ANALYSIS OF CONCRETE CABLE STAYED BRIDGES FOR SECONDARY EFFECTS

Abstract

The inherent many-fold advantages associated with a modern day cable-stayed bridge are being realized increasingly by the design and practising engineers in the field of bridge engineering world over. Analytical studies and design of cable-stayed bridges for static and dynamic loads have been carried out by many investigators, but there is little information available about the studies related to the secondary effects of concrete, namely, shrinkage and creep in case of a concrete cable-stayed bridge where the girder/tower or both are made of concrete. In cable-stayed bridge, wheather precast segmental or cast-in-situ by the cantilever method, geometric control during construction is essential. The introduction of correction and adjustments during construction is difficult and expensive. To minimize these corrections, prior knowledge of the structural behaviour during every stage of erection and -after completion is needed. This requires an actual assessment of deformation and stresses in the structural elements at all stages of construction for the selected erection sequences. Keeping above in view, the time-dependent effects of creep and shrinkage of concrete on stresses and deflections in a segmentally erected 2-span concrete cable-stayed bridge have been investigated. To meet the purpose in case of a multi-stage construction like cable-stayed bridges, a two-dimensional stiffness matrix program has been developed to analyse these effects. Also, sag effects in cable-stays has been included in the program as a time independent geometric non-linear effect in the analysis. The method adopted is a step-by-step computer procedure in which the time is divided into intervals; the stresses and deformations at the end of each time interval are calculated in terms of the stress applied in the first interval and stress increments that occured in the preceding intervals. The loads that can be considered, are self weight, and any other superimposed sustained loads. Data related to material and geometric properties, construction and loading schedule are assumed to be available. In the present work, the vertical deflection of girder with time in the longitudinal direction, the variation of vertical deflection of typical girder nodes with time and variation of cable forces and member elasticity with time have been studied taking into account, sequence of construction, and time dependent effects of creep and shrinkage.