基于高轴压徐变和氯盐侵蚀的纤维超高强RC柱在高强箍筋约束下的力学性能研究

Ultra high strength materials are gradually utilized in engineering construction due to the requirements of the ultrahigh strengthen and long service life for civil engineering raised by the economic development and social progress. In this project, the research work can be divided into four parts based on experimental investigation and theoretical analysis, as follows: 1) to evaluate restrain effect of the high- strength stirrup and ductile property of the compressed softening curve based on short-term compressive test of restrained stirrup ultra-high strength RC column with multi variable factors; and combined with actual stress of the restrained stirrup, to propose the axial compressive constitutive model; 2) to establish the modified creep coefficient based compressive computation method, based on calculation of creep of ultra-high RC beam with long-term high stress; 3) to study the autogenous shrinkage of restrained ultra-high strength concrete, the microscopic interface and macroscopic damage characteristics, combined with analysis of heat conduction, and to establish the quantitative stress equation of autogenous shrinkage; 4) to examine the reduction law of mechanical loads due to environmental factors, and to propose the modified long-term creep calculation method under chloride erosion condition. The short- and long-term stress-strain mechanical models of ultra-high strength RC beam with concrete compressive strength of 150MPa and stirrup strength of 1000MPa will then be established based on above research findings. The safety design will also be promoted under seismic effect.

本课题，依据经济发展与社会进步对土木工程提出的超高强化及长使用寿命的要求，面向超高强材料逐步应用于工程结构这一大的建设背景，基于试验研究及理论分析从以下四个方面展开项目研究：1）通过对箍筋约束超高强RC柱在多因素变动下的短期轴压试验，评价高强箍筋约束效果及压缩软化曲线的韧性性能，结合约束箍筋的实际应力水平，提出轴压本构模型；2）通过长期高轴力作用下的超高强RC柱徐变计算分析，形成基于修正徐变系数的压缩特性计算方法；3）研究约束条件下超高强混凝土自收缩发展机制，考虑材料微观界面性能及构件宏观损伤特征，结合热传导分析建立自收缩应力定量表达式；4）检讨环境因素对力学荷载的衰减规律，提出氯盐腐蚀下长期徐变计算的修正计算公式。结合上述四部分研究成果，建立混凝土抗压强度150MPa级及箍筋强度1000MPa级的超高强RC柱的短、长期应力-应变力学模型，为地震作用下的安全性设计奠定基础。

本课题通过对PVA纤维超高强混凝土柱轴压性能的研究，建立PVA超高强混凝土结构构件的力学性能分析模型，形成超高强混凝土的设计方法；通过对足尺寸超高强混凝土柱自收缩机理的研究，提出超高强混凝土柱在约束条件下的自收缩发展机制；并提出长期作用下应力—应变衰减的模型，应用于滨海超高强混凝土柱实际设计中，以保障超高强混凝土柱的安全性与耐久性。.研究主要内容：（1）根据工程中常见的未待混凝土成熟硬化即开始加载施工的实际情况，基于混凝土龄期和PVA纤维体积掺量来研究早龄期加载的超高强混凝土长短期荷载作用下的力学与徐变性能。（2）通过对66根超高强混凝土柱的试验，研究了箍筋间距，箍筋直径，箍筋强度，箍筋带肋，箍筋约束形式，截面形式，截面尺寸，构件高度，混凝土强度，纤维体积掺量对超高强混凝土构件本构曲线，承载力和延性的影响。（3）借助有限元模拟软件对混凝土柱在单调轴压加载情况下进行非线性模拟分析，通过软件得到钢筋的应力状态、混凝土柱轴向受压承载力、荷载位移曲线与试验曲线进行比较，得出较为吻合的实验结果与规律。（4）收集既有约束混凝土柱实验数据对人工神经网络进行训练，获得输入参数包含对于约束混凝土柱峰值应力有影响的变量的人工神经网络，并对各单变量进行分析。