Analysis Of Shrinkage And Creep Effect For Long-Span Rigid Frame Bridges With High Piers

Shrinkage and creep are the inherent time-dependent characters of concrete which belongs to a viscoelastic material. It is important to accurately estimate and predicate the deformation and long-term deflection of long-span bridges with high piers which arise from the effect of shrinkage and creep for engineering design, quality control and construction process. Long-span continuous rigid frame bridges with high piers are sensitive to shrinkage and creep. Large error with respect to the predication of shrinkage and creep would lead to some difficulty of connection for segmental, cast-in-place concrete cantliver bridges and lead to deterioration of serviceability problems, aesthetics and eventually early reconstruction of the bridges. This thesis is initiated with the objective to analyze the effects of shrinkage and creep of this type bridges considerably accurately, to improve the predication precision of shrinkage of creep by mean of creating a more sophisticated numerical model, meanwhile to furnish some effective control data for construction and reliable analysis and comparision for long-term time-dependent deformation monitoring. Through the forgoing research work, the major findings are as follows: (1) Based on extensive newly investigation finding and much literature at home and abroad, and refered to the progress in concrete constituent mechanics analysis, the nature, mechanics performance under non-axial stress of shrinkage and creep are presented profoundly. Then the influence of activity admixture, reinforcement ratio of conventional bars, prestressed tendons and cylic load on shrinkage and creep are analyzed. Subsequently nonlinear creep damage model under limit state analysis is expatiated due to increasingly paying attention to nonlinear creep effect in civil engineering field. (2) In view of many new predication models abroad, which were deduced by large-scale experimental data and fitted by computerized optimization, this thesis presents explicit analysis to them. And compared with the model of new version JTG code (D62-2004), then their precision and applicability are represented respectively. (3) Analysis method of shrinkage and creep based on initial strain is mainly demonstrated, which considers the time-dependent effect of prestressed tendons and concrete comprehensively. On the basis of automatic triangular mesh generation scheme for beam element sections as a new method is presented in the thesis, the strain of every triangular area at sections which produced by shrinkage, creep, temperature gradient field, prestress relaxation etc. are calculated respectively, then the matrix of equivalent nodes load is deduced by means of internal force equalibrim in section, virtual work method and energy variation principle. Finally, time-dependent deformation is calculated through amending load column matrix and solving FEM equation, which avoids lower procedure efficience because of changing stiffness matrix continually in AEMM. (4) In view of great uncertainty factors in the effect of shrinkage and creep, stochastic finite element method (SFEM) is applied to structural analysis. It can calculate the coupled stochastic response of uncertainty factors through randomizing input variables representing the stastics stochastic factors. To reduce sampling number and assure simulation precision, Importance Sampling method and Latin Hypercube Sampling method are coupled with Neumann expansion SFEM respectively. (5) Based on above analysis methods, TDPA is programmed. Then it is used to time-dependent analysis of Bu Liu River bridge for ascertaining desirable construction parameters, mechanics characters and furnishing formwork elevation in segmental construction. Meanwhile sensitivity of main parameters is analyzed and some advantageous conclusions are gained for construction, quality control of Bu Liu River bridge.