e-mosty March 2019 Long Span and Multiple Span Bridges - Page 45

MULTIPLE-SPAN SUSPENSION BRIDGES David Collings Figure 1: Taizhou Yangtze River Highway Bridge 3 This article provides a brief overview of multi-span suspension bridges for this issue of e-mosty magazine. Multi-span suspension bridges are a form steeped in history, as many of the early suspension bridges were multiple span structures 1 . It is also a re-emerging form with significant advantages over more conventional very long span bridges. A form of bridge which I am sure we will see more examples of in the near future. The traditional single span suspension bridge has been used for many of the world’s longest spans; this arrangement is ideal for a single obstacle of reasonable size and gives the stiffest suspension bridge form. Three span bridges with end spans of 20% to 40% of the main span can also be used for long spans; the shorter side spans do not adversely affect the overall behaviour of the bridge if kept within reasonable limits. The recent Ozmangazi Bridge across the Izmit Bay in Turkey 2 or the current longest span of 1991m of the Akashi-Kaikyo Bridge completed in 1998 are good examples of this bridge form. Other slightly longer conventional bridges such as Carnake at 2004m are being built. Longer spans such as the 2700m span Messina Crossing or bridges over fjords in Norway have been seriously proposed but not built, they tend to be very expensive. If the length of the side spans on these bridges is greater than 50% of the main span then the bridge becomes significantly more flexible and starts to behave as a multi-span structure. 1/2019