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History of Bridges

In the Beginning……... Natural Bridges Bridges

The first man made bridges: Simple beam bridge Logs formed the beams Bridges

BRIDGES OF SUBSTANTIAL LENGTH CAN BE BUILT USING A SERIES OF SIMPLE BEAM SPANS

THE LONGEST BRIDGE SYSTEM IN THE WORLD IS THE 18 MILE LONG CHESAPEAKE BAY BRIDGE - TUNNEL. MOST OF THIS SPAN CONSISTS OF SIMPLE BEAMS

VIRGINIA BEACH CAPE CHARLES

USS Harry S. Truman Builders’ Sea Trials June 1998

When all a society has to build with is stone and wood, the individual span lengths of a simple beam bridge are very short. New technology was needed to: Span greater distances Withstand greater loads Withstand the effects of weathering SOLUTION: THE ARCH Bridges

With arches, everything is in compression all the time

As with simple beam bridges, long spans can be realized by using multiple arches Bridges

Once materials were available to engineers which could be loaded in tension, a new type of arch bridge appeared: This was the suspended deck arch bridge.

The need to span increased distances continued to pressure bridge designers. With the new material of steel available, with its superior performance in tension, new designs made bridges longer and stronger. Steel made the TRUSS BRIDGE possible. Bridges

Still, longer spans were required. As technology developed, and materials became available, a new variation on an old design was possible. This dramatically increased the total span length. This is the SUSPENSION BRIDGE

The cables of a suspension bridge are not fixed to the tops of the towers. Rather, as this photo shows, they are free to move as the bridge moves. Bridges

2 Km

The January 17, 1995 Kobe earthquake had its epicenter right between the two towers of the Akashi Straits Bridge. The original planned length was 1990 meters for the main span, but the seismic event moved the towers apart by almost a meter. Since construction of the deck had not yet begun, the change was easily accommodated in the slightly altered final design. The towers of the bridge contain tuned mass dampers in order to diminish the vibrations in the structure during earthquakes.

The most recent development in bridge design does not make any dramatic increases in span length. Rather, it allows mid-sized bridges to built with less material, therefore making bridges more economical to build and maintain. These are the CABLE - STAYED bridges Bridges

What does the immediate future hold? As new strong, lightweight synthetic materials become more common, ever more impressive bridges will be built. The current “next step” is to bridge the Straits of Gibraltar. Bridges