| Time-dependent properties are inherent characteristics of concrete which are different from other materials,and its shrinkage and creep have great influence on the concrete structures,especially on prestressed concrete bridges.The mechanism of-shrinkage and creep of concrete is complex and they are influenced by many factors.The prediction results of the existing prediction models for concrete under different conditions are far from each other.The time-dependent properties of high performance concrete are quite different from those of normal concrete,so it will cause certain deviations by using existing models to predict time-dependent behaviors of high performance concrete structures.In this paper,time-dependent properties of high performance concrete in the natural environment are studied in site tests,and the finite element model is established to analyze its influence on the bridge structures.Main works are as follows:(1)The impact of shrinkage and creep on concrete bridges is discussed and typical diseases and cases caused by them are listed.After that,research status and shortcomings of time-dependent properties of concrete are systematically summarized.(2)Characteristics,mechanism and influence factors of shrinkage and creep are reviewed in detail.At the same time,advantages and disadvantages of existing computational theories and methods of shrinkage and creep are compared.Then,the differences of existing predicting models of shrinkage and creep in formulas,considerations and application scope are analyzed.(3)The schemes of site tests are introduced and the results of strength,elastic modulus,shrinkage and creep characteristics of high performance concrete are analyzed.Then,they are compared with existing prediction models and the shortcomings of diverse prediction models for high performance concrete are pointed out.Finally,modified prediction models which are suitable for high performance concrete used in bridges are proposed.(4)According to the results of site tests,a finite element model is set up to analyze the performance of this bridge both in construction process and long term operation,using modified prediction models.At the same time,the results are compared with that of using Chinese design code and the differences in performance using these two prediction models are discussed.In that case,the impact of time-dependent properties of high performance concrete on bridges can be obtained and it can provide reference for future bridge construction. |
