e-mosty March 2019 Long Span and Multiple Span Bridges - Page 48

Over the years many ways of stiffening a multi span suspension bridge have been tried with varying degrees of success. particularly if the cables are clamped together where they cross. If additional cables are used to restrain the tower tops a similar appearance is generated (Figure 8d), the Cuzbac Bridge in Figure 2 has this form (although the cable arrangements could be as shown in Figure 8c). A number of these methods are shown in Figure 8. The first group of ways is to stiffen the cable system. The range of modern cable span to sag ratio is from 7:1 to 14:1. Reducing the cable sag (or increasing the span-sag ratio) increases the cable stiffness. To restrain the tower these inclined cables need sufficient strength to carry the live loads and stiffness to restrain the towers. Considering further the cable geometry, but exploring the use of twin cable systems: The use of twin separated cables with different sags helps stiffen the bridge (Figure 8b). If additional cables are used tying the tops of the towers together (Figure 8e) a more efficient method results. The method of tying the tower tops has been used on a number of multi-span bridges in France such as the Loire Bridge in Figure 3. If pairs of cables are used, each supporting half of the bridge span (Figure 8c), a stiffer layout results, Figure 8: Methods of stiffening cables 1/2019 1