约束混凝土徐变机制及其对圆钢管约束混凝土柱静动力性能影响

Steel tube confined RC columns (SCRC) have a promising future in high-rise structures, due to their ease in connection, high compressive strength and excellent seismic behavior. The high energy dissipation capacity of SCRC can relax the strict limitation on their load ratio in the service design and solve the dilemma between the extremely low shear-span ratio of the columns and the high requirements in the seismic performance of the structures. To date, no investigation is available for the long-term behavior of such innovative composite members, despite of the importance in providing reliable prediction of their creep deformation for both seismic design and service design of the high-rise structures. The available creep model and analysis method cannot be implemented to SCRCs directly due to the significant difference between their mechanical behavior and those of concrete-filled steel tubular columns or RC columns. In this context, this project will conduct experimental and numerical investigation to reveal the linear and non-linear creep behavior of confined concrete under different level of sustained loading and their influence on the static and seismic performance of SCRC. Linear and non-linear creep models and the corresponding analysis method are provided for confined concrete accounting for the time-dependent confinement effects and the difference of the cross-sectional stress redistribution along the column length. Designing methods are proposed to predict the seismic resistance of SCRCs taking account of the concrete damage induced by non-linear creep and time effects on the capability for the steel tube in providing confinement effects. The outcome of this research project will improve the designing theory of SCRC and also provide references for the research on the long-term behavior of steel tube confined SRC columns and FRP confined concrete columns.

圆钢管约束钢筋混凝土抗压承载力高、抗震性能好、节点构造简单，用于（超）高层结构，可有效解决结构柱低剪跨比、高轴压比与结构抗震性能需求之间的矛盾，应用前景广阔。但是，目前关于圆钢管约束钢筋混凝土柱长期性能研究尚属空白。鉴于该类组合构件与钢筋混凝土、钢管混凝土构件徐变机理的显著差异，不能套用现有徐变模型与分析方法进行长期性能预测，而准确预测竖向构件徐变变形、科学评估徐变对其滞回性能的影响，对保证结构安全至关重要。为此，本项目以圆钢管约束钢筋混凝土柱为研究对象，重点揭示被动约束混凝土线性与非线性徐变机制；建立可考虑约束作用经时效应的线性与非线性徐变模型与分析方法；提出可考虑截面应力沿柱高不均匀分布的长期压缩变形预测方法；考虑徐变对钢管约束作用影响及对混凝土造成的损伤，建立抗震性能设计方法。研究成果将进一步完善圆钢管约束钢筋混凝土柱设计理论，也可为FRP约束混凝土的徐变性能研究提供参考。

圆钢管约束钢筋混凝土柱抗压承载力高、抗震性能好、节点构造简单，在（超）高层结构中有较为广阔的应用前景。但现有研究仅针对短期性能与抗震性能开展，关于长期性能的研究尚属空白。而准确预测竖向构件徐变变形、科学评估徐变对其滞回性能的影响，对保证结构安全至关重要。为此，本项目以圆钢管约束钢筋混凝土柱为研究对象，完成以下工作：.（1）进行了17组短柱线性徐变试验（持荷440天）、7组短柱非线性徐变（持荷140天）以及3组中长柱长期持荷试验（持荷140天）。重点关注了外包钢管对钢管约束混凝土长期静力响应的贡献，揭示了被动约束混凝土线性与非线性徐变机制，分析了钢管纵向受力及约束效应沿柱长方向不均匀分布现象；确定了影响钢管约束混凝土柱长期性能的关键参数；对比分析了钢管约束混凝土与同用钢量钢管混凝土长期性能的差异。 .（2）在试验研究的基础上，建立了可考虑约束作用经时效应的线性与非线性徐变模型与分析方法，提出了可考虑截面应力沿柱高不均匀分布的长期压缩变形预测方法,具有良好预测精度，线性回归系数和判定系数分别为0.978和0.948。在此基础上，进行广泛的参数分析，并提出适用工程设计的简化计算方法。.（3）在长期持荷试验结束后，进行了压溃试验，研究了长期持荷作用对试件刚度、轴压承载力、峰值应变的影响，并分析了其对约束效应及钢管纵向受力的影响。结果表明，长期持荷在略微提高轴压承载力的同时，会减小峰值应变，减小幅度达4.8%~20.0%，且该影响对早龄期加载试件更为显著。.（4）考虑徐变对钢管约束作用影响及对混凝土造成的损伤，建立了长期持荷后抗震性能分析计算有限元模型，并在此基础上分析了长期持荷对构件抗震性能的影响。研究结果表明，长期持荷对构件抗震性能的影响有限，初始刚度及水平承载力影响幅度最大仅6.6%和4.3%。.研究成果将进一步完善圆钢管约束钢筋混凝土柱设计理论，也可为FRP约束混凝土的徐变性能研究提供参考。