高强混凝土早龄期拉伸与压缩徐变特性及其结构非线性徐变应力计算方法研究

High strength concrete is widely used in large span bridge structures. The early crack of high strength concrete for bridge is very common, which can affect the structural performance seriously. The characteristic of early age tensile creep and compressive creep and theories of calculation method for creep stress are key factors for the crack prediction and prevention. Currently, the study on concrete creep focuses on matured concrete, while for early age concrete further study is still needed. Based on the current studies and consider the feature of high strength concrete, experiment would be carried to research on the early age tensile creep and compressive creep. The factors such as strength of concrete, load age, ratio of volume to superficial area, curing temperature, content of fly ash and reinforcement ratio are concerned in the experimental study. The applicability of current prediction models is evaluated and the prediction model for early age concrete creep is proposed. Based on solidification theory, the calculation method for nonlinear creep stress with early age tensile creep and compressive creep considered is developed. Based on the prediction model and calculation method, simulation analysis and verification of thermal stress of a large span PC box girder bridge during construction are conducted. The research achievements of the project would be of great practical and theoretic significance to the design and construction of high strength concrete structures.

高强混凝土广泛应用于大跨度桥梁工程，然而在其养护期间普遍存在开裂现象并严重影响结构性能。高强混凝土早龄期拉伸、压缩徐变特性及其结构徐变应力计算方法是对其早期裂缝进行有效预测并控制的关键。现有的徐变研究侧重于成熟混凝土，早龄期徐变相关的科学研究有待进一步深入。项目结合已有的研究成果，针对高强混凝土特点，设计正交试验对影响其早龄期拉伸、压缩徐变的重要参数如强度等级、加载龄期、体表比、养护温度、粉煤灰掺量和配筋率等进行系统研究。据试验结果对现有徐变预测模型的适用性予以评估，并建立桥梁高强混凝土早龄期拉伸、压缩徐变预测模型。基于固化徐变理论，提出早龄期混凝土结构同时考虑受拉和受压应力松弛特性的非线性徐变应力理论计算方法。最后，采用所提预测模型和分析方法，对已完成现场实测的大跨预应力混凝土箱梁桥养护期间水化热温致应力进行仿真分析和验证。项目研究成果可为高强混凝土结构设计及相关规范的完善提供理论依据。

高强混凝土广泛应用于高层结构和大跨度桥梁工程，然而在其养护期间普遍存在开裂现象并严重影响结构性能。高强混凝土早龄期拉伸、压缩徐变特性及其结构徐变应力计算方法是对其早期裂缝进行有效预测并控制的关键。现有的徐变研究侧重于成熟混凝土，早龄期徐变相关的科学研究有待进一步深入。项目结合已有的研究成果，针对高强混凝土特点，较系统的研究了高强混凝土早龄期抗压强度、弹性模量等物理力学性能发展规律；设计正交试验对影响其早龄期拉伸、压缩徐变的重要参数如强度等级、加载龄期、体表比、养护温度、配筋率和应力水平等进行系统研究。据试验结果对现有徐变预测模型的适用性予以评估，并建立桥梁高强混凝土早龄期拉伸、压缩徐变预测模型，确定了非线性徐临界变应力比。基于固化徐变理论，提出早龄期混凝土结构同时考虑受拉和受压应力松弛特性的非线性徐变应力理论计算方法。最后，采用所提预测模型和分析方法，对已完成现场实测的920m主跨斜拉桥大体积承台混凝土养护期间水化热温致应力进行仿真分析和验证。项目研究成果可为高强混凝土结构设计及相关规范的完善提供理论依据。