COMPUTER SIMULATION OF BALANCED CANTILEVERCONSTUCTION OF CONCRETE BOX GIRDER BRIDGES

摘要

The balanced cantilever construction of prestressed concrete box-girder bridges has beenrecognized as one of the most efficient methods of bridge construction. This method has greatadvantages over other methods, especially in urban areas where traffic may be interrupted, or over deepvalleys or waterways where false work could be expensive and hazardous. Erecting segmental concretebridges with the balanced cantilever method may lead to longer spans with less cost and time ofconstruction. The continuity at bridge mid-span gives some advantages such as better serviceability, lessdeflection and better moment distribution along the bridge spans. Despite general design considerations,detailed calculations for long-term material deformation and deck deflection are necessary. Creep andshrinkage of concrete and relaxation of prestressing steel may lead to excess long-term deflection andmay cause redistributions in internal forces and stresses. As the construction stages go on, the staticallydeterminate structure changes to a statically indeterminate one, which should be considered in the designprocess. In this paper, a numerical analysis, using the commercially available ABAQUS software, isperformed to simulate the time history of erection procedure and the long-term behavior. A multi-spanbridge prototype is selected, on which time-dependent deformations of materials and changes in thestructural system of the bridge, after continuity of cables, are considered. Shell elements are used tomodel bottom and top slabs and webs of the box girder. The three-dimensional bridge model includesprestressing tendons with their exact geometries and properties. The time domain is divided into intervalsand a time-dependent static analysis is performed. Construction stages including initial prestressinglosses and long term deformations are considered. Comparison of the computer simulation withreachable experimental results is conducted and, good agreement between the present simulationtechnique and the available experimental results is observed. Deflections at the mid-span and longitudinalprofiles of the bridge during different construction stages and different ages after completion of structureare shown. Redistribution of moments and changes in stresses and strains are also illustrated.