During the nineteenth century there was a shift in materials used for construction; iron and concrete gained significant popularity. With these heavier materials and increased desire for functionalism, architects sought new advances to technology to support weight. The bridges of the time are the greatest remnants of their success.
The iron suspension bridge was introduced in the 1800s and the biggest problem designers faced was creating stable structures that would be able to resist various wind speeds. There were many failures along the way but two bridges stand out from the time period that would leave their mark and stand the test of time – the Brooklyn Bridge, New York and the Forth Bridge, Scotland.
Brooklyn Bridge, John A. Roebling, 1883
Bringing the industrial world into the architectural world resulted in growth of a new type of city; a city born out of successful industrial growth. Industry and its marvels are reflected in everywhere. These bridges are the prime lasting monument of all these innovations. The challenge of building a bridge is it must not collapse, obviously, and it must span over bodies distant bodies of land. The key is to balance the weight throughout the bridge.
It was resolved in a very interesting way – John A. Roebling was a famous iron suspension bridge designer in his time, but the crown jewel of his career was his design for the Brooklyn Bridge in 1883. At it’s creation, it became the world’s largest bridge and was also the first suspension bridge to use steel wires as main cables. There are two massive piers that would act as the columns would in a cathedral and then thin looking suspension wires would deflect the weight in waves. The middle span of the bridge does not collapse because it does not carry the entire weight of the structure. The Brooklyn Bridge ties two generations of building materials – bridge is made of heavy stone, the piers are pointed arches and yet are combined with all the 1800s technological advancements, such as the steel cables. This is not to say that engineers looked upon this as a piece of architecture – its a modern idea along with railways and parkways – a narrow look at architecture would say this is simply is functionalist structure. They had an idea of what a bridge was suppose to look like and it would function as just that – a bridge.
Forth Bridge, Scotland,Sir John Fowler and Sir Benjamin Baker, 1890
The Forth Bridge, also known as the “Forth Rail Bridge”, was made completely of steel. This huge cantilever truss bridge over the Firth of Forth in Scotland surpassed the Brooklyn Suspension bridge with a distance of 521 meters and became the longest suspended bridge in the world, circa 1890.Three pillars connected by two sets of arched tresses support the weight of 55,000 tons of steel, 18,122 m³ of granite and over eight million rivets, all while spanning over 1.5 miles. This design was brought forward by Sir John Fowler and Sir Benjamin Baker.Deflecting the weight in waves between the heaviest points to the lightest points, the cantilever was the ultimate solution…
Although the cantilever bridge was previously done, it was never executed on such scale as Forth Bridge. The work done was without precedent. It included calculations for incidence of erection stresses, provisions made for reducing future maintenance costs, calculations for wind pressures and the effect of temperature stresses on the structure, etc.
These things could not have be done with other materials. In the 1890s no one had seen anything like it – some hated it saying it broke away from traditional architecture and so it was in a sense modern for it’s time. Ideas like how forces traveled through space and physics were further developed. Engineers and architects a could draw formulas to calculate stress, and this was revolutionary.
- A cantilever is a beam supported on only one end. The beam carries the load to the support where it is resisted by moment and shear stress. Cantilever construction allows for overhanging structures without external bracing. Cantilevers can also be constructed with trusses or slabs.
- A cantilever bridge is a bridge built using cantilevers, structures that project horizontally into space, supported on only one end.
Good composition is like a suspension bridge – each line adds strength and takes none away.