碳纤维布约束型钢混凝土矩形短柱轴心受压性能研究

According to current research on structural rehabilitation, this project intends to study on axial compressive mechanical performance of steel reinforced concrete rectangular short columns confined by carbon fiber reinorced plastics sheet. By variation of service loading, corner radius and strengthening ratio, axially monotonic static compression tests of strengthened components are finished to explore confinement mechanism and failure modes. Then nonlinear finite element method is used to simulate experimental specimens, more parameters analyses are done after the verification of accurate models, the discipline of concrete stress distributio on column section and the recognition of CFRP sheets hoop orientation working strain are presented, the change of failure modes is also explored. Based on former results, considering the service loading and corner radius, a new constitutive model of steel reinforced concrete confined by CFRP sheets is set up; the boundray between lightly and heavily confined corresponding confinement ratio is defined and failure modes are distinguished; a design method with formulas of ultimate axial compressive bearing capacity of specimens under service loading are provided. This study is aimed for theoretical proposal of CFRP use on strengthening SRC composite structure.

根据目前结构加固的现状，本课题拟对碳纤维布约束型钢混凝土矩形短柱轴心受压力学性能进行研究。变化加固组合柱中的负载水平、倒角半径和加固率参数，通过单调静力加载试验，研究其破坏模式和受力机理。之后对加载破坏过程进行非线性有限元模拟和参数分析，探寻负载水平和倒角半径变化下，矩形柱截面中受约束混凝土应力分布和碳纤维布的应变发挥规律，以及构件破坏模式的改变。最后在试验和数值计算基础上进行理论分析，建立考虑负载和倒角半径条件的约束混凝土本构模型，针对负载下的碳纤维布加固型钢混凝土矩形短柱，定义强弱约束加固界限和对应加固率，区分破坏模式，并提出相应设计方法和构造措施。以期为纤维增强复合材料加固钢和混凝土组合结构理论做出贡献。

本课题对碳纤维布约束型钢混凝土矩形短柱轴心受压力学性能进行了研究。选取加固柱中的负载水平、倒角半径、加固率和条带式等参数，分两批共浇筑了32个构件，通过单调静力加载试验，全面认识了约束柱的破坏过程和机理。.通过试验发现，碳纤维布约束能明显提高了柱的承载力，改善了柱屈服后变形能力，但约束型钢柱总体承载力提高幅度低于约束钢筋混凝土柱。试验中约束柱破坏形式均是纵筋和型钢先屈服，随后核心混凝土被压碎，最终碳纤维布断裂，破坏前有明显的预兆。随着预载水平的提高，碳纤维布有效拉应变系数逐渐降低，约束柱的屈服荷载、峰值荷载和延性总体呈降低趋势。随碳纤维布层数增大而提高，约束柱的峰值荷载在包裹2层CFRP布下提高了58. 36%，3层下提高了64. 51%；预载会减弱CFRP布对短柱的约束效果，随着预载水平的提高，碳纤维布有效拉应变不断减小，柱的承载能力不断降低。随着倒角半径的增大，倒角处应力集中现象得到减缓，碳纤维布的有效拉应变增大，内部混凝土的受到的约束作用越大，构件在整体横截面积减小的情况下承载力依然升高，且随着倒角半径的增大构件破坏模式有由弱约束向强约束转化，荷载位移曲线中的下降段逐渐消失。.以试验数据为基础，根据碳纤维布约束有预载型钢混凝土矩形短柱的受力特点，使用ABAQUS软件建立了有限元模型，采用阶段分析和单元生死技术，对柱预载、加固和加载这一试验过程进行模拟，通过定义混凝土损伤塑性(Concrete Damaged Plasticity，简称CDP)模型中的损伤因子来考虑预载对混凝土材料性能的影响，计算结果与试验结果吻合较好。通过数值分析发现，碳纤维布对矩形截面型钢混凝土柱的约束作用主要集中在水平截面的柱角部和靠近型钢的核心位置，当加载到80%的峰值荷载时才有明显的约束作用；随着预载水平的增大峰值荷载时混凝土竖向应力不断降低，且柱角部混凝土应力的变化最明显。峰值荷载时，碳纤维布在柱中部的环向相对应变约为柱角部相对应变的2倍，且各位置上碳纤维布应变值随预载水平的增大而降低。