预应力碳纤维板加固钢筋混凝土梁疲劳主裂纹扩展试验研究

Experimental Study on Propagation Behavior of Main Fatigue Crack in RC Beam Strengthened with Prestressed CFRP Plate

运用理论分析和试验,研究预应力碳纤维板（CFRP）加固的钢筋混凝土（RC）梁在疲劳荷载作用下主裂纹的扩展规律。基于I型裂纹尖端的力学分析模型,推导加固梁的应力强度因子计算式,结合裂纹扩展的试验数据,拟合得到加固梁疲劳裂纹在稳定扩展阶段的扩展速率Paris半经验表达式。结果表明：加固梁的疲劳主裂纹扩展可分为快速发展、稳定扩展和失稳扩展3个阶段,其中稳定扩展阶段占加固梁疲劳寿命的92%-96%左右;适当提高预应力水平对加固梁的疲劳寿命有利;在相同试验条件下,预应力水平为20%的加固梁与预应力水平为30%的加固梁相比,其疲劳裂纹的扩展速率大1.28%-3.84%;给出的主裂纹疲劳扩展速率半经验公式可方便、较准确地预测该类加固构件的疲劳寿命,相对误差为11.72%-20.33%。

The propagation rules of main crack in reinforced concrete（RC）beam strengthened with prestressed carbon fiber reinforced polymer（CFRP）plate were investigated by theoretical analysis and experiments.The mechanical analysis model of mode I crack tip was built to derive the formula for the stress intensity factor of strengthened beam.The semi-empirical expression,in a similar form to the Paris formula,of the growth rate of fatigue crack in strengthened beam during stable propagation stage was obtained by fitting the experimental data of crack propagation.Results show that the propagation of the main fatigue crack in strengthened beam can be divided into three stages,namely,rapid development,stable propagation and unstable propagation.Among which,the stable propagation stage lasts for about92% ~96% of the fatigue life of strengthened beam.The appropriately higher level of prestress is favorable to the fatigue life of strengthened beam.Under the same test conditions,the growth rate of fatigue crack in strengthened beam with 20% of prestress level is 1.28%~3.84% greater than that with30% of prestress level.The proposed semi-empirical formula for the fatigue growth rate of main crack can conveniently and more accurately predict the fatigue life of such strengthened members,and the relative error is 11.72%~20.33%.