摘要
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。
To analyze the forming reasons of cracking led by drying shrinkage on the surface of concrete bridges during the long term operation, based on the moisture diffusion theory, an analysis method of the humidity deform coupling was adopted to investigate the concrete bridges＇ long term drying shrinkage deformations and self-induced stress distribution laws and its variations with time under the cyclic humidity conditions. The reliability of the proposed method was verified through comparing the analytical results to the classical experimental results. Though the sensitivity analysis of model size, the rules of drying shrinkage stress distribution along the depth of structure and the various stresses with time under the cyclic humidity conditions were further concluded. The results show that the environmental hmnidity has a significant influence on concrete shrinkage deformation. The trends of concrete specimens＇shrinkage deformation depend on the fluctuation of environmental humidity, especially after 100 days of concrete age. The swelling deformation occurs with the increase of the environmental humidity, and the shrinkage deformation is produced with the decrease of the environmental humidity. The cyclic variation of environmental humidity has little influence on the deformation and the stress condition of the whole structure, accounting for 12% of the total shrinkage deflection. Since the local drying shrinkage stress varies with the cycle of environmental humidity, especially under drying conditions on which the compressed stress increases to --2.7 MPa inside the web. At the same time, the vertical prestress force efficiency is weakened on the concrete surface and the tensile stress of 1 MPa occurs, which increases the risk of web cracking. The analytical results are in good agreement with the states of actual bridge web cracking which is mostly superficial cracks. Due to smaller waving of the environmental humidity inside the box, the changing range of the self-induced stress inside the box girder is smaller than that outside the box girder, which explains the mechanism of a phenomenon that the quantity of surface cracks outside the sections is much more than that inside the sections.
出处
《中国公路学报》
EI
CAS
CSCD
北大核心
2016年第8期77-84,共8页
China Journal of Highway and Transport
基金
教育部高等学校博士学科点专项科研基金项目(20125522120001)
关键词
桥梁工程
循环湿度
湿度扩散理论
干缩自应力
湿度场
开裂风险
bridge engineering
cyclic humidity
moisture diffusion theory
drying shrinkage self-induced stress
humidity field
cracking risk
