PROPOSED PROCEDURE FOR ESTIMATING MAXIMUM NORMAL FORCE IN CABLE-STAYED BRIDGE

Abstract

Most cable stayed bridges are very slender with high compressive forces in both

_ girder and towers. The cable-stayed bridge is a statically indeterminate structure with a large degree of redundancy. The bridge deck around the pylon is subjected to compressive axial forces; these compressive axial forces reduce the capacity of the bridge deck. Therefore, the critical buckling load of the deck decreases. So the stability analysis of cable stayed bridge warrants careful investigation.

In this work, a proposed method for estimating the maximum normal force in deck of cable-stayed bridges is derived and presented to use it in the preliminary design. The finite element program, STRAND 7, was utilized and compared with proposed method.

The structural behavior of a bridge deck becomes nonlinear because of the axial forces, large deflection, and nonlinear behavior of cables and the large deformation of the pylons as well as their interactions but in the preliminary design we need to simple and fast method to estimate the maximum normal force in deck without need to make finite element model so this proposed method based on linear static behavior of cable-stayed bridges.

In this thesis the overall buckling of this type of bridge will be studied. Because the cables, the girder, and the tower are all interconnected to each other, the whole structure will be treated as one entirety. Local stability will not be considered. Tang's equation will be used to calculate the buckling load, the girder is like a continuous beam elastically supported at the points of cable attachments and supported on rollers at the towers.

Two and three dimensional models are used here and compared the results from proposed equation with the finite element model results. The finite element model for cable -stayed bridges was established using the finite frame element for girder and towers and finite truss element for cables.