The Research On Closure Schemes And Long-term Deflection Of Multi-span Continuous Rigid Frame Bridges With High Spans

The continuous rigid frame bridge is built extensively due to its convenient construction as well as economy. In some long-span prestressed continuous rigid frame bridges, excessive deflections of main girders are often observed. These unacceptable deflections have detrimental influence on the serviceability and safety of the structures.The closure of multi-span continuous rigid frame bridges is one of important steps in the bridge construction. The selection of closure schemes determines the deformation and stress state of the bridge when construction is completed. In this paper, based on the situation of Jing River bridge, which is now under construction in Gansu Province, finite element method is applied to analyze and compare the internal forces, stresses and deformations of the bridge with 5 possible closure schemes. As a result, the most reasonable and engineering feasible closure scheme is obtained.Predicted deformations of continuous rigid frame bridges is not consistent with its measured deformations due to several factors. The great uncertainty in creep and shrinkage prediction in concrete constitutes the major difficulty. Other factors are the complex segmental construction procedure and the sensitivity of deformations to variations in the construction schedule, the uncertainty in estimating prestress loss and uncertainty in estimating model paremeters such as relative humidity. So, the factors such as prestress loss, concrete creep and shirinkage related to long term deflections of continuous rigid frame bridges are analyzed. And then, design and construction solutions of reducing deflections are proposed based on the previous results.To better understand and estimate short term and long term deflections for prestressed concrete box girder bridges, impact of differential shrinkage in box girder cross-section on deflection is analyzed. The results indicate that differential shrinkage has a great impact on long term deflections of continuous rigid frame bridge. The maximum downward deflection of Jing River Bridge caused by differiential shrinkage is-11.4 mm and the maximum downward deflection caused by uniform shrinkage is-39.4 mm 10 years after closure. The downward deflection considering uniform shrinkage can be 3.5 times as large as that considering differiential shrinkage. In addition, considering differential shrinkage in cross-section, downward deflections gradually become larger in the beginning and then become smaller. While, upward deflections gradually become smaller in the beginning and then become larger in the future.Finally, based on the construction plan and the construction schedule, finite element method was used to predict the internal forces and deformations of Jing River Bridge after closure.