PARAMETRIC STUDY FOR LMV SUSPENSION BRIDGES

Abstract

In the hilly regions of India, which have a very significant area, cable bridges are commonly built to span deep gorges over fast flowing streams to maintain pathways. With fast development of the hill regions and increasing road traffic, many more cable bridges need to be built utilizing latest materials and technologies, particularly to meet the requirements of increasing spans as well as traffic.The suspension bridge is the most common type of bridge constructed in the hill regions in India. Four light motor vehicle (LMV) suspension bridges of 198 m, 252 m, 300 m and 402 m span have been taken up for parametric study in this dissertation. The study has been carried out to see the variation in the forces with span in main cables, wind cables, towers, reverse cables and also the variation of moments in the tower. Variation of maximum vertical displacement of the deck with span is also studied. The parameters which are varied for this study are span, height of tower, sag of main cable, sag of reverse cable and sag of wind cable. In the study it was found that forces in the main cable, reverse cable, wind cable and tower (axial) vary linearly with span. Also the main force in towers is the axial force, not the moment. The bridge is not so sensitive to earthquake forces primarily due to its structural arrangement. It is also interesting to see that in a light motor vehicle suspension bridge the governing live load for various cables (main, reverse, wind), towers, abutments, stiffening girder and cable anchor blocks is not the vehicular load but the pedestrian loading. Detailed design for a typical span of 402 m has been carried out to illustrate the analysis and design procedure adopted to arrive at a suitable design.