NUMERICAL STUDIES ON CABLE STAYED AND EXTRADOSED BRIDGE

Abstract

Cable stayed and extradosed bridge are similar structures which utilize the cables to support the deck. However, extradosed bridge can be defined as the subset of cable stayed bridge that employs relatively short towers and stiff girder system and at relatively flat horizontal angles of the cable with the deck. Both the types of bridges are used for spans of above 100 m. However, less study is available in literature to show the quantitative difference in their behavior with varying span. Hence, an attempt has been made in this thesis to bring out the difference in the behavior of cable stayed and extradosed bridge due to variation in parameter related to cables, pylon and deck through numerical studies. Determination of the cable tension is a very crucial step in designing the cable stayed and extradosed bridge. Since the continuous beam method does not consider the effect of stiffness of the pylon, the tension obtained from it may not produce desired bridge profile and bending moment. So, a modified approach is proposed in this work. The modification reduces the deflection of the bridge and bending moment in deck significantly. Also, the force equilibrium method has been implemented using the SAP 2000 for finding the cable tension. Since the main difference between the cable stayed and extradosed bridge is pylon height. A parametric study is performed to determine its influence by varying the height. Different bridge models of cable stayed and extradosed bridge are made for spans of 100 m, 200 m, 300 and 400 m. The difference in the load sharing of the cables is studied. Since cable stayed and extradosed bridge are large structures, so relative significance of beam column effect and large displacement is studied. Also, comparison between both types of bridge is done based on the variation of sectional forces with the increasing span.