基于刚度的大应变FRP约束混凝土模型及其在桥梁抗震加固中的应用

大应变纤维增强复合材料(LRS FRP)由于断裂应变大的特点(>5%),可能在桥墩结构抗震加固中带来较好的延性,近年来成为国内外研究的热点。大应变FRP约束混凝土应力-应变关系设计模型是加固桥墩抗震分析的基础。通过LRS FRP约束混凝土的单调轴压试验,研究了FRP约束刚度参数对应力-应变关系的影响。与基于强度的设计模型由FRP断裂应变确定FRP约束混凝土应力应变关系曲线第2段的斜率(即轴向刚度)不同,轴向刚度由FRP的约束刚度参数决定,由此建立了单调轴压下LRS FRP约束混凝土基于刚度的设计模型。对LRS FRP约束混凝土往复轴压参数(例如卸载曲线、再加载曲线和塑性应变)进行了分析研究,发现塑性应变和应力损伤是影响LRS FRP约束混凝土往复轴压性能的2个关键参数。通过重新定义这2个关键参数,将现有往复轴压荷载作用下传统FRP约束混凝土应力-应变模型推广到LRS FRP约束混凝土。最后,将该模型通过二次开发的方法添加到OpenSees软件平台,对FRP加固桥墩柱的拟静力试验进行数值模拟,模拟结果与试验结果吻合良好,验证了基于刚度模型在桥梁抗震加固分析中的有效性。

Stiffness-based Design-oriented Model for Large-rupture-strain FRP-confined Concrete and Its Application in Seismic Analysis of Bridge Retrofitting

Recently, large-rupture-strain fiber-reinforced polymers (LRS FRPs) has attracted great interest from the research community owing to its LRS characteristic, which may lead to relatively higher ductility in the seismic strengthening of reinforced concrete (RC) bridge piers than those retrofitted by conventional FRP composites. The stress-strain model of LRS FRP-confined concrete is the basis for the seismic analysis of FRP-strengthened RC piers. Based on the monotonic axial compression test of LRS FRP-confined concrete, the influence of confinement rigidity on the stress-strain relationship was studied. Unlike the strength-based design model, which determines the slope of the second section of the stress-strain curve (that is,. the axial stiffness) by the FRP rupture strain, the axial stiffness in this study is determined by the FRP confinement rigidity; thus, a stiffness-based design model of LRS FRP-confined concrete under uniaxial compression is established. The parameters of LRS FRP-confined concrete under cyclic axial compression, such as unloading curve, reloading curve, and plastic strain, were analyzed. Plastic strain and stress degradation were found to influence the cyclic behavior of LRS FRP-confined concrete significantly. By redefining these two key parameters, an existing cyclic stress-strain model was extended to LRS FRP-concrete with good performance. Finally, the model was embedded in OpenSees software to simulate the quasi-static test of piers strengthened by FRP. The simulation results are in good agreement with the test results, thereby confirming the effectiveness of the stiffness-based model in the analysis of bridge seismic reinforcement.