BRIDGE ENGINEERING
37
Sidewalks may lie between the main systems or cantilever out on both sides. Stiffening Beams Stiffening beams distribute concentrated loads, reduce local deections, act as chords for the lateral system, and secure the aerodynamic stability of the structure. Spacing of the stiffening beams is controlled by the roadway width but is seldom less longitudinal compression equal to the horizontal component of the cable tension. Continuity Single-span suspension bridges are rare in engin- eering projects. They may occur in crossings of narrow gorges where the rock on both sides provides a reliable foundation for high-level cable anchorages. than the span. The overwhelming majority of suspension bridges have main cables draped over two towers. Stiffening beams may be either plate girders, box girders, or trusses. On major bridges, their Such bridges consist, thus, of a main span and two depth is at least of the main span. side spans. Preferred ratios of side span to main span are 1 : 4 to 1 : 2. Ratios of cable sag to main span are preferably in the range of 1 : 9 to 1 : 11, seldom Anchorages The main cables are anchored in massive concrete blocks or, where rock subgrade is capable of resisting cable tension, in concrete-ďŹ lled tunnels. Or the main cables are connected to the ends of the stiffening girders, which then are subjected to less than 1 : 12. If the side spans are short enough, the main cables may drop directly from the tower tops to the anchorages, in which case the deck is carried to the abutments on independent, single-span plate girders or trusses. Otherwise, the suspension system is extended over both side spans to the
FOR MORE DETAILS VISIT US ON WWW.IMTSINSTITUTE.COM OR CALL ON +91-9999554621