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为了分析长期使用中混凝土桥梁的结构表层干缩裂纹形成原因,以湿度扩散理论为基础,采用湿度变形耦合分析方法,研究了变湿度环境下的混凝土桥梁长期收缩变形、结构干缩自应力的分布规律及时变特征;通过经典试验对比分析,验证了所提出方法的可靠性;并通过模型尺寸效应的敏感性分析,进一步总结了混凝土结构的干缩自应力沿深度方向分布规律及随环境湿度变化而周期性变化规律。研究结果表明:混凝土收缩变形受到外界湿度的影响显著,特别是龄期100d后,混凝土试件的变形规律与环境湿度变化规律基本一致,随着环境湿度的升高,试件发生膨胀变形,而当环境湿度降低时,试件又发生收缩变形;环境湿度的周期变化对实桥结构整体变形及受力状态影响较小,约占收缩变形总量的12%,箱梁局部干缩应力随环境湿度的周期变化而变化,特别是干燥环境下混凝土内部压应力增大至-2.7MPa,同期混凝土外表面竖向压应力失去作用,并产生1.0 MPa拉应力,增大了腹板开裂风险;分析结果与实际桥梁腹板斜裂缝多为浅表裂纹现象相吻合;箱梁内部湿度变化幅度相对较低,箱梁腹板内缘混凝土自应力变化幅度小于外侧,这也揭示了实际桥梁箱梁腹板外表面裂缝数量明显多于内表面的形成机理。
In order to analyze the causes of the surface dry shrinkage cracks of concrete bridges in long-term use, based on the theory of humidity diffusion, the long-term shrinkage deformation of concrete bridges under variable humidity conditions and the distribution of self-stress of dry shrinkage are studied by using the method of humidity deformation coupling analysis Regularity and time-varying characteristics of the concrete structures. The reliability of the proposed method is verified through the comparison and analysis of classical tests. The distribution of self-stress of concrete structures in the depth direction and the variation with the humidity of the environment are further summarized through the sensitivity analysis of the model size effect The cyclical changes in the law. The results show that the shrinkage deformation of concrete is significantly affected by the external humidity. Especially after 100 days of age, the deformation of concrete specimens is basically consistent with that of environmental humidity. As the humidity of the environment increases, the specimen expands and deforms, When the ambient humidity decreases, the specimens shrink and deform again. The periodic variation of environmental humidity has little effect on the overall deformation and force state of the actual bridge structure, accounting for 12% of the total shrinkage and deformation. The local dry shrinkage stress of the box girder varies with the environment Humidity cycle changes, especially in dry environment, the internal compressive stress increases to -2.7MPa, the same time, the concrete surface vertical compressive stress and produce 1.0 MPa tensile stress, increasing the risk of web cracking; analysis The results are in good agreement with the fact that the oblique cracks in the webs of the bridge are mostly superficial cracks. The variation of humidity inside the box girder is relatively low, and the self-stress variation of the inner edge of the box girder web is less than that of the outer side. The number of cracks on the outer surface of the plate is obviously more than the formation mechanism of the inner surface.