Stochastic Analysis About Long-Term Deflection Of Long-Span Prestressed Concrete Continuous Rigid Frame Bridge

The continuous and excessive mid-span deflection has become one of the most severe defects of prestressed concrete continuous rigid frame bridges. It significantly influences the riding comfort and bridge safety.On one hand, the concrete’s creep and shrinkage may cause the redistribution of internal force and the enlargement of structural deformation of rigid fame bridges. They are easily impacted by lots of random factors, so the creep and shrinkage effect shows a remarkable randomness. On the other hand, the prestressing system in rigid frame bridges plays an important role in resisting the bridges’deflection. It can be affected as well by uncertain factors in environment, construction and steel strand’s corrosion, so its effects are not definitive. However, the randomness of parameters is not taken into account in the traditional determinist analysis for bridge design. Therefore, a significant difference between the design objective and the physical truth may be created in the realm of concrete creep and shrinkage effect as well as the effective prestress. These may become the main reasons causing the excessive mid-span deflection of long-span prestressed concrete continuous rigid frame bridges.Based on the preceding reasons and taking an existing bridge as engineering example, a stochastic analysis was carried out in the thesis about the long-term deflection of long-span prestressed concrete continuous rigid frame bridges, with consideration of several main random factors probably causing the bridges’ long-term deformation. The following studies are mainly involved:(1) In order to provide theoretical basics for this thesis, literature reviews and theory introduction were developed on the following subjects:the deflection causes for long-span prestressed concrete continuous rigid frame bridges; the analytical theories about the concrete creep and shrinkage as well as the chloride corrosion of prestressing steel strand; the stochastic methods for the structural long-term deformation analysis.(2) Considering the randomness of affecting variables, a stochastic analysis about the given bridge’s long-term mid-span deflection was conducted in this thesis. The analysis was focused respectively on two aspects of concrete creep and shrinkage effect as well as the chloride corrosion effect of prestressing steel strand. A technique combining the Response Surface Method with Monte Carlo sampling was used in the process. The statistic characteristics and the probabilistic prediction of deflection were achieved. The result indicates that the bridge mid-span defelction has an apparent randomness caused by the two preceding effects, so the stochastic analysis of long-term defelction is highly recommended in bridge design.(3) A discussion was developed about how the stochastic variables, as the control stress for prestressing and the corrosion rate in different deterioration levels, might influence the long-term mid-span deflection. Comparing the probalistically predicted deflection with the measured deflection of the given bridge, a conclusion can be drawn that the randomness of these two preceding variables may both cause the bridge’s over deflection.