温差作用下外贴FRP加固混凝土桥梁界面黏结性能研究

Study on Interface Bond Behavior of Concrete Bridge Strengthened with EB-FRP under Temperature Difference

对于暴露在强日照或温差较大环境下的纤维增强聚合物(FRP)加固混凝土桥梁结构,黏结界面中会因温差作用产生一定的温度剪切应力,将减弱界面的后续承载能力。为研究温差作用对FRP加固混凝土界面黏结性能的影响,考虑界面滑移,解析推导了温差作用下弹性-软化-脱黏全过程的界面滑移、黏结应力及FRP应力应变的计算公式,结合试验结果和数值模拟验证了解析式的正确性。分析了环境温差和黏结层数对界面黏结性能的影响,揭示了温差作用下界面黏结剪应力以及FRP正应力的变化规律。解析分析结果表明,温度应力会对界面黏结性能产生不利的影响,实例中界面黏结剪应力最大值能够达到FRP加固混凝土界面剪切强度的51%;粘贴FRP用胶粘剂的玻璃化温度T_g是影响界面黏结性能的关键,当温度未进入胶粘剂玻璃化温度转变区前,界面黏结剪应力呈非线性弹性增长阶段,增加黏结层数可提高界面黏结剪应力;在温度进入胶粘剂玻璃化温度转变区域后,界面滑移呈接近线性分布,界面黏结剪应力分布出现下降段,同时界面黏结强度大幅降低。因此,在实际桥梁工程加固中,须充分考虑环境温差变化对加固结构黏结性能的影响,不可盲目增加FRP黏结层数,且应尽可能采取玻璃化转变温度较高的胶粘剂材料。

For fiber reinforced polymer(FRP) strengthened concrete bridges under strong sunshine or large temperature change environment, thermal stress will appear on the bonding interface due to the effect of temperature difference, which will reduce the interface load capacity. In order to study the influence of temperature difference on the bonding behavior of interface between FRP and concrete, considering the interface slip, the formulas of interfacial slip, bond stress, FRP stress and FRP strain during the whole elastic-soften-debonding process under temperature difference are derived, and the correctness of the analytical formulas are verified by test data and numerical simulation. The influence of ambient temperature difference and FRP layers on the interfacial bonding properties is analyzed, and the change rules of interfacial bonding shear stress and FRP normal stress under temperature difference are revealed. The analytical analysis result show that(1) There is a negative impact on interfacial bonding performance due to the thermal stress, the maximum interfacial bond shear stress achieves up to 51% of the shear strength of the interface between FRP and concrete in the example.(2) The glass transition temperature of adhesive for bonding FRP T_g is the key factor affecting the interfacial bonding properties. When the temperature does not enter the glass transition zone of the adhesive, the interfacial bonding shear stress presents a non-linear elastic growth stage, the interfacial bonding shear stress can be improved by increasing the bonding layers.(3)When the temperature enters the glass transition zone of the adhesive, the distribution of interfacial slip is close to linear distribution, the distribution of interfacial bonding shear stress appears descending stage, and the interfacial bond strength decreases greatly. Therefore, the influence of ambient temperature difference on the bond performance of the strengthened structure must be considered in the strengthening design of bridge engineering, and suitable FRP layers and the adhesive with higher T_g should be used as far as possible.