was opened in 1937.

FAQ


What are the most iconic suspension bridges?

These famous suspension bridges set new standards: Thomas Telford’s Menai Straits Bridge to Anglesey (1826), the Brooklyn Bridge (1883) in New York, the Golden Gate Bridge (1927) in San Francisco, and the Severn Bridge (1966) connecting England and Wales.

How do you build a suspension bridge?

The towers are built first, sometimes on piers in the river bed.

The anchorages or abutments are formed at each end.

Then the cable is constructed by a wheel that takes wires back and forth from anchorage to anchorage over the towers. The thousands of individual wires are collected into bundles and compacted into two large, main cables.

Hangers are suspended vertically from the main cable.

Deck sections are then lifted up, connected to the hangers and welded together to form a continuous girder or roadway.

The road and rail surfaces are formed and the bridge opened for use.

What is the world's longest span suspension bridge?

The world record is currently the 1,991m-long Akashi-Kaikyo Bridge in Japan. In 2022, the Çanakkale 1915 Bridge across the Dardanelles in Turkey will set a new record of 2,023m.

The evolution of suspension bridges


In 1997, ten years after Bill Brown had been approached by the Societa Stretto di Messina to lead the Messina Bridge design project, he presented an evolution of suspension bridge building in five distinct stages to an engineering conference in Rome. He concluded with his plans for the crossing over the Messina Strait and named his presentation ‘The Road to Messina’.

Bill opened with a brief history of suspension bridge design, with the early nineteenth century schemes Menai Straits which used wrought-iron chains and linked eyebars. Then came Roebling’s iconic Brooklyn Bridge in New York and the riveted lattice-truss designs of vast American bridges. He presented the designs of the bridges he had played a major role in, from the new welded plate box decks of Severn and Bosphorus to the multi-box proposals for the Messina Bridge and Çanakkale Dardanelles.

© Stretto Di Messina

The future of suspension bridges


Bill Brown was constantly aware of the need for future advancements, declaring that: “Our objective must be to span distance more successfully than ever before, setting new standards in design and construction. It is our duty as designers and engineers to recognise, scrutinise and exceed past achievements.”

He set new standards particularly with his designs for the Severn Bridge and proposed Messina Crossing. He was undoubtedly ahead of his time with his innovative thinking. The Severn-type box girder deck has become a standard across the world and bridges with twin box decks, first conceived by Bill, are now being constructed.

He saw the probability of vast multi-spans across the Gibraltar Straits, ultra-long single spans in Turkey and the Far East. He recognised that with new, stronger steels there would be opportunity to span even greater distances. He planned bridges that combined of the benefits of suspension bridge design with those of cable-stayed and they have started to be realised.

We can only hypothesise on the future length of single spans. Messina, at 3,300m, is fully-designed and ready for the political will and financial strength to enable construction. Other ultra-long spans will surely follow and maybe 5,000m will be attainable in the future. Those engineers that follow in Bill’s footsteps, that match his technical ability and vision, will progress the profession and achieve greater distances distances in their bridge designs.