The Large Box Girder Linear Observation And Control Of Prefabricated And System Conversion

Combined with Key Technology Research of Hangzhou Bay Trans-ocean Bridge(2003-319-h01-010), one of the Communication Ministry Technology Items, the dissertation studies the measure and control of linear shape for 70m box girder in precast stage and system transformation stage from simple-supported into continuous structure. It presents 70m box girder's integral prefabrication, move and marine erection, which can provide useful experiences for large box girder construction.Double-prestressing method is a distinguished creation in Hangzhou Bay trans-ocean Bridge construction. The research shows that double-prestressing method, an effective measure to control concrete cracks in its early period proved by practice, does not influence long-term alignment of box girder.The analysis of box girder's alignment during system transformation stage indicates that 70m box girder has great stiffness, so the change of closure sequence of prestressed tendon has little effect on alignment. In addition, the age difference between the precast concrete and wet-joint concrete's influence on alignment cannot be ignored, and it is rational to undertake system transformation around 80th days.The parameter analysis shows that prestressed pipeline frictional coefficient, the deviation factor, modulus of elasticity, temperature difference, concrete shrinkage and creep are key factors to box girder's alignment. Five concrete shrinkage and creep theories are adopted to analyze the continuous box girder: deflection resulted from the method presented by standard JTG D62-2004 is the maximum while that from the method presented by standard JTG 023-85 is the minimum; the results calculated by modified ageing method, numerical calculation according to given time curve, ageing theory are medium.At last, it tests and records on-site data in the whole construction process, and then compares the records with the results from theory analysis.