FRP筋增强ECC受弯构件疲劳损伤机理及寿命预测模型研究

In the hrash environment, the structure prone to premature failure caused by fatigue loading which makes the service life shortly. In this proposal, the ECC and FRP bar are used as a composite member to improve durability and fatigue life of the components in engineering. In this project, the fatigue performances of the FRP reinforced ECC beams will be studied through experimental investigations, theoretical analysis and numerical simulations. Firstly, component tailoring of ECC material by means of micromechanical model will be conducted for designing ECC materials, where the domestic PVA fiber is used. Based on the uniaxial tensile and compressive fatigue tests, the fatigue damage constitutive equation of ECC material will be proposed. Then, the bond behavior between ECC and FRP bars will be experimental investigated under fatigue loading. Based the test results, the fatigue damage mechanism of the interface between the FRP bar and ECC will be studied, and a bond-slip constitutive model between ECC and FRP bar will be proposed. Then, a number of FRP reinforced ECC beam will be tested under fatigue loading to study the influence of reinforcement ratio, stress ratio and maximum stress level on fatigue performance. And then, the fatigue response of FRP reinforced ECC beam will be investigated by FEM, and the damage mechanism of FRP reinforced ECC beam will be revealed. Finally, the fatigue life prediction model of FRP reinforced ECC beam will be proposed, which will provide a reference for the fatigue design of FRP reinforced ECC beam.

处于恶劣环境中的工程结构在疲劳荷载作用下易发生过早失效，服役寿命较短。据此，本课题提出采用高延性ECC材料和纤维增强复合筋材（FRP筋）形成复合结构提升结构耐久性和疲劳寿命。本项目拟通过试验研究、理论分析和数值模拟技术，对FRP增强ECC受弯构件的疲劳性能进行深入研究。首先，基于微细观力学设计理论进行国产PVA-ECC配合比优化设计；进行ECC材料单轴拉、压疲劳试验，提出疲劳损伤本构方程。其次，进行FRP筋与ECC的疲劳粘结性能研究，探索疲劳粘结损伤机理，建立粘结滑移本构方程。然后，对FRP筋增强ECC受弯构件进行疲劳试验，研究配筋率、应力比、最大应力水平对其疲劳性能的影响；在此基础上，建立有限元模型对FRP筋增强ECC受弯构件的疲劳力学响应进行数值模拟，揭示其疲劳劣化机理。最后，通过理论分析，确立FRP筋增强ECC受弯构件的疲劳寿命预测模型，为FRP筋增强ECC受弯构件疲劳设计提供参考。

处于恶劣环境中的工程结构在疲劳荷载作用下易发生过早失效，服役寿命较短。采用高延性ECC材料和FRP筋形成的复合结构在提升结构耐久性和疲劳寿命方面有一定的前景。本项目对FRP增强ECC受弯构件的疲劳性能进行研究，具体内容如下：.(1) 采用狗骨试件和圆柱试件对优化设计的国产PVA-ECC材料进行单轴拉、压疲劳试验，研究应力水平对其疲劳性能的影响。结果表明：疲劳拉伸荷载作用下，ECC也表现出多裂缝开裂状态，但裂缝数量相较于静力荷载下少，而且内部纤维多被拉断；疲劳压缩荷载作用下，ECC表现出更高的延性行为。基于试验结果获得了S-N曲线，对其疲劳寿命进行预测，并以残余应变为损伤变量，建立了ECC材料单轴拉、压疲劳本构模型。.(2) 采用中心拉拔进行FRP筋与ECC的疲劳粘结试验，锚固长度为5d，主要考虑应力水平的影响。试验结果表明：在疲劳荷载作用下，试件的破坏模式均为筋材的拔出破坏；随着应力水平的提高，疲劳寿命降低；疲劳荷载作用下，滑移量的发展表现出三阶段倒“S”型特征。基于试验结果，以自由端峰值荷载滑移量为损伤变量，通过数据拟合获得粘结疲劳损伤演化方程，建立了ECC材料与FRP筋粘结滑移疲劳本构模型。.(3) 对21根FRP筋-ECC受弯构件进行静力和常幅疲劳试验，研究配筋率（超筋配置）、筋材类型（CFRP筋和GFRP筋）和应力水平对其疲劳性能的影响。结果表明：静力荷载作用下FRP筋-ECC梁和FRP筋混凝土表现为受压区ECC破坏，疲劳荷载作用下FRP筋-ECC梁和FRP筋-混凝土梁的破坏模式均为筋材的断裂；应力水平较高时，梁的疲劳寿命随着配筋率的增加而增大；随着应力水平提高，FRP筋-ECC梁的疲劳寿命变短，且相同配筋率时GFRP筋-ECC梁的疲劳寿命低于CFRP，且GFRP筋的滑移量大于CFRP筋。.(4) 基于有效惯性矩理论，定义梁的短期刚度，并根据试验数据进行拟合分析，建立了梁刚度退化模型。结合上述建立的材料疲劳本构模型和粘结滑移本构模型，采用MATALB编程，对FRP筋-ECC梁疲劳全过程进行分析。最后，以剩余刚度为损伤变量，建立了FRP筋增强ECC受弯构件的疲劳寿命预测模型。