The thirst for knowledge and the need to create have been the cornerstones of man’s progress over the last millennium. Without the desire to see what lies over the horizon and without questioning what we have been told by and learnt from previous generations we’d all still be living in caves.
Man’s ability to be innovative and attempt things that to previous generations would have seemed incredible, impossible or unbelievable has been the catalyst in creating the modern world. One of the most fascinating areas this has manifested itself is in bridge design and construction.
Travel, commerce, expansion, migration all have been influenced greatly by bridge design and construction. It has led to swathes of people being able to travel from one area to another and create new communities and sometimes whole countries. The ability to move across rivers, ravines and difficult terrain without any great problem has opened up trade routes and created dialogue amongst different communities and continents that would not previously have been possible.
Bridge design and construction can be broken down into three main types; simple, continuous and cantilever. These three basic design principles then cover all the different types of bridge design and construction including bean and girder, arch and truss.
Beam and girder bridges are usually made of metal or reinforced concrete. Beam and girder bridge design and construction has benefitted from the introduction of computer technology with many designs now owing a great deal to computer stress analysis. The design and construction of such buildings is now far more economical and predictable as a consequence.
The term ‘arch bridges’ includes constructions we know as suspension bridges. The bridge design and construction includes abutments at each end; the curve. All weight from both the bridge and its load is transferred into a horizontal thrust which is held by the abutments.
Truss bridges consist of connected pieces that carry load through tension or compression. They are one of the oldest types of modern bridge design and in terms of engineering are relatively straightforward to understand. Due to its efficient use of materials it was a popular form of bridge design and construction in the 18th and 19th centuries. Early American settlers constructed many truss bridges as they moved west across the continent because the wood was so abundant. It was easy to make the pieces needed for a truss bridge from wood and fit them together.
Erskine Bridge, Scotland – Beam and girder bridges are very common. They are usually the type used in road and rail construction because of their straightforward design, strength and longevity. The Erskine Bridge in Scotland is the A898 road that connects the M8 and A82. It enables 26,000 vehicles to cross the River Clyde every day.
The Pont du Gard, France – This aqueduct constructed by the Roman Empire is an example of arch bridge design and construction. The ability to make these types of construction stretched back to 1300 BC and so there are may examples to be found throughout the world. It is believed the Pont du Gard was constructed in the first century A.D. The fascinating thing about this bridge is that the stone was cut to such precise dimensions that there was no need for mortar as a fixing agent; completely unique to arch bridges. The Pont du Gard is listed as a World Heritage Site.
Sky Gate Bridge R, Japan – The truss bridge design and construction may be old and simple but that does not mean it is no longer used. Kansai International Airport lies on an artificial island in Osaka Bay. The island is connected to the mainland by the longest double-decked truss bridge in the world which carries both automobile and rail traffic.