高应力重复加卸载下GFRP筋与混凝土的粘结性能

Bond behavior between GFRP rod and concrete subjected to high stress reversals

对20个GFRP筋标准拔出试件进行了单调静力加载和高应力重复加卸载的粘结性能试验，考察了粘结强度、加载端滑移量、粘结刚度及滞回耗能的变化规律。研究结果表明，GFRP筋的粘结性能在等幅（△r=0．7τu）应力循环下表现不稳定，在变应力幅重复加卸载下，粘结强度衰减较为明显，得到的包迹线和共同点曲线与单调静力加载r—s曲线形状基本一致，同一滑移量下共同点曲线上的粘结应力与包迹线上的粘结应力比值在0．50～0．75变化。重复加卸载下GFRP筋肋的损伤程度比单调静力加载下的情况更为严重，混凝土界面没有发现劈裂裂纹。从滑移量、能量耗散和刚度衰减变化情况来看，加载历史和损伤累积状态对这些变量的影响最为明显。

Twenty standard bond specimens of GFRP rod were tested under monotonic load and cyclic load to study the changes of bond strength, the slip at the loaded end, unloading stiffness and hysteretic energy dissipation. The results indicate that the GFRP rod does not exhibit steady bond behavior under constant stress reversals （△r=0.7τu ）, and the bond strength of the specimens subjected to variable stress reversals degrades significantly as cycles increase. The envelop curves and the common-point curves show basically the same profile as those r-s curves from the monotonic static test. The ratios of the bond stresses in the common-point curves to those in the envelop curves at the same slip range from 0.50 to 0.75. More serious damage can be observed around the ribs of the GFRP rod in the specimens after stress reversals than those subjected to monotonic static test. No splitting cracks can be seen in the concrete. From the investigation of the slip at the loaded end, hysteretic energy dissipation and unloading stiffness as reversals increase, the load history and accumulative damage status were found to be the two key influencing factors.