STUDY OF EFFECT OF HYDRODYNAMIC PRESSURE IN BRIDGE SUBSTRUCTURES

Abstract

This thesis concerns with the study of hydrodynamic effect and its influence on response of bridge substructure. It is not yet known, to what extent, hydrodynamic effect is important for bridge substructure having tall or short piers. The hydrodynamic effect is dependent upon depth of submergence, shape and size of piers, flexibility of pier and character of ground motion. The codal methods usually adopt a simplified approach of cylinder analogy to consider piers having non circular shapes. In this study the main objective of investigation has been to determine the contribution of hydrodynamic effect in relation to seismic effect due to inertia of structure. In this study two aqueducts having wall type piers and heights equal to 64.54 m and 5.3 m respectively are considered and one bridge having circular pier and height equal to 107.50 m is also considered. The dynamic response of bridge/aqueduct are computed using response spectrum method. The site response spectra are used for each structure. The hydrodynamic effect is included by considering added mass of water on the basis of cylinder analogy. The seismic analysis is carried out with and without added mass of water for each structure. The effect of added mass of water is studied on time period, bending moment and shear force in each structure. The comparison of total hydrodynamic forces computed by IS:1893 and SEHB (Japan) for each structure is also made. It has been found on the basis of study that time period is elongated due to added mass of water. The elongation depends on shape and size of pier and the height of structure. The bending moment and shear force at the base of pier is also increased due to hydrodynamic effect, the increase is again dependent- upon, the shape, size and height of pier. The hydrodynamic force computed by SEHB (Japan) for column type of piers is more as compared to IS:1893, while for wall type piers, IS:1893 gives larger value of hydrodynamic force as compared to SEHB (Japan) .